How do i calculate due date

Calculate your due date: How to find your baby's due date

Choose a calculation method Last periodConception dateI know my due date

First day of my last period

BabyCenter's Due Date Calculator

Use our pregnancy due date calculator by plugging in either the date of your last menstrual cycle or the date you know you conceived. The calculator will do the rest.

How is my due date calculated?

There are several ways your due date is determined. If you happen to know the day you conceived, you can count 38 weeks from that day to find your due date. (Human gestation takes about 38 weeks.)

But very few expectant moms know exactly when they conceived. Even if you only had sex once during your fertile period, you wouldn't conceive on that day unless you happen to be ovulating. Sperm can live for up to five days inside your fallopian tubes. So, it could be up to five days after you have sex that you release an egg (ovulate) and it gets fertilized by a waiting sperm. That's the day you conceive.

So, without knowing the day of conception, how does anyone determine a due date?

First day of your last period

The most common way to calculate your pregnancy due date is by counting 40 weeks from the first day of your last menstrual period (LMP). And that's how most healthcare providers do it.

If your menstrual cycle length is the average length (28-day cycle), your menstrual cycle probably started about two weeks before you conceived. This explains why pregnancies are said to last 40 weeks instead of 38 weeks.

This method doesn't take into account how long your menstrual cycle actually is or when you think you might have conceived. But generally speaking, women typically ovulate about two weeks after their menstrual cycle starts. And women are more likely to know when their last period started than the day they ovulated.

Conception date

If you do happen to know precisely when you conceived – say, if you were using an ovulation predictor kit or tracking your ovulation symptoms – you can calculate your pregnancy due date based on your conception date. Just choose that calculation method from the pulldown above and put in your date.

Note: Again, you don't necessarily conceive on the day you have sex.

IVF transfer date

If you conceived through IVF, you can calculate your due date using your IVF transfer date. If you had a Day 5 embryo transfer, count 261 days from your transfer date. If you had a Day 3 embryo transfer, count 263 days.

Can my due date change?

Your healthcare provider might revise your due date if your baby is measured during a first trimester ultrasound scan and found to be much bigger or smaller than expected for gestational age. This is more likely to happen if you have an irregular menstrual cycle length that makes it hard to pinpoint the date of conception.

Your healthcare provider will measure your baby during that ultrasound exam to figure out how far along your baby is and then provide you with a new due date.

What if I already know my due date?

If you already know your due date, you can use this calculator to see your pregnancy timeline. It will tell you when you'll hit various milestones, and when you may be due for prenatal tests and prenatal visits. You'll also find what your baby's sign and birthstone will probably be and which famous people were born on your due date.

How likely am I to give birth on my due date?

Of course, a due date calculation is always approximate, whether it's from our tool or from your doctor or midwife. Only 1 in 20 women delivers on their due date. You're just as likely to go into labor any day during the two weeks before or after.

Want more information about how the weeks, months, and trimesters of pregnancy are counted? See our pregnancy timing chart.

How soon can I take a pregnancy test?

With all this talk about pregnancy due dates, you may be wondering when you can take a pregnancy test. To ensure you get the most accurate reading, it's best to wait a few days after your missed period to take a pregnancy test.

At-home urine tests measure the amount of hCG (human Chorionic Gonadotropin) present in your body. If you take a pregnancy test before you miss your period, you may not get an accurate result, despite what some tests advertise.

If you're getting a blood test in your provider's office, you may get results sooner. These tests also measure the amount of hCG in your bloodstream, but they're more sensitive than at-home urine tests. Blood tests may be able to detect pregnancy six to eight days after ovulation.

Read more

Your pregnancy, week by week
Your first trimester pregnancy checklist
Pregnancy Weight Gain Calculator
Ovulation Calculator
See all tools

How many weeks pregnant am I? — Flo

The first day of your last period The day you conceived

Average cycle length

20 days21 days22 days23 days24 days25 days26 days27 days28 days29 days30 days31 days32 days33 days34 days35 days36 days37 days38 days39 days40 days41 days42 days43 days44 days45 days

Please note that Flo Health does not collect, process, or store any of the data that you enter while using these Tools. All calculations are done exclusively in your browser. Flo Health does not have access to the results. All data will be permanently erased after leaving or closing the page.
Our Due Date Calculator is based on a 28-day cycle (cycles can vary from 20 to 45 days), and your period and ovulation are considered to be the first 2 weeks of pregnancy. As this method is affected by the regularity of your menstrual cycle, the due date predictor is not 100% accurate.
Remember that pregnancy due date calculators, birth date calculators, and pregnancy calculators can help you learn more about your estimated due date and pregnancy timeline, but they are not a replacement for medical advice. You should always notify your health care provider that you are pregnant. Sometimes an ultrasound will be needed to date your pregnancy.

You will meet your baby on

date

day

Gestational age is

weeks and day

Gestational age is the age of pregnancy and is counted from the first day of your LMP. So technically it includes two weeks during which you weren't pregnant yet.

Week 1

At 1 week pregnant, you’re actually not pregnant yet. As your pregnancy is calculated from the first day of your last menstruation, your baby does not yet exist, and your body is preparing for the ovulation during which you’ll get pregnant.

Week 2

At 2 weeks pregnant, you’re technically not pregnant yet. Right now there is a lone egg and a whole bunch of anxious sperm eager to fertilize the egg. Your uterus and the entire body are preparing for a big day of ovulation - the stage when you'll get pregnant.

Week 3

Week 3 of pregnancy is the week when the implantation happens. Your body releases chorionic gonadotropin (hCG), which causes an increased production of estrogen and progesterone, and prevents new eggs in the ovaries from ripening. Very soon you'll start experiencing the first symptoms of pregnancy: missed period, nausea, breast changes.

Week 4

At 4 weeks pregnant, your baby is the size of a poppy seed.

At 4 weeks pregnant, your future baby has finally found his home for the next eight months. The blastocyst has arrived from a fallopian tube to your uterus. You can get a positive pregnancy test result at this stage.

Week 5

At 5 weeks pregnant, your baby is the size of a sesame seed.

By week 5, you should have missed your period, which is one of the most obvious sign you're expecting. Under the influence of hormonal changes, you can feel the first signs of pregnancy: breast swelling, fatigue, headache, and back pain.

Week 6

At 6 weeks pregnant, your baby is the size of a lentil.

Starting from pregnancy week 6, you may experience morning sickness. This is the result of hormonal changes occurring in your body. Malaise, breast swelling, darkening of the nipple areola, and frequent urination can bother you, too. In case of bleeding, you should consult your doctor.

Week 7

At 7 weeks pregnant, your baby is the size of a blueberry.

At 7 weeks pregnant, symptoms start kicking in and your uterus almost doubles in size. Be prepared for a possible increase in nausea, fatigue, heartburn, and other pregnancy symptoms. Morning sickness may give a lot of trouble. Try to find some ways to cope with it.

Week 8

At 8 weeks pregnant, your baby is the size of a bean.

At 8 weeks pregnant, you need to plan your first visit to the gynecologist. The doctor will prescribe the necessary tests and examinations for the first trimester of pregnancy. You may feel the growing discomfort of morning sickness. Try to be patient; it usually lasts until the 14th week only.

Week 9

At 9 weeks pregnant, your baby is the size of a cherry.

At 9 weeks pregnant, your baby is already about 0.6–0.7 in (16–18 mm) and weighs about 0.11 oz (3 g). The tail has disappeared; human features are becoming more distinct. The joints of his/her hands and legs can flex; the nipples and hair follicles are developing. Taste buds are beginning to form on the tongue, as well as primary tooth buds in the gums.

Week 10

At 10 weeks pregnant, your baby is the size of a kumquat.

Week 10 of pregnancy is the time when almost all vital organs and tissues of your baby have formed. Now, they are beginning to function and grow rapidly. He or she can swallow amniotic fluid and move their arms and legs. The skin is getting covered with small hair and the fingers have tiny nails. Testes in boys already start to produce testosterone.

Week 11

At 11 weeks pregnant, your baby is the size of a fig.

At 11 weeks pregnant, your baby has already reached 2 in (5 cm) in size. Now, his/her head is half the length of the body, but in the coming weeks, the body will grow enough to make up for it. The fetus skin is so thin and translucent that through it you can see an extensive network of vessels. Placental vessels are expanding to provide the fetus with necessary nutrients and oxygen.

Week 12

At 12 weeks pregnant, your baby is the size of a plum.

At 12 weeks pregnant, your baby weighs about 0.49 oz (14 g). His/her vocal cords are forming, and kidneys are starting to produce urine, filling the bladder. Although you cannot feel it yet, you can see the baby during a sonogram screening (ultrasound).

Week 13

At 13 weeks pregnant, your baby is the size of a pea pod.

Welcome to the last week of the first trimester! Most early pregnancy symptoms will soon be left behind. At 13 weeks pregnant, your baby is constantly growing. Now, he/she is more than 2. 8 in (7 cm) from the top of his/her head to the coccyx.

Week 14

At 14 weeks pregnant, your baby is the size of a peach.

At 14 weeks pregnant, your baby is developing rapidly. In a while, you will be able to feel them moving and kicking. Your body starts actively gaining weight. This occurs due to an increase in blood and lymph volume.

Week 15

At 15 weeks pregnant, your baby is the size of an apple.

At 15 weeks pregnant, your baby your baby is actively drawing in amniotic fluid through his/her nose. Very soon you'll start looking pregnant indeed as your uterus has risen from your pelvic region to your lower abdomen. Time to plan pregnancy shopping!

Week 16

At 16 weeks pregnant, your baby is the size of an avocado.

You’re on week 16 of your pregnancy, and things are really starting to gear up! Your tiny baby is not so tiny anymore, and it most definitely looks like a human baby now. By week 16 of your pregnancy, you’re 4 months in. That means you’re nearly halfway there and only have 5 more months to go!

Week 17

At 17 weeks pregnant, your baby is the size of a potato.

If you’ve been enjoying a relatively subtle pregnancy with very little belly to show for it, that’s probably over now! Your waist will gradually disappear as your uterus moves upwards and out of your pelvis.

Week 18

At 18 weeks pregnant, your baby is the size of a bell pepper.

If you’ve been astonished by your baby’s rapid growth and weight gain over the last few weeks, by week 18 this will start to level off a little — but there’s still lots of big news in your little one’s early life! At this stage, he or she can yawn, stretch, and even make facial expressions like frowning. The baby’s sense of taste is developing, and taste buds can now distinguish between sweet and bitter.

Week 19

At 19 weeks pregnant, your baby is the size of a mango.

At 19 weeks pregnant, your rounded belly is very noticeable. The first hair appears on the baby's head, and the brain areas responsible for the senses — tactile, gustatory, olfactory, visual and auditory — are developing rapidly.

Week 20

At 20 weeks pregnant, your baby is the size of a grapefruit.

Congratulations! You are halfway to meeting your baby. The baby's legs have almost straightened, so from now on, he/she will be measured from head to toe.

Week 21

At 21 weeks pregnant, your baby is the size of a banana.

As a 21 week pregnant woman, you have crossed the halfway line on your journey to becoming a mother. Your baby is getting bigger. You can now definitely feel her presence as she explores the real estate that you’ve prepared for her.

Week 22

At 22 weeks pregnant, your baby is the size of a carrot.

If you are entering the 22nd week of your pregnancy, without doubts it is getting crowded in there! Your baby is growing and invading your space. And your uterus stretches to about 2 cm (0.8 in) above your belly button to fit your growing baby.

Week 23

At 23 weeks pregnant, your baby is the size of a squash.

For many women, being 23 weeks pregnant is an exciting time because you may finally be showing your baby bump! Among other things, your baby’s eyes and lips are taking shape. They will begin to gain weight more weight which will eventually fill out their wrinkly skin.

Week 24

At 24 weeks pregnant, your baby is the size of an eggplant.

At 24 weeks pregnant, your baby is almost a foot long. You could be experiencing a tingling sensation in your joints, which is known as carpal tunnel syndrome. It is a common condition during pregnancy which occurs due to fluid build-up in your joints which results in compression of the median nerve.

Week 25

At 25 weeks pregnant, your baby is the size of a full ear of corn.

Once you reach week 25 of your pregnancy, you’ll be nearing the end of your second trimester. It can feel like times flies! At 25 weeks pregnant, you’re approximately 5 months and 2 weeks along. Your baby has been growing steadily and even though it’s still not ready, it won’t be long before it comes into the world.

Week 26

At 26 weeks pregnant, your baby is the size of a beetroot.

You’re likely to put on between 16 and 22 pounds by now. At one point during this week, your baby will open his or her eyes for the first time. He or she is not yet able to see anything inside of the uterus but will blink closing and opening his or her eyes when falling asleep and waking up.

Week 27

At 27 weeks pregnant, your baby is the size of a cauliflower.

The 27th week of the pregnancy marks the final two weeks of the second trimester. If your baby is more active at night you might suffer from insomnia and have trouble sleeping. Compensate for the lack of sleep time during the night by napping during the day more when the baby is sleeping.

Week 28

At 28 weeks pregnant, your baby is the size of a coconut.

At 28 weeks you are now entering the third trimester of your pregnancy. At this stage, your baby is pretty well-developed. Her organs, tissues, and nerves continue to grow, but she already has all of the systems necessary for survival outside the uterus. Towards the end of the pregnancy, babies start to recognize familiar sounds and voices.

Week 29

At 29 weeks pregnant, your baby is the size of a pomelo.

At 29 weeks pregnant, you're likely to develop varicose veins like 40 percent of expectant moms. It's also a good time to start doing a kick count. Let your doctor or midwife know if you notice that your baby is becoming less active.

Week 30

At 30 weeks pregnant, your baby is the size of a head of cabbage.

At 30 weeks pregnant, you are likely to experience shortness of breath. Your baby is still up high near your rib and is waiting a bit – it is soon expected to drop down into your pelvis.

Week 31

At 31 weeks pregnant, your baby is the size of a head of a zucchini.

At 31 weeks pregnant, your breasts can get leaky producing the first baby’s food – colostrum. This is one of the symptoms that your body is getting ready for the big day. You are likely to experience shortness of breath. This week your baby is going through major nerve and brain development.

Week 32

At 32 weeks pregnant, your baby is the size of a head of lettuce.

At 32 weeks pregnant, your body may start flexing its muscles preparing for the big day. Your baby is also preparing for her debut mastering the skills she’ll need to thrive outside your womb: swallowing, breathing, sucking.

Week 33

At 33 weeks pregnant, your baby is the size of a pineapple.

At 33 weeks pregnant, you may notice that your baby’s movements are affected by your daily routine. Your belly continues to grow and it’s getting even more troublesome to find a comfortable sitting or sleeping position.

Week 34

At 34 weeks pregnant, your baby is the size of a butternut squash.

At 34 weeks pregnant, your breasts could start leaking small amounts of yellowish colostrum. Your baby is already the size of a school bag and weighs as a melon. If you’re worried about your safety at work, time to talk to your employer about maternity benefits.

Week 35

At 35 weeks pregnant, your baby is the size of a honeydew melon.

At 35 weeks pregnant, you may know how your baby’s moving in your womb just by looking at your bump. It can you give you some discomfort and make you a bit breathless. At this point, many moms can’t wait for the baby to get here, while others are feeling a bit anxious about giving birth. Both feelings are completely normal!

Week 36

At 36 weeks pregnant, your baby is the size of a papaya.

At 36 weeks pregnant, your baby is sleeping between 60 and 80% of the time. It has finally moved into your pelvic cavity, the pressure on your diaphragm is released, and lightening happens. Your baby can now open its eyes, suck its thumb, breathe, and recognize voices!

Week 37

At 37 weeks pregnant, your baby is the size of a head of romaine lettuce.

Welcome to your 37th week of pregnancy, and congratulations! The baby moves further into the pelvis. It is considered to be ‘at-term’ and can actually arrive any day now. Make sure you are ready for the arrival of a new family member.

Week 38

At 38 weeks pregnant, your baby is the size of Swiss chard.

At 38 weeks pregnant, you can find yourself spending the whole life peeing. The pressure on your bladder is tremendous. Your baby is a fully functioning little human and your placenta is fully grown.

Week 39

At 39 weeks pregnant, your baby is the size of a small watermelon.

Welcome to the week 39 of pregnancy! Your baby is full term, meaning that it is fully developed and is only waiting for the right time to make an entrance into the world. Have you prepared everything that is needed to welcome your baby?

Week 40

At 40 weeks pregnant, your baby is the size of a mini watermelon.

At 40 weeks pregnant, you may feel disappointed that your due date has come and gone. Don’t panic and make the last preparations for a new human who’ll soon join the world.

Week 41

At 41 weeks pregnant, your baby is the size of a pumpkin.

At week 41 of pregnancy, you might be dying out of the desire to give birth and see your baby. But rest assured that plenty of moms-to-be go past their due date and everything turns out just fine.

Week 42

At 42 weeks pregnant, your baby is the size of a watermelon.

When a pregnancy lasts for 42 weeks or more it is referred to as a post-term pregnancy. While not many studies exist that prove why some women’s pregnancy lasts for 42 weeks, medical experts believe that factors such as hormones, genetics, and even obesity can be the cause.

Barbara Levy, MD

Former Vice President in Health Policy of the American College of Obstetricians and Gynecologists National Leadership Institute, CA, USA

If you’ve taken a pregnancy test and it appears to be positive, you might be wondering what happens next. That’s where our due date calculator or due date predictor comes in.

By using some basic information about your last period and cycle length, our pregnancy calculator can help you work out your estimated due date (EDD — aka when you might meet your baby). This information is also useful if you’re thinking about the baby’s due date timings before you start trying to conceive.

Try using our EDD calculator now and then scroll down for more on how due dates (and pregnancy) are calculated, plus information on when you could have conceived and how far along you might be.

Note:

If you’ve already had your first ultrasound scan, you can use our Due Date by Ultrasound Calculator instead.
Or, if you have conceived through in vitro fertilization (IVF), you can use our IVF and FET Due Date Calculator.

How far along am I?

One of the first questions you’ll probably have after discovering that you’re pregnant is “How pregnant am I?” Interestingly, there are two ways to measure the age of a baby during pregnancy — gestational age vs fetal age — but health care providers generally use gestational age only because it’s deemed more accurate.

More on those below, but when you know how far into your pregnancy you are, you can get a clearer idea of your expected date of delivery. This is another name for a due date, meaning your EDD is the approximate date when labor is expected to begin. As we’ll explain if you scroll down, this date is really just an estimate, so you can expect to go into labor anytime in the two weeks before and after your due date.

How far along am I? Gestational age

To track pregnancy and calculate a due date, doctors use gestational age. Gestation is how long a person is pregnant in weeks, and gestational age is measured from the last menstrual period (LMP) — the first day of your last period — to the current date in weeks.

In general, pregnancies last anywhere from 38 to 42 weeks (or around 280 days). If a baby is born before 37 weeks, they are considered premature.

How far along am I? Fetal age

The other method of measurement is fetal age. While gestational age measures how far along a pregnancy is in weeks, fetal age is the actual age of the growing baby. To calculate this, you work out the amount of time from the date of conception (which is around two weeks later than your LMP in a 28-day cycle but varies depending on cycle length) to the current date in weeks. However, this is a far less common measurement for pregnancy because it’s often hard to pinpoint exactly when you ovulated (and therefore the moment of conception).

How is due date calculated?

Lots of us assume that a pregnancy is exactly nine months long, but that’s not the case. To work out how to calculate pregnancy weeks, there’s a little more to it.

“The nine months of a pregnancy are actually 40 weeks,” Dr. Charlsie Celestine, Flo board member, obstetrician, and gynecologist (OB-GYN), explains. “The due date is 40 weeks from the first day of your last menstrual period. But some women can go beyond that to 41 weeks. ”

In fact, the first thing you’ll likely notice when you let your health care provider know you are pregnant is that pregnancy is calculated in weeks rather than months. And your baby’s estimated due date falls on the 40th week, when you’ll actually be around 10 months pregnant.

That’s to account for the fact that pregnancy is measured according to gestational age, not fetal age. So that means you count pregnancy from your LMP, not the date you conceived, adding an extra two weeks even though you weren’t technically pregnant then. Also, this method recognizes that not all months have the same number of days, so you’ll likely still be pregnant at nine months.

You might also see figures like 13/5 or 13+5 in your doctor notes. Pregnancy is counted in complete weeks, so 13/5, 13+5, or a variation of this would mean you’re 13 weeks and 5 days pregnant. Learn more about how you count pregnancy weeks here.

Your health care provider will usually calculate your due date based on one or a combination of the following methods, so let’s find out more about how they work.

How to calculate due date: Naegele’s rule

As we now know, the most commonly used method to calculate due date is to count “40 weeks from the first day of your LMP,” Dr. Celestine says, adding that this is usually done at your first appointment.

This method is also known as Naegele’s rule. “You calculate [EDD] using the first day of the last menstrual period [adding exactly one year to it], add seven days to that, and then subtract three months,” she explains.

It’s worth noting that this rule considers a regular menstrual cycle to be 28 days long, but it’s totally normal for a person’s cycle to vary from anywhere between 21 and 45 days. If your cycle lasts longer, the estimated due date will likely be later. If you have a shorter cycle, your due date may be earlier.

How to calculate due date: Period wheel

“More commonly, I use a pregnancy wheel using the first day of the menses [period],” says Dr. Celestine, explaining how she tends to work out the due date in her patients.

A pregnancy wheel or gestation calculator is a simple calendar that works out your EDD or baby’s birth date based on different inputs, such as your LMP. OB-GYNs can also use a pregnancy wheel as a pregnancy timeline calculator to work out when you’ll have certain scans and screenings, along with your trimester dates.

How to calculate due date: Ultrasound scan

As you’ve seen above, there are numerous ways to calculate an estimated due date — most involving the date your last period started. But an ultrasound scan in the first trimester is used to check that the dating based on the last menstrual period is correct. This is especially important if your period doesn’t always arrive at the same time each month.

“The LMP is compared to an ultrasound because some women have irregular cycles [and some can’t remember when their last period happened], so their LMP is not the most accurate,” Dr. Celestine explains.

“On ultrasound, I would measure the length of the fetus, called the ‘crown–rump length,’ in the first trimester to get the gestational age or due date. I then compare that date to the result I would get from just using the LMP.

“If the two dates are within five days of each other, and the pregnancy is less than nine weeks along, then we use the due date calculated by the period, not the ultrasound. But for a greater-than-five-day difference, we use the ultrasound.”

Already had your first ultrasound scan? Then you can use our Due Date by Ultrasound Calculator.

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Find out what you can do with our Health Assistant

While most OB-GYNs use a combination of Naegele’s rule and the pregnancy wheel to determine EDD — and then use an ultrasound to confirm it — there are some other theories and methods about how to calculate due date. However, it’s worth noting that none of the following are currently used by health care providers to work out the due date, as there’s a lack of scientific evidence behind them. The theories are as follows:

How to calculate due date: Mittendorf-Williams rule

One theory on how to calculate due date, also using LMP, is the Mittendorf-Williams rule. This is based on an old study from 1990, and there haven’t been any more recent studies to suggest it’s accurate, which is why health care professionals don’t commonly use it to predict EDD.

This rule is based on a decades-old study that showed that first pregnancies tend to be slightly longer (an average of 288 days from LMP), and for subsequent pregnancies, the delivery date is an average of 283 days from LMP. So …

First, determine the first day of your last menstrual period.
Next, count back three calendar months from that date.
Lastly, add 15 days to that date if it’s your first pregnancy or 10 days if it’s not your first pregnancy.

How to calculate due date: Parikh’s rule

Parikh’s rule is another theory that lacks scientific evidence to back it up, so medical practitioners don’t commonly use it to calculate due date either. The idea goes, however, that it can help predict due date in those who have irregular cycles. So, how does it work?

Loosely designed around Naegele’s rule, the expected date of delivery in Parikh’s rule is calculated by adding nine months to the date of your last menstrual period, subtracting 21 days, and then adding the duration of previous cycles. In short, use this formula:

LMP + 280 days – 21 days + the average length of previous cycles

How to calculate due date: Wood’s rule

Wood’s method considers the individual length of the menstrual cycle, as well as the number of pregnancies a person has experienced. However, there is also minimal research on this and its effectiveness. To work it out …

First, you calculate your expected due date. Do this using the following formulas.
- For first pregnancies: LMP + 12 months – (2 months and 14 days) = EDD
- For subsequent pregnancies: LMP + 12 months – (2 months and 18 days) = EDD
Then, you use the expected due date in the equations below.
- For cycles longer than 28 days: EDD + (actual length of cycle – 28 days) = EDD
- For cycles shorter than 28 days: EDD – (28 days – actual length of cycle) = EDD

How to calculate due date: Conception date

If your cycle runs like clockwork, and you were having sex to get pregnant at a specific time, then you might have an inkling that conception happened on a certain date. But Dr. Celestine says that the conception date “isn’t used medically to calculate due date” because it’s often not accurate.

That makes sense because we know sperm can live in the female body for up to five days, an egg can still be fertilized for up to 24 hours after its release from the ovary, and ovulation doesn’t always happen on the same day each month (you can find out when you’re likely to be ovulating each month using our online Ovulation Calculator). That means you can still get pregnant several days after you’ve had unprotected sex.

How to calculate due date if you’ve had IVF

If you’ve had IVF, then your baby’s due date is calculated slightly differently, depending on:

Whether you had a fresh or frozen embryo transfer
If you had a frozen transfer, the age of the embryo when it was frozen. For example, if it was frozen on day three, then you will be two weeks and three days pregnant on the date of transfer. For embryos frozen on day five, it’s two weeks and five days pregnant on the date of transfer. Your clinic will be able to explain more.

The good news is that IVF due dates are generally more accurate because you’ll know exactly when you had your embryo transfer or medically conceived, although no due date is 100% accurate. Use our IVF Due Date Calculator to work out when you could be due.

How accurate is due date?

There’s a lot that centers around it, so you’re probably wondering how likely it is that you’ll give birth on your due date. “The accuracy of the due date depends on how early in the pregnancy it was calculated and how predictable your menstrual cycle is,” Dr. Celestine explains.

“The earlier you see an OB-GYN to establish care for the pregnancy, the better, because the due date [from an ultrasound scan] is more accurate early in pregnancy compared to later. It’s rare for a baby to be born exactly on their due date [only around 4% of babies are]. Usually, delivery happens within a week before or after. But there are many babies also born prematurely, [along with] medical reasons why you might need to be induced for labor early, so it really depends on the individual.”

What day did I get pregnant?

As Dr. Celestine explains, it’s hard to predict the exact day you got pregnant (unless you’ve successfully conceived after fertility treatment).

“It’s all an estimate because it depends on the day you ovulated,” she says. “If you know your cycle length and it’s always the same, then usually midway through your cycle prior to pregnancy is when conception occurred. ”

Can my due date change?

Lots of people will calculate their due date as one of the first things they do after finding out they’re pregnant. And that’s useful for having a rough idea of when your baby will arrive, but it’s worth noting that this should be confirmed by your health care provider. They will use information about your last menstrual period, plus your first ultrasound, to work out your EDD, and once this has been calculated, it’s rare for your due date to change.

It’s so unusual for the due date to change after your first ultrasound scan because knowing the gestational age holds a lot of importance in monitoring the health of a pregnancy. “There are certain tests that need to be performed at certain gestational ages during a pregnancy,” Dr. Celestine explains. “Knowing how far along you are is also important for following the growth of the baby, when we can expect to deliver, and much, much more.”

Can I plan my due date?

Some people like to be organized, and there’s nothing wrong with that. But it can be quite tricky to plan a due date because there are so many factors at play with conception that you (and your partner) don’t have control over.

Nobody ever knows for certain when they will conceive. Even if you pinpoint your fertile window and have plenty of unprotected sex during that time, you still won’t know for certain whether or not that will be the month you get pregnant. That’s because so much of it is up to chance. For context, 45% of young couples (under 35) will conceive after three cycles, and 65% will get pregnant after six cycles. So while you might want to plan to have a baby in a certain month, all you can really do is try.

And even if you do manage to conceive at a time that gives you your ideal due date, remember that your EDD is just an estimate. Babies come on their own schedule. While the “average” pregnancy lasts 40 weeks from the day of the last menstrual period, it is normal for babies to come anywhere from 37 to 42 weeks, so it’s best not to focus too much on a specific due date.

Due date tracking with Flo

Whether you’re currently pregnant or trying to work out when you’d be due if you got pregnant today, Flo can help. Use our Trying to Conceive mode to optimize your chances of getting pregnant by tracking your periods, which can help to identify your most fertile days. Alternatively, switch to Pregnancy Mode to get week-by-week updates for both your body and your baby.

Try some of Flo's other online tools, including our hCG calculator, our pregnancy test calculator, and our period calculator.

References

“Extremely Preterm Birth.” The American College of Obstetricians and Gynecologists, www.acog.org/womens-health/faqs/extremely-preterm-birth. Accessed 30 Aug. 2022.

“Heavy and Abnormal Periods.” The American College of Obstetricians and Gynecologists, www.acog.org/womens-health/faqs/heavy-and-abnormal-periods. Accessed 30 Aug. 2022.

“How Long Does Pregnancy Last?” The American College of Obstetricians and Gynecologists, www.acog.org/womens-health/experts-and-stories/ask-acog/how-long-does-pregnancy-last. Accessed 13 July 2022.

Jukic, A. M., et al. “Length of Human Pregnancy and Contributors to Its Natural Variation.” Human Reproduction, vol. 28, no. 10, Oct. 2013, pp. 2848–55.

Khedri, Parichehr, et al. “Comparison of the First Trimester Ultrasound and Parikh’s Formula in Determining the Expected Date of Delivery: A Prospective Study.” BMC Pregnancy and Childbirth, vol. 21, 30. Apr. 2021, jbrms.medilam.ac.ir/article-1-152-en.pdf.

Mittendorf, R., et al. “Predictors of Human Gestational Length.” American Journal of Obstetrics and Gynecology, vol. 168, no. 2, Feb. 1993, pp. 480–84.

Morgan, John A., and Danielle B. Cooper. “Pregnancy Dating.” StatPearls, StatPearls Publishing, 2021.

“Screening Tests in Pregnancy.” NHS, www.nhs.uk/pregnancy/your-pregnancy-care/screening-tests/. Accessed 13 July 2022.

How to correctly calculate the gestational age and determine the date of delivery

It often comes as a surprise to first-time pregnant women that in obstetrics the gestational age is determined not in months, but in weeks. But the surprises do not end there - the fact is that the obstetric period is calculated not from conception, but from the first day of the last menstruation.

In fact, pregnancy occurs two weeks after the start of the obstetric period, at the time of ovulation, when the sperm meets the egg. Thus, the age of the embryo, or gestational age, differs from the obstetric one by 2 weeks down.

How long does pregnancy last?

The obstetric term of a term pregnancy is 40 weeks, or 280 days. It is on the basis of the obstetric gestational age that the doctor will prescribe tests and examinations for you, determine the date of maternity leave and calculate the EDD (estimated date of birth).

Doctors use the Negele formula to calculate the EDD. According to this formula, if we add nine months and seven days to the first day of the last menstruation, we get the estimated date of birth.

Unfortunately, determining the gestational age from the first day of the last menstrual period is not a very accurate method. It is well suited for women with a stable 28-day cycle, but if your cycle is slightly longer or shorter, then the date of ovulation shifts, respectively, and the actual obstetric gestational age will differ from the established one.

The most accurate way to calculate the EDD is to add 266 days to the date of the last ovulation (if you know it).

How to confirm pregnancy, determine the duration of pregnancy and the date of delivery

By itself, a delay in the start of a new menstrual cycle does not necessarily indicate pregnancy - failures can be explained by diseases, excessive physical exertion or stress. Pregnancy must be confirmed with an hCG test or examination on a gynecological chair. 1) Blood test for hCG cycle or the woman will feel the first symptoms. Also, an analysis of the level of hCG in the blood allows you to determine the gestational age with an accuracy of about two weeks.

2) Home pregnancy test

Home pregnancy tests also work by measuring hCG levels, but they are less sensitive than blood tests. The most modern of them can not only confirm the presence of pregnancy a few days before the delay, but also indicate (not too accurately) an approximate date.

Tests of the old generation will show a more or less accurate result only after a delay, that is, after 2-4 weeks from conception.

3) Gynecological examination

A qualified gynecologist-obstetrician can diagnose pregnancy during an examination starting 3-4 weeks after conception, focusing on changes in the shape and size of the uterus, as well as other signs.

4) Ultrasound

Ultrasound is the most accurate way to diagnose pregnancy. With the help of ultrasound with a transvaginal sensor, it is possible to determine the presence of a fetal egg in the uterus already 1-2 weeks after conception (3-4 obstetric weeks), but fetal heartbeats can only be detected for a period of 5-6 obstetric weeks. It is possible to determine the gestational age with high accuracy (up to 2-3 days!) With the help of ultrasound only from 6-7 weeks.

If the delay, as well as the result of an hCG test or blood test, indicate that you will soon become a mother, do not rush to get an ultrasound right away. Wait another 2-3 weeks, then by ultrasound you will not only be accurately determined by the period, but will also be allowed to listen to the baby's heartbeat.

If you did not do an early ultrasound to confirm pregnancy, then for the first time you will encounter this study at the 10-14th week. At the same time, the exact gestational age and PDR will be established or corrected for you. During pregnancy, you will need to undergo such an examination at least twice more. This will happen at 20-24 and 30-34 weeks. However, it is worth saying that ultrasound in the 2nd and 3rd trimesters may have an error in determining the gestational age. The PDR established according to them may differ from the real one by 2-3 weeks. That is why it is so important not to miss the first screening and do an ultrasound on time.

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Gestational age. Date of birth. Calculate gestational age and due date

CONTENTS

What is a calculator?
How does a calculator work?
Other ways to determine and confirm the due date.
How accurate is the calculator?

What is a calculator?

In most cases, women do not know the exact date of conception, but they can with great certainty to say when the last menstrual cycle began. The first the day of the last menstruation is the starting point. Well, then 9 comes into play0135 pregnancy calculator - a program that makes a lot of calculations for you and answering almost all questions of interest to the expectant mother :

when was the conception approximately;
what is the estimated date of delivery;
what is the exact week now and how much is left before the birth;
how a child develops, what size it is, what it already does in the womb and what skills it has.

Calculator free, always available online, easy to use, has concise and understandable interface, will not let you make arithmetic errors and displays results in a visual and interesting way. In addition, you can always check the accuracy calculator, independently making calculations according to well-known obstetric techniques, which we present below.

To calculate the gestational age and expected date of delivery, a woman needs to enter in the calculator, only the date of the first day of the last menstruation (LPM) in the format "day month Year". If you enter the last day of your period or a known date conception, the calculator will show completely different results, you need to enter exactly the start date last menses.

The calculator calculates the obstetric period - this is when the first day of menstruation is considered like the first day of pregnancy. It is by obstetric term that gynecologists track the development fetus, prescribe tests and examinations.

The gestational age in the calculation results of the calculator is shown in weeks, this is the most simple and convenient interval. There are other generally accepted intervals for dividing such a large period - months (10 lunar months of 28 days) and trimesters. The trimesters divide the process intrauterine gestation into three phases of 13 weeks each.

The results display the exact period in weeks and days, a brief description of the development of the fetus, the height and weight for the calculated week are indicated, which organs are being formed, what can already be felt and do baby. A link is provided to the full article with colorful illustrations, telling about the condition of the fetus and mother, tests and examinations, recommended diet, possible problems and ways to overcome them. You will always know what to prepare for.

This calculation displays both fetal ages: the so-called "gestational" fetal age (menstrual), which is different from the so-called "ovulation" age (fertilization), it is two weeks less and is counted from the estimated date of conception. Therefore, all the details fetal development and well-being of women are considered from week to week, starting precisely from the third week.

In addition, you will know how many days are left before childbirth, under what sign of the zodiac and in what year of the Chinese calendar your baby will be born, by clicking on additional links you can determine the color of the eyes, the blood type of the child.

Depending on the week, additional links are displayed to calculators for checking ultrasound results, hCG hormone levels, blood test results, weight gain rates. If you wish, you can calculate an individual calendar of analyzes and examinations, both for mother and child.

Starting in the second or third trimester, you can find out about your benefits and calculate your benefits. amounts. For working mothers, it is possible to determine the date of maternity leave and find out if you are entitled to annual leave leave before the decree.

Whatever week you are, the calculator will offer you to test your knowledge using interactive tests "Care of a newborn", "Feeding of newborns", "Tests and examinations of pregnant women", "Rights of pregnant women". You will just have time to fill in the gaps and improve your knowledge on these important topics.

The calculator will also calculate the estimated date of conception of the child, according to which, using Chinese gender calendar, you can find out who you will be - a girl or a boy. According to the results of the ultrasound, it will be interesting to know whether the prediction came true.

How does a calculator work?

All calculations of our calculator are based on the obstetric calculation method, as the most accurate, scientifically based and universally accepted method for calculating gestational age. other methods, for example, a report from the day of intercourse or from ovulation cannot be considered reliably accurate due to the characteristics of the reproductive system.

The length of the cycle may differ for different women, one has 21 days, the other has 34, moreover, in the same woman, the cycle may be irregular and fluctuate in duration during years for various reasons. On average, most women have a menstrual cycle is 28 days.

But one thing is common to all: conception of a child is possible only during ovulation - if there is no mature egg, then conception will not occur.

At the beginning of the cycle, a follicle forms on the surface of the ovary, inside which the female matures. sex cell. In the middle of the cycle, the follicle sac ruptures under the influence of strictly defined hormones. and allows spermatozoa access to the oocyte.

After ovulation, the female gamete lives from 24 to 36 hours, at which time conception must occur, otherwise the cell dies. This process is repeated every cycle.

It turns out, regardless of the length of the cycle, nature allocates only one or two days for the process of conception. However, this does not mean that sexual intercourse can lead to pregnancy only during the hours when the oocyte lives. Not, due to the ability of spermatozoa to survive for a long time in the female body, sex even 3-4 days before release the egg can lead to fertilization immediately after its release from the follicle. With active sexual life in general it is impossible to determine whether sexual intercourse before, during or after ovulation led to conception.

Therefore, in obstetric practice, it is generally accepted that conception occurs during the period of ovulation - 14 days before before the end of the menstrual cycle. And again, we are faced with a harsh reality here - a woman ovulates can happen both earlier and later than the above day. Based on all this, it is customary to count from the date of the last menstruation, this is both easier, and the woman usually remembers this date.

Thus, according to the obstetric standard, the first day of the last menstruation is the first day pregnancy, and the day of conception falls approximately at the end of the second week. If a woman finds out about the delay, then this is already the 4th week and the gynecologist, regarding a week-long delay, is already setting a deadline of 5 weeks.

Our online calculator is based on this obstetric method. Weeks are normal calendar months, and obstetric months, each of them has exactly 4 calendar weeks.

Pregnancy lasts an average of 40 weeks or 10 obstetric months , in calendar days this is good well-known 9 months . 1 2 3 4 5 6 0219 8 9 10 11 12 13 14 15 16 17 18 19 20 II 21 22 23 24 25 26 27 28 29 30 III 31 32 33 34 35 36 37 38 39 40

and the fetus, each trimester has its own characteristics.

For example, in the first trimester there is a rapid the formation and development of the organs of the child, then miscarriages most often occur. In the third trimester it is necessary to prepare for the manifestation of possible problems associated with pregnancy - hypertension, toxicosis.

There are 3 calendar months in one trimester, the first trimester is 1-13 weeks, the second trimester is 14-27 weeks, the third is 28-42 weeks .

1st trimester

2nd trimester

3rd trimester

or all three ways:

Add the average duration of pregnancy, which is 280 days, to the first day of the last menstruation.
Add 9calendar months to the first day of the last menstruation and subtract 7 days from the resulting date.
Subtract three months from the first day of your last period and add 7 days to the result.

Absolutely the same time is considered in the antenatal clinic, the same methods are used in round paper obstetric calendars.

Other ways to determine and confirm the due date

There are no other scientific methods for determining the gestational age and due date. But there are methods using which can be confirmed or corrected. Again, almost all of them are based on the obstetric method, statistical data and data from an objective examination of the expectant mother.

The main objective sign of pregnancy is an increase in the size of the uterus, which in the first months is determined by vaginal examination, and after the third - by the height of the fundus of the uterus. By the end 1st month (28 days) the uterus corresponds to the size of a chicken egg, 2nd month (56 days) - an average fist women, then each month has its own size. There is no need to talk about the accuracy of this method.

Additional information about the due date and due date can be obtained by measuring the length of the fetus. measurements produce a tazomer in the position of a woman lying on her back. One button of the tazomer is placed on the lower pole head, the second - at the bottom of the uterus. Calculations are made using a special formula, but the result is also approximate due to different assumptions, for example, the thickness of the abdominal walls can be taken in both 3 and 5 cm.

According to the level of hCG

At the earliest stages (from the 4th to the 8th week), pregnancy is confirmed by the level of hCG. By date of conception or, if it is unknown, then the obstetric period is determined from the first day of the last menstruation, and from it the hCG rate is determined. If the pregnancy is proceeding normally, then the hormone levels will correspond, or rather be within the range of valid values. The accuracy of this method is very low, as hormone levels are indicated in a wide range and the main thing for which this method is used is to determine the normal development fetus. The hCG level may not fall within acceptable limits, but if it doubles in two days, the fetus is considered to be developing normally. As you can see, this method is not always possible to use.

Ultrasonography

Ultrasound examination can also confirm pregnancy, this method is used to detect fetal egg and registration of heartbeats. Ultrasonography is currently the only method allowing with the greatest degree of accuracy to establish the gestational age and follow the development of the fetus, starting from the very first weeks of its intrauterine development.

The date of the last menstruation is entered into the ultrasound machine and, upon further scanning, the doctor determines how embryonic development corresponds to the obstetric term. Statistical tables of sizes are set in these devices fruit for each week and day.

In early pregnancy, when embryos develop at about the same rate, it is easier to compare their sizes are with average statistical norms and it is possible to more accurately determine the age. In this case, the doctor evaluates parameters of the baby, compares with the tables, gets the gestational age and, after adding two weeks, calculates obstetric term. If a woman did not remember the start date of the last menstruation, then the only way to determine the date pregnancy.

Later, when the fetus begins to develop according to its individual genetic program laid down by the parents (large or petite build, large or small height), it becomes more difficult to accurately determine the week.

By movements

In the middle of pregnancy, usually at 20 weeks in nulliparous women and at 18 weeks in multiparous women first fetal movement. Before the advent of ultrasound, this method was used without alternative to confirm the term pregnancy, there was no other way. Now this is an auxiliary method, it cannot be considered exact, since not everyone is able to recognize the first stirring. Currently no longer used for its intended purpose.

How accurate is the calculator?

The same as the calculator method for calculating the gestational age used by an obstetrician-gynecologist in a women's consultations, in a hospital for conservation, in a maternity hospital, in medical equipment - ultrasound machines and laboratory equipment.

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