How to determine the due date of a baby

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

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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.

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When does a baby have a heartbeat? When you can hear or see the heartbeat.

You may be able to see the beating of cells in the heart tube for the first time when you're about 6 weeks pregnant if you have an early ultrasound exam.

If you don't have a first-trimester ultrasound, you'll probably first hear your baby's heart with a handheld Doppler at a regular prenatal visit.

Your caregiver may be able to find cardiac activity with a handheld Doppler as early as 10 weeks, but the timing depends on a number of factors, including the position of your uterus, your belly shape, and how full (or empty) your bladder is.

When does a baby have a heartbeat?

At 5 to 6 weeks of pregnancy, there's a flickering of cells within the embryo's torso. This flickering is the developing heart tube.

At this point, the heart isn't the four-chambered organ we're familiar with. It's a tube-shaped structure that has a lot of developing to do. The heart tube bends and twists to eventually form the heart, including its chambers.

Because the heart isn't yet developed, the American College of Obstetrics and Gynecologists (ACOG) defines this movement as "cardiac activity" rather than a heartbeat.

"What pregnant people may hear or see is the ultrasound machine translating electronic impulses that signify fetal cardiac activity into the sound that we recognize as a heartbeat," ACOG states. The group recommends waiting until the heart is fully formed before using the term "heartbeat."

A baby's heart is one of the first structures to form, because it's needed to deliver oxygenated blood and nutrients to other developing organs.

Some of the important steps in heart development are:

The heart tube twists and bends into an S shape, and the bottom of the tube moves up to form the two upper heart chambers (atria).
The middle of the tube forms the two lower chambers (ventricles).
Walls form to divide the chambers, each with an entrance and exit for blood flow.
Valves form between the ventricles and the aorta (large blood vessel) and pulmonary artery.
At about 10 weeks to 12 weeks, the heart is formed.
Small blood vessels form and fill with blood.
At birth, the opening between the two atria closes. Your baby is now getting oxygen from their lungs and not from the placenta.

What does a fetal heartbeat sound like?

Many women say that the beating of their baby's tiny heart sounds like galloping horses. The embryonic and fetal heartbeat is fast, about 110 to 160 beats per minutes.

If you hear a whooshing noise, that's not the heartbeat – it's probably because of movement or the monitor traveling past your placenta. Also, if you hear two heartbeats, don't assume you're having twins. You're likely hearing your own heartbeat in the background.

If the heart rate of the embryo or fetus is healthy, it's a sign that development is progressing normally. The chances of a miscarriage once you see or hear a heartbeat are less than 10 percent (at 6 weeks) and less than 1 percent at 9 weeks.

What if my provider can't detect a heartbeat?

If your doctor or midwife doesn't find your baby's heartbeat on your first-trimester ultrasound right away, it could be because:

It's too early in your pregnancy. Your due date may be off. (This can happen, especially if your menstrual cycle was irregular.) Your provider will schedule another visit in a week or two.
You have a retroverted uterus. Because of the position of your uterus, the baby can be just a little further away and harder to detect.
You're overweight. Extra padding between the ultrasound wand and the baby may make it harder to detect the heartbeat.
Miscarriage. If there's no heartbeat when expected (and ultrasound measurements confirm the age) or if cardiac activity was detected and now isn't, this may be a sign of miscarriage.
Ectopic pregnancy. In this case, an ultrasound wouldn't pick up heart motion in the uterus because there's no embryo there. Although ectopic pregnancies are never viable, they can sometimes develop enough to have heart motion. An ectopic pregnancy is a surgical emergency that can be fatal if not treated quickly.

How will I usually hear my baby's heartbeat?

Your provider will check your baby's heart rate with a fetal Doppler (a handheld ultrasound monitor) at each prenatal visit after about 10 weeks.

The procedure is completely painless. Your doctor or midwife will cover the device with ultrasound gel and move it around on your belly until they find a spot where the heartbeat can be detected. The Doppler sends and receives sound waves that safely bounce off your insides, including your baby's heart. The returning sound waves are processed and amplified by the device so you and your provider can hear the heartbeat.

You can rent or buy a Doppler for home use. However, some experts think a home Doppler isn't a good idea.

That's because it can take considerable training and practice to find and correctly identify a baby's heartbeat. You may not be able to hear the heartbeat – not because of an issue with your baby, but due to user error. It's also possible to hear the sound of blood flowing through the placenta or your own blood vessels and mistake it for a heartbeat.

There are better ways to monitor your baby, such as paying attention to your baby's movements and attending all of your prenatal appointments.

Learn more:

When will my pregnancy start to show?
Pregnancy in weeks, months, and trimesters

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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. nine0003

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. nine0003

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 nine0007

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. nine0003

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. nine0003

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. nine0003

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. nine0003

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How to calculate due date. Calculate gestational age by week

Our online pregnancy calculator will help you calculate gestational age by week and find out when your baby is due

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Calculate the due date

It is impossible to calculate the due date with absolute accuracy. The estimated day of delivery is calculated as follows: the first day of the last menstruation + 280 days . This is an average date, usually delivery occurs in the next plus or minus 10 days . Learn more about the calculation of the PDR.

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How to calculate due date

What is EDD?

EDD is an abbreviation commonly used by physicians for the phrase "estimated due date".

How is the expected date of delivery (ED) determined?

How to calculate the due date correctly? Pregnancy from conception to the birth of a child lasts about 266 days, or 38 weeks. Since the date of conception, as a rule, is not exactly known, in modern obstetrics it is customary to calculate the gestational age from the first day of the last menstruation, i.e. you need to calculate the date of birth by menstruation. With this calculation, it is approximately 280 days, or 40 weeks, since ovulation and, accordingly, fertilization usually occur two weeks after the start of the cycle. Ultrasound equipment is also set up for the same calculation of the gestational age, therefore, if menstruation is delayed by 4 weeks, the doctor will most likely report 8 weeks of pregnancy (whereas only about 6 weeks have passed from the moment of conception). nine0003

Accuracy of due date calculation

How to calculate exact gestational age? You can calculate the approximate date of birth of a child if you know the date of the last menstrual period. The estimated due date (EDD) will be 280 days (40 weeks) after the first day of your last period. However, only 5% of children with normal pregnancies are born on the “calculated” day, another 85% are born within a period of plus or minus a week from this date, and another 10% are “late” or “hurry” for another week. It is believed that a healthy pregnancy can last from 38 to 42 weeks. nine0003

Duration of pregnancy

How to correctly calculate the duration of pregnancy? The duration of pregnancy depends on many factors, including the individual pace of development of the child, as well as the duration of the woman's menstrual cycle. So, for example, if the cycle duration is less than 24 days, then childbirth can occur 10-15 days earlier than when calculated according to the formula "1st day of the last menstruation + 280 days", while the child will be fully mature and healthy. And if the menstrual cycle lasts more than 32 days, then the pregnancy can drag on for 10-15 days, and this will not be considered overdose.