How to calculate your due date in pregnancy

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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Home pregnancy tests: How to take a pregnancy test at home

Home pregnancy tests work by detecting the presence of a hormone called hCG in your urine. Some at-home pregnancy tests claim they're sensitive enough to give a positive result as early as five days before your next period. But you're more likely to get an accurate result (and avoid a false negative) if you wait until the first day of your missed period.

How do home pregnancy tests work?

All home pregnancy tests measure the amount of a specific hormone known as human chorionic gonadotropin (hCG) in your urine. When the embryo starts to implant in the lining of your uterus, as early as six days after conception, cells that will later develop into the placenta begin to produce hCG.

As the placenta grows, the amount of hCG in your body doubles every two days or so during the first few weeks. When hCG levels are high enough, the hormone enters the bloodstream. That's when it starts to show up in the blood and urine. If the home pregnancy test detects enough hCG in your urine, it gives you a positive result.

Some tests are more sensitive than others. But in general, it's easier for any home pregnancy test to pick up hCG in the urine when you're 4 weeks pregnant (when there's more hCG) versus 6 days after fertilization (when there's a trace amount of hCG at best).

The best way to tell if a test is sensitive enough to pick up the smaller amounts is to read the fine print. Some urine pregnancy tests can detect lower levels of hCG. If you're wanting to test early, before you miss a period, check the package insert to learn more about how much hCG needs to be present in your urine to detect a pregnancy.

How to use an at-home pregnancy test

For best results when using a home pregnancy test:

Make sure the test is up to date. Check the expiration date on the package, especially if you've had it for a while. If you've been storing the test in the bathroom, the humidity may have ruined it. Better to throw it away and get a new one.
Test first thing in the morning. Your urine is most concentrated when you first get up. If you're pregnant, hCG levels will be higher too. That makes it easier for the at-home test to spot it.
Read the directions carefully. Different brands have different instructions. With some home tests you urinate in a cup and then use the dropper to place a small sample in the testing well. With others, you can pee directly onto the strip or stick. And some let you do either.
Wait 5 minutes to check. You get the most accurate results if you wait up to 5 minutes, though this can vary by brand. Read the package instructions to learn exactly how long you'll need to wait to confirm a negative or positive result.

Different tests reveal the results in different ways too. Some show pink or blue lines on the test strip, while others have a red plus or minus sign in a window. Digital tests give results in words ("You're pregnant"). Most have a control indicator (often a second line or symbol) that tells you whether the test is valid.

If the control indicator doesn't show up properly, the test is probably faulty. If this happens, call the manufacturer and see if they'll send you a new one. Also call the company if you have questions about how to use the test.

If the test shows a negative or a faintly positive result, wait another few days and try again if you still haven't gotten your period. Maybe you ovulated later in your cycle than you thought and took the test too early to get a positive result.

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One negative result doesn't necessarily mean you're not pregnant. Every woman produces different amounts of hCG and it's not even the same for each pregnancy. If you suspect that you're pregnant (say, you're having early pregnancy symptoms) and still have a negative test, take another home pregnancy test in a week if you still haven't gotten your period.

If you still haven't gotten either your period or a positive result two weeks or so after you would expect it, reach out to your provider.

When can I take an at-home pregnancy test?

At-home pregnancy tests are getting better and better. But you're still more likely to get the most accurate results if you wait to take a pregnancy test until the morning of your expected period. Waiting a few more days after that may provide an even more accurate result.

Some home pregnancy tests claim they're sensitive enough to give you a positive result as early as five days before your next period. And some women will have produced enough hCG to get a positive result at that point. But, once again, every pregnancy is different.

If you're eager (or anxious) to know if you're pregnant, go ahead and do the test 10 or 12 days after you think you've conceived. If you get a negative result, no problem. Wait a week and test again if you still haven't gotten your period.

How accurate are home pregnancy tests?

At-home pregnancy tests are 99 percent accurate. But you can still get what are called false negatives or false positives.

A false negative is when you're pregnant but the test results show up negative. Sometimes you get a faint line on the home pregnancy test, so the result is unclear. These things usually happen if you take the test too soon, before your hCG levels are high enough. If you get a faint line on a pregnancy test, wait a few days and test again.

A false positive pregnancy test means that you get a positive result but aren't pregnant. This doesn't happen very often, except for in the following circumstances:

You've had a miscarriage or terminated a pregnancy in the past eight weeks, or have a molar pregnancy.
You've taken a fertility drug with hCG (used to induce ovulation in fertility treatments).
You have a rare medical condition, such as an hCG-secreting tumor.
You're using an expired or faulty test.
You're going through perimenopause or menopause.

If you have a positive result and then get your period soon after, you may have had what's called a chemical pregnancy. This means the embryo implanted in your uterus and developed just enough to start producing detectable levels of hCG, but then it stopped developing. This is most commonly caused by a genetic abnormality of the embryo.

An ectopic pregnancy can also result in a positive pregnancy test, even though these pregnancies often show slower rises in hCG.

No matter what result you get from a pregnancy test, call your healthcare provider right away if you:

Feel dizzy or faint
Have abdominal pain (especially a sharp or stabbing pain in your abdomen or on one side of your pelvis
Have abnormal bleeding

These could be signs of a miscarriage or ectopic pregnancy.

What to do if you get a positive home pregnancy test

Some women take more than one home pregnancy test (or several) just to be sure – but that's not really necessary. Once you've gotten a positive pregnancy test, call your healthcare provider to set up a prenatal visit or to discuss your options if you're not sure about continuing the pregnancy.

If you don't already have a family doctor, ob-gyn, or midwife who can provide prenatal care, do some research to see who's covered by your insurance, and ask for recommendations.

Doctors typically schedule the first prenatal visit when you're about 8 weeks pregnant. But some providers will see you sooner, especially if you have a medical condition or have had problems with a pregnancy in the past. It's especially important to see your provider sooner if you're having nausea and vomiting, vaginal bleeding, or abdominal pain.

Will you need a blood test to confirm your pregnancy?

Not necessarily. To make sure you're pregnant, most healthcare providers use a urine pregnancy test, just like your at-home pregnancy test . But your provider may use a blood test instead. Just note: It may take anywhere from an hour to a day or more to get the results.

There are two types of pregnancy blood tests:

A qualitative hCG blood test just shows whether there is hCG in your blood. The results return as "positive" or "negative." You usually get the results in about the same time you would with a urine test.
A quantitative blood test (beta hCG test or serum test) measures the exact amount of hCG in your blood. The results return as a number. This test is very accurate. It can detect hCG as early as six to eight days after ovulation, or about a week before your period is due. It takes longer to get results from a quantitative blood test, though.

Again, your provider may not give you a blood test. Oftentimes, a positive home pregnancy test is enough to get started with the prenatal care you need.

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.