How to calculate edd from last menstrual period

How to Calculate Your Due Date

Pregnancy lasts an average of 280 days (40 weeks) from the first day of your last menstrual period (LMP). The first day of your LMP is considered day one of pregnancy, even though you probably didn’t conceive until about two weeks later (fetal development lags two weeks behind your pregnancy dates).

Read our report on the 13 best pregnancy iPhone and Android apps of the year here.

Calculating your due date isn’t an exact science. Very few women actually deliver on their due date, so, while it’s important to have an idea of when your baby will be born, try not to get too attached to the exact date.

If you have regular 28-day menstrual cycles, there are two ways to calculate your due date.

Naegele’s rule

Naegele’s rule involves a simple calculation: Add seven days to the first day of your LMP and then subtract three months.

For example, if your LMP was November 1, 2017:

1. Add seven days (November 8, 2017).
2. Subtract three months (August 8, 2017).
3. Change the year, if necessary (to the year 2018, in this case).

In this example, the due date would be August 8, 2018.

Pregnancy wheel

The other way to calculate your due date is to use a pregnancy wheel. This is the method that most doctors use. It’s very easy to estimate your due date if you have access to a pregnancy wheel.

The first step is locating the date of your LMP on the wheel. When you line up that date with the indicator, the wheel displays your due date.

Remember that the due date is only an estimate of when you will deliver your baby. The chances of actually having your baby on that exact date are very slim.

This is more common than you’d think. Luckily, there are ways to figure out your due date when you can’t remember the first day of your LMP:

• If you know you had your LMP during a particular week, your doctor can estimate your due date accordingly.
• If you have no idea when your last period was, your doctor may order an ultrasound to determine your due date.

Some women have cycles that are consistently longer than the average 28-day cycle. In these cases, a pregnancy wheel can still be used, but some simple calculations are necessary.

The second half of a woman’s menstrual cycle always lasts for 14 days. This is the time from ovulation to the next menstrual period. If your cycle is 35 days long, for example, then you probably ovulated on day 21.

Once you have a general idea of when you ovulated, you can use an adjusted LMP to find your due date with a pregnancy wheel.

For example, if your menstrual cycle is usually 35 days long and the first day of your LMP was November 1:

1. Add 21 days (November 22).
2. Subtract 14 days to find your adjusted LMP date (November 8).

After you calculate your adjusted LMP date, simply mark it on the pregnancy wheel and then look at the date where the line crosses. That is your estimated due date.

Some pregnancy wheels may allow you to enter the date of conception — which occurs within 72 hours of ovulation — instead of the date of your LMP.

Your doctor may change your due date if your fetus is significantly smaller or larger than the average fetus at your particular stage of pregnancy.

Generally, your doctor orders an ultrasound to determine the gestational age of your baby when there’s a history of irregular periods, when the date of your LMP is uncertain, or when conception occurred despite oral contraceptive use.

An ultrasound allows your doctor to measure the crown-rump length (CRL) — the length of the fetus from one end to the other.

During the first trimester, this measurement provides the most accurate estimation for the age of the baby. Your doctor may change your due date based on the ultrasound measurement.

This is most likely to occur in the first trimester, especially if the date estimated by the ultrasound differs by more than one week from the date estimated by your doctor based on your LMP.

In the second trimester, an ultrasound is less accurate and your doctor probably won’t adjust your date unless the estimates vary by more than two weeks.

The third trimester is the least accurate time to date a pregnancy. Estimates based on an ultrasound can be off by as much as three weeks, so doctors rarely adjust dates during the third trimester.

However, it’s not uncommon for a doctor to perform an ultrasound in the third trimester if they’re thinking about changing your date.

A repeat ultrasound provides valuable information about the growth of the fetus and may reassure you and your doctor that the change in due date is reasonable.

Ultrasound measurements for estimating the age of a fetus are more accurate during the early stages of pregnancy. In the first few weeks, fetuses tend to develop at the same rate. However, as pregnancy progresses, the rates of fetal growth begin to vary from pregnancy to pregnancy.

This is why ultrasound measurements can’t be used to accurately predict the age of the baby in the later stages of pregnancy.

Ultrasounds are not a necessary part of prenatal care. Avoid numerous scansTrusted Source and have ultrasounds for medical reasons only.

When a doctor performs an ultrasound, they write a report on the findings and include two estimated due dates. The first date is calculated using the date of the LMP. The second date is based on the ultrasound measurements. These dates are rarely the same.

When your doctor evaluates the ultrasound results, they’ll determine whether or not these dates are in agreement. Your doctor probably won’t change your due date unless its significantly different from your ultrasound date.

If you have more ultrasounds, each ultrasound report will contain a new due date based on the most recent measurements. An expected due date shouldn’t be changed based on measurements from a second- or third-trimester ultrasound.

Due date estimations are more accurate earlier in pregnancy. Later ultrasounds are helpful in determining whether the fetus is growing well but not for determining the age of the fetus.

Learn more about how your body changes during your pregnancy.

• ACOG reinvents the pregnancy wheel: Launches new due date app. (2016). https://www.acog.org/About-ACOG/News-Room/News-Releases/2016/ACOG-Reinvents-the-Pregnancy-Wheel
• Avoid fetal “keepsake” images, heartbeat monitors. (2014). https://www.fda.gov/ForConsumers/ConsumerUpdates/ucm095508.htmTrusted Source
• Calculating a due date. (n.d.). http://www.hopkinsmedicine.org/healthlibrary/conditions/pregnancy_and_childbirth/calculating_a_due_date_85,P01209/
• Calculating your estimated due date. (2014). https://my.clevelandclinic.org/health/diseases_conditions/hic_Am_I_Pregnant/hic_Calculating_Your_Estimated_Due_Date
• Due date calculator. (n.d.). http://www.marchofdimes.org/pregnancy/calculating-your-due-date.aspx
• Pregnancy due date and gestational age calculator. (n.d.). http://www.perinatology.com/calculators/Due-Date.htm

Pregnancy due date calculator - 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

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Week 11

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Week 12

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Week 13

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Week 14

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Week 15

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Week 17

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Week 20

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Week 22

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Week 23

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Week 25

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Week 30

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Week 31

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Week 32

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Week 33

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Week 34

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Week 35

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Week 36

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Week 37

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Week 38

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Week 39

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Week 40

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Week 41

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Week 42

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Medically reviewed by

Dr. Barbara Levy

Clinical professor of obstetrics and gynecology, George Washington University School of Medicine and Health Sciences, UCSD Health, California, US

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.

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).

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.

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.

“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.

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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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:

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.

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

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

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.

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.

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.”

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. ”

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.”

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.  

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. 

Updated April 02 2023

〚 Pregnancy calculation. How to determine the date of birth? 〛Babystart Official Dealer

Feb 11, 2020

Most pregnancies last around 40 weeks (or 38 weeks from conception), so generally the best way to determine your due date is to count 40 weeks or 280 days from the first day of your last period ( LMP). Another way to do this is to subtract three months from the first day of your last period and add seven days. So if your last period started on April 11th, you would count down three months to January 11th and then add seven days, which means your due date should be January 18th. This is how your doctor will estimate your due date - and that's a pretty solid goal. But remember: delivering a week or two before or after is just as normal.

Date of conception

Calculating due date based on the first day of your last period works well for women with relatively regular menstrual cycles. But if your cycle is irregular, the LMP method may not work for you. Because a reliable estimated due date (EDD) is important, you and your doctor can use your conception date if you remember it. Just add 266 days to get an estimate.

IVF transfer date

According to the Centers for Disease Control and Prevention (CDC), more than 250,000 assisted reproductive technology cycles are performed each year in the United States, resulting in about 77,000 or more babies born each year. If you are part of a growing tribe of IVF moms, you can more accurately calculate your due date using the IVF transfer date.

Ultrasound Scan

Even if you can't pinpoint when you conceived, forgot the day of your last period, or aren't sure when you ovulated, other clues can help you and your doctor determine your due date at your first pregnancy appointment, including :

Early ultrasound, which can more accurately determine the date of pregnancy. However, keep in mind that not all women get an early ultrasound. Some practitioners do them regularly, but others recommend only one if your periods are irregular, you are 35 or older, you have a history of miscarriage or pregnancy complications, or the due date cannot be determined based on your physical examination and LMP.

Pregnancy milestones, such as the first time the baby's heartbeat is heard (around 9 or 10 weeks, although this may vary) and when you first feel the baby move (between 18 and 22 weeks on average, but this may be earlier or later) may give clues as to whether your due date is accurate.

Your fundal height, which is measured from your pubic bone to the top of your uterus, is checked by your doctor at every prenatal visit and helps confirm your due date.

The size of your uterus, which will be noted during your initial internal pregnancy test, can also be a factor in determining EDD.

Can I schedule my due date?

Whether you're trying to avoid a midsummer pregnancy or you're a teacher who wants to have the most fun with your baby, you can try to determine when you'll get pregnant to "plan" your due date. But even if you're one of those lucky ones who can get pregnant when she really wants to, just remember that you probably won't be able to pinpoint exactly when you'll give birth a day (or even a week). or a month!)

Can the due date change a lot?

Yes, your due date may change. While this is definitely not a cause for concern, your doctor may change your due date for a number of reasons as your pregnancy progresses. Maybe you're having irregular periods and an early ultrasound date was cancelled, or that your first ultrasound was in your second trimester. It may also be because you have abnormal growth or abnormal levels of alpha-fetoprotein (AFP), a protein produced by your baby. Talk to your practitioner if you have any questions or concerns.

How to calculate (determine) the gestational age and date of delivery?

Is it possible to calculate the exact due date? Can childbirth happen earlier or later than the calculated date, and why is it bad?

Even if the possible date of delivery has been calculated on the basis of ultrasound data or on the basis of the exact date of the last menstruation, it should not be completely trusted. Only 4% of all children are born on the calculated date, while the remaining 96% are born a few days or weeks earlier or later than the calculated date.
This is explained by the fact that in addition to errors that, of course, can occur when calculating the possible date of birth, the duration of a normal pregnancy can vary from 37 to 42 weeks, and children born during this period are considered born on time.

Estimated due date calculation based on gestational age

Knowing the exact gestational age, you can easily calculate the estimated due date. The duration of a normal pregnancy is, on average, 280 days (if counted from the first day of the last menstruation) or 40 weeks.

Thus, in order to find out the estimated date of birth from 40, you should calculate the current gestational age (in weeks) and measure the resulting number of weeks ahead according to the calendar.

Estimated due date based on last menstrual date

Pregnancy and estimated due date based on last menstrual date based on the assumption that with an average menstrual cycle (period between two periods) of 28 days, ovulation and conception is possible approximately 14 days after the start of the last menstruation.

This calculation is very inaccurate for the following reasons:

• Approximately 20-40% of women cannot tell the exact date of the last menstruation
• The duration of the menstrual cycle may vary from woman to woman. For example, for some women, the period between two periods can be 21 days, while for others it can be 42 days.
• Many women have irregular menstrual cycles. This means that the moment of ovulation can occur on completely different days of the menstrual cycle (closer to its beginning or closer to its end)

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Calculating the estimated due date and due date using ultrasound

Ultrasound is one of the most accurate modern methods for determining the age of pregnancy and the estimated due date.

In the first trimester, it is possible to determine the age of pregnancy by measuring the diameter of the ovum, crown-rump length (CRL), or the fetal heartbeat.

The gestational age in days is equal to: the diameter of the ovum in millimeters + 30

The gestational age in weeks is: