Due Date Calculator

Use our Due Date Calculator to estimate when your baby may be born, calculate how many weeks pregnant you are, find your estimated conception date, and view important pregnancy milestones. You can calculate your pregnancy due date from the first day of your last menstrual period, a known conception date, an IVF embryo transfer, ultrasound dating, or a due date already provided by your maternity-care professional.

A pregnancy due date is an estimate rather than a prediction of the exact day a baby will be born. This calculator is designed for planning and general information. If your doctor, midwife, fertility clinic or other maternity-care professional has established an estimated due date, use that clinically established date for medical decisions.

How to Use the Due Date Calculator

Start by choosing the calculation method that best matches the pregnancy information you know. The calculator includes five different methods because not every pregnancy is dated from the same information.

Last Period

Choose Last Period if you know the first day of your last menstrual period. Enter that date and your average menstrual cycle length. A 28-day cycle is used as the standard assumption, but the calculator can adjust the estimate for shorter or longer cycles.

Conception Date

Choose Conception Date if you have a reasonably reliable estimate of when conception occurred. The calculator adds approximately 266 days to estimate the date at which the pregnancy reaches 40 weeks of gestational age.

IVF Transfer

Choose IVF Transfer for a pregnancy resulting from in vitro fertilization. Enter the embryo transfer date and choose whether the embryo was transferred on day 3 or day 5.

Known Due Date

Choose Known Due Date if your doctor, midwife, fertility clinic or other maternity-care professional has already established your estimated due date. This mode works backward from the EDD to calculate your current gestational age, estimated conception date and pregnancy timeline.

Ultrasound

Choose Ultrasound if an ultrasound report gives a gestational age for the date on which the scan was performed. Enter the scan date and the reported age in complete weeks and additional days.

After pressing Calculate Due Date, the calculator displays your estimated due date, current pregnancy week, trimester, estimated conception date, days remaining until your due date and a personalized pregnancy timeline.

What Is a Pregnancy Due Date?

A pregnancy due date is an estimate of when a pregnancy reaches 40 weeks of gestational age. It is commonly called the estimated due date or EDD.

The date provides a useful reference point for prenatal care. Health-care professionals use gestational age to schedule and interpret certain tests, follow fetal growth and understand where a pregnancy is on its expected timeline.

The word estimated is important. A due date is not a reservation for a specific delivery day. Pregnancy length varies naturally, and only a minority of births occur on the exact calculated EDD.

A pregnancy can therefore be progressing normally even if labor does not begin on the estimated due date. Your maternity-care professional considers the complete clinical picture rather than one calendar date alone.

How Is a Due Date Calculated?

The traditional pregnancy dating system begins with the first day of the last menstrual period rather than the date of conception.

A standard pregnancy is dated as approximately 280 days, or 40 weeks, from the first day of the last menstrual period.

This can initially seem strange because conception normally happens after the menstrual period begins. Pregnancy dating includes approximately the first two weeks before conception in a typical cycle because the exact day fertilization occurred is often unknown.

That standard provides a consistent way to measure gestational age across pregnancy.

Due Date Calculator From Last Period

The last menstrual period method is one of the most widely used starting points for calculating an estimated due date.

Enter the first day of your last menstrual period. Do not enter the day the period ended.

With a 28-day menstrual cycle, the calculator adds 280 days to that first day. This produces the traditional 40-week EDD.

The calculation assumes that ovulation occurs around the middle of a typical cycle. Real menstrual cycles and ovulation timing vary, which is one reason an LMP calculation is an estimate rather than an exact measurement.

If you want to compare the LMP date with another calendar date, our Date Calculator Between Two Dates can calculate the exact number of days or weeks separating them.

How Cycle Length Affects Your Due Date

The standard 280-day due-date formula assumes a 28-day menstrual cycle. Not everyone has a 28-day cycle.

If your average cycle is longer, ovulation may also occur later than the standard calculation assumes. If your cycle is shorter, ovulation may occur earlier.

The LMP mode adjusts the due date by the difference between your cycle length and 28 days.

30-Day Cycle Example

A 30-day menstrual cycle is two days longer than the standard 28-day cycle. The calculator therefore adds two additional days to the conventional LMP due-date estimate.

26-Day Cycle Example

A 26-day cycle is two days shorter than 28 days. The calculator subtracts two days from the standard estimate.

This adjustment is most useful when cycles are reasonably regular. If cycle length varies significantly from month to month, a single average cycle length may not accurately identify ovulation timing.

Due Date Calculator From Conception Date

When the conception date is known with reasonable confidence, the estimated due date can be calculated by adding approximately 266 days, or 38 weeks.

The difference between 266 days from conception and 280 days from the last menstrual period reflects the approximately two weeks included before conception in traditional gestational dating.

Knowing the date of intercourse does not always mean the exact date of conception is known. Fertilization can occur after intercourse because sperm can remain viable for several days and ovulation timing can vary.

For that reason, conception dating is still generally an estimate unless assisted reproduction provides more precise timing information.

IVF Due Date Calculator

Pregnancy dating after IVF can use the age of the embryo and the date on which the embryo was transferred. This avoids relying on an assumed ovulation date.

The calculation is different for a day-3 embryo and a day-5 embryo because the embryos are already different ages at the time of transfer.

Day-5 Embryo Transfer

For a day-5 embryo or blastocyst transfer, the calculator adds 261 days to the transfer date.

Day-3 Embryo Transfer

For a day-3 embryo transfer, the calculator adds 263 days.

If your fertility clinic has already assigned an official estimated due date, use the clinic’s date rather than changing it based on an online calculation.

Due Date Calculator From Ultrasound

Ultrasound can be used to establish or confirm gestational age. The usefulness of ultrasound for pregnancy dating depends partly on how early the scan is performed.

First-trimester ultrasound is generally the most accurate ultrasound method for establishing or confirming gestational age. As pregnancy progresses, normal differences in fetal size become larger, which makes later ultrasound measurements less precise for assigning a pregnancy date.

The ultrasound mode on this calculator does not attempt to interpret fetal measurements such as crown-rump length, head circumference or femur length. Instead, it uses the gestational age that has already been reported on the ultrasound.

For example, suppose an ultrasound was performed on September 1 and the report states a gestational age of 8 weeks 4 days. Enter September 1, 8 weeks and 4 days. The calculator determines how many days remain until 40 weeks and estimates the corresponding EDD.

An online calculator should not be used to decide whether your clinician should change an established due date. Pregnancy redating requires interpretation of the timing of the ultrasound, menstrual history and other clinical information.

How Many Weeks Pregnant Am I?

Pregnancy is usually described in completed weeks and additional days. A gestational age of 10 weeks 4 days means ten complete weeks have elapsed and the pregnancy is four days into the following week.

The calculator works backward from the estimated due date. The EDD represents 280 days of gestational age.

If the due date is exactly 210 days away, 70 days of the standard pregnancy timeline have elapsed. Seventy days equals 10 weeks.

If the EDD has already been established clinically, choose Known Due Date. This can be particularly useful when your due date was changed after an early ultrasound or established from fertility-treatment records.

Pregnancy weeks are counted from the obstetric dating reference point rather than from the moment conception occurred. That is why the first approximately two weeks of the conventional 40-week pregnancy timeline normally occur before conception.

Pregnancy Trimesters

Pregnancy is commonly divided into three trimesters. This calculator uses gestational age to identify the current trimester.

• First trimester: through 13 weeks 6 days.
• Second trimester: 14 weeks 0 days through 27 weeks 6 days.
• Third trimester: begins at 28 weeks.

The trimester result changes automatically as the calculated gestational age passes these boundaries.

Pregnancy Timeline

Once the estimated due date has been calculated, the tool works backward and forward to create calendar dates for several points in the pregnancy timeline.

8 Weeks Pregnant

Eight weeks is early in the first trimester. The calculator displays the calendar date corresponding to 8 weeks based on the selected EDD.

12 Weeks Pregnant

Twelve weeks is near the end of the first trimester. Early pregnancy scans and screening may occur around this general period depending on the health-care system and individual pregnancy.

14 Weeks Pregnant

At 14 weeks, the pregnancy has entered the second trimester using the trimester definitions applied by this calculator.

20 Weeks Pregnant

Twenty weeks is halfway through the conventional 40-week pregnancy timeline. It represents 140 days of gestational age.

If you want to calculate percentages of another time period, use our Percentage Calculator.

28 Weeks Pregnant

Twenty-eight weeks marks the beginning of the third trimester in this calculator.

37 Weeks Pregnant

At 37 weeks, the pregnancy has entered the later part of its expected timeline. The estimated due date is still three weeks away.

40 Weeks Pregnant

Forty weeks corresponds to the estimated due date. It is the central reference point used by pregnancy dating rather than a guarantee that labor will start that day.

42 Weeks Pregnant

The calculator also displays the calendar date corresponding to 42 weeks. Pregnancy management near and after the estimated due date should be discussed with your maternity-care professional.

Estimated Conception Date

The calculator estimates conception approximately 266 days before the EDD.

This is useful for understanding the pregnancy timeline, but in a naturally conceived pregnancy it should not be interpreted as proof that fertilization occurred on that exact calendar date.

Ovulation can vary, intercourse may occur several days before fertilization and the exact biological timing may not be known.

IVF is different because embryo age and transfer timing are documented, allowing pregnancy dating to use more specific information.

What Is Gestational Age?

Gestational age describes how far a pregnancy has progressed using the standard obstetric dating system.

It is usually measured from the first day of the last menstrual period or from an equivalent dating point established through ultrasound or assisted reproduction.

Gestational age is therefore normally about two weeks greater than conceptional age in a typical 28-day menstrual cycle.

A pregnancy described as 10 weeks gestational age may therefore be approximately eight weeks from conception.

Why Is Pregnancy Counted From the Last Period?

In many naturally conceived pregnancies, the exact moment of fertilization is impossible to identify. The first day of the last menstrual period is often easier to identify and provides a consistent reference point.

The system therefore begins counting pregnancy before conception is expected to occur.

This is why someone described as four weeks pregnant may have conceived only about two weeks earlier.

Why Is Pregnancy 40 Weeks but Often Called Nine Months?

Forty weeks equals 280 days, but calendar months are not all four weeks long.

Four weeks equals only 28 days. Most calendar months contain 30 or 31 days, while February contains 28 days or 29 in a leap year.

Because weeks are a consistent seven days long, pregnancy care usually describes gestational age in weeks and days instead of relying on calendar months.

How Many Days Until My Due Date?

The results calculate the number of calendar days between today and your EDD.

If your due date is 100 days away, the calculator displays 100 days. If today is the estimated due date, it displays that the due date is today.

If the date has passed, the calculator shows how many days have elapsed since the EDD rather than displaying a confusing negative number.

For general date countdowns that are not pregnancy related, use our Date Calculator Between Two Dates.

Pregnancy Progress Percentage

The progress bar compares your current estimated gestational age with the conventional 280-day pregnancy timeline.

At 10 weeks, approximately one quarter of the 40-week timeline has elapsed. At 20 weeks, approximately 50% has elapsed. At 30 weeks, approximately 75% has elapsed.

The percentage is simply a way of visualizing elapsed gestational time. It does not measure fetal health, fetal growth, the likelihood of labor or the progress of an individual pregnancy in a medical sense.

How Accurate Is a Due Date Calculator?

The reliability of a due-date estimate depends on the information used to create it.

Last Menstrual Period

LMP dating can work well when the date is remembered accurately and menstrual cycles are reasonably regular. It can be less reliable when periods are irregular, the LMP date is uncertain or ovulation occurred much earlier or later than expected.

Conception Date

A known conception date can provide useful information, but the precise day of conception can be difficult to identify in a naturally conceived pregnancy.

IVF Dating

IVF provides documented embryo age and transfer timing, allowing the estimated due date to be assigned using the assisted-reproduction timeline.

Early Ultrasound

An early first-trimester ultrasound can provide accurate pregnancy dating information. Ultrasound dating becomes less precise later in pregnancy because normal differences in fetal size increase over time.

If your calculator result differs from an EDD already established by your maternity-care professional, do not replace the clinical EDD with the calculator result.

Why Your Due Date May Change After an Early Ultrasound

An LMP estimate assumes a typical menstrual cycle and approximate timing of ovulation. If either assumption is wrong, an early ultrasound may indicate a different gestational age.

The difference can occur because the remembered LMP was incorrect, menstrual cycles were irregular, ovulation happened on a different day than expected or bleeding was mistaken for a menstrual period.

When a clinically appropriate EDD has been established, it generally should not move every time another ultrasound produces a slightly different measurement. Normal variation in fetal size becomes increasingly important later in pregnancy.

What if I Do Not Know My Last Period?

If you cannot remember the first day of your last menstrual period, avoid inventing a date just to make the calculator produce a result.

Instead, use another method if appropriate. You may know the conception date, have IVF records, have an ultrasound report with gestational age or already have an EDD established by your maternity-care professional.

If pregnancy dates are uncertain, discuss them with your doctor or midwife because accurate dating can affect prenatal care.

What if My Periods Are Irregular?

Irregular periods can make an LMP due-date estimate less reliable because the timing of ovulation may vary from one cycle to another.

The cycle-length adjustment is most helpful when your cycles are regularly shorter or longer than 28 days. It cannot fully account for unpredictable ovulation.

When menstrual dating is uncertain, early ultrasound may provide better information for establishing gestational age.

Due Date Calculator vs. Pregnancy Calculator

The terms due date calculator and pregnancy calculator are often used to describe similar tools.

A simple due date calculator may provide only the estimated date of delivery. A more detailed pregnancy calculator can also show current gestational age, trimester, conception estimate and pregnancy milestones.

This calculator combines both functions. The due date is the primary result, while the additional results help explain where the pregnancy falls within the 40-week timeline.

Due Date Calculator vs. Conception Calculator

A due-date calculator normally starts with an earlier pregnancy date and calculates forward to the EDD.

A conception calculator can work backward from a due date by subtracting approximately 266 days.

This calculator does both. If you enter a conception date, it estimates the due date. If you enter a known due date, it estimates the conception date.

Due Date Calculator vs. Date Calculator

A general date calculator measures time between arbitrary calendar dates. A pregnancy due date calculator adds pregnancy-specific rules such as gestational age, trimester boundaries, IVF embryo age and a 40-week timeline.

If you simply need to know how many days separate two dates, the Date Calculator Between Two Dates is the better tool.

If you need to calculate elapsed clock time instead of pregnancy dates, our Time Calculator handles hours, minutes and time intervals.

Can My Baby Be Born Before the Due Date?

Yes. The estimated due date is not the earliest date on which birth can occur, and it is not a prediction that pregnancy will continue until exactly 40 weeks.

Pregnancy duration varies naturally. How a birth is classified medically depends on gestational age and other clinical factors.

If you have symptoms of labor, bleeding, fluid leakage, pain, reduced fetal movement or another pregnancy concern, contact your maternity-care provider rather than relying on an online due-date calculation.

Can Pregnancy Go Past the Due Date?

Yes. It is possible for pregnancy to continue after the estimated due date.

The EDD is a reference date at 40 weeks, not a deadline. Your maternity-care professional may recommend additional monitoring or discuss management options as pregnancy continues beyond the estimated date.

The calculator displays the 42-week calendar date for reference, but it does not provide recommendations about induction, monitoring or delivery timing.

How Far Along Am I?

When someone asks “how far along am I?”, they are usually asking for gestational age.

The result is normally written in weeks and days. For example, 16 weeks 5 days means sixteen complete weeks have elapsed and the pregnancy is five days into the seventeenth week.

You can calculate this using the LMP method, or you can enter a known EDD if your pregnancy has already been dated clinically.

When Does the Second Trimester Start?

The second trimester begins at 14 weeks 0 days using the trimester definitions applied by this calculator.

The second trimester then continues through 27 weeks 6 days.

When Does the Third Trimester Start?

The third trimester begins at 28 weeks 0 days.

The calculator automatically labels the pregnancy as third trimester when the calculated gestational age reaches that point.

How Many Months Pregnant Am I?

Pregnancy is more accurately tracked in weeks than months because calendar months have different lengths.

Four weeks equals 28 days, which is shorter than most calendar months. For that reason, statements such as “five months pregnant” are useful conversationally but are less precise than a gestational age such as 22 weeks 3 days.

The calculator therefore reports pregnancy age in weeks and days instead of trying to force every stage into an exact number of months.

How Long Until My Baby Is Due?

The results show the number of days between today and the estimated due date.

You can divide the number by seven to think of the remaining time in weeks, although the gestational-age result already provides the more medically useful measurement of how far the pregnancy has progressed.

Remember that “days until due date” means days until the 40-week EDD. It is not a countdown that predicts exactly when labor will begin.

Common Due Date Calculation Mistakes

• Using the last day of the menstrual period: LMP dating uses the first day of the last menstrual period.
• Assuming every cycle is 28 days: A consistently shorter or longer cycle can shift the basic LMP estimate.
• Adding nine calendar months instead of 280 days: Calendar months have different lengths.
• Assuming intercourse date equals conception date: Fertilization may occur days after intercourse.
• Ignoring embryo age in IVF: A day-3 and day-5 embryo transfer use different due-date calculations.
• Treating a due date as an exact delivery date: The EDD is an estimate.
• Redating a pregnancy from every later ultrasound: Pregnancy dating decisions should be made clinically rather than by repeatedly changing the EDD yourself.
• Using a calculator instead of prenatal care: An online calculator cannot evaluate maternal or fetal health.

Due Date Calculator Frequently Asked Questions

Final Thoughts

A useful Due Date Calculator should account for the fact that pregnancy dating can begin with different information. Someone may know the first day of their last period, have a reasonably clear conception date, have precise IVF records, have an ultrasound-reported gestational age or already have a clinically established EDD.

For a typical 28-day cycle, the traditional calculation uses 280 days from the first day of the last menstrual period. A conception-based estimate uses approximately 266 days from conception. IVF pregnancy dating uses the embryo’s age and transfer date, which is why day-3 and day-5 transfers have different formulas.

The calculator then uses the EDD to estimate your current pregnancy week, trimester, conception date, pregnancy progress and calendar dates for major points throughout the 40-week timeline.

Use the result as a planning estimate. If a maternity-care professional has already established your due date from your menstrual history, early ultrasound, IVF records or other clinical information, that clinically established EDD should take precedence over an online calculator.