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Due date calculator

Find your due date and how many weeks pregnant you are, from your last period, conception or IVF transfer.

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Usually 28 days. A longer or shorter cycle moves the due date later or earlier.

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How to use

  1. Choose what to calculate from:
    • Last period: the first day of your last menstrual period. This is what most people use.
    • Conception: if you tracked ovulation and know the date.
    • IVF transfer: the date of your embryo transfer, plus whether it was a day-3 or day-5 embryo.
    • Known due date: if your doctor already gave you a due date, enter it to see how far along you are.
  2. Pick the date. For the last-period method, change the cycle length if yours isn’t 28 days.
  3. You get your due date, how many weeks and days pregnant you are today, your trimester, the days left, and the date of your next prenatal visit. Below that is a typical visit schedule with a date for each visit.

How it is calculated

  • From your last period: due date = first day of last period + 280 days + (cycle length − 28) days
  • From conception: due date = conception date + 266 days
  • From an IVF transfer: due date = transfer date + 261 days (day-5 embryo) or + 263 days (day-3 embryo)
  • Weeks pregnant = today − (due date − 280 days), shown as weeks and days

For example, if your last period started on March 2, 2026 and your cycle is 28 days, your due date is December 7, 2026. With a 32-day cycle, ovulation is likely 4 days later, so the due date moves to December 11, 2026.

The IVF rule works backward from conception. A day-5 embryo was fertilized 5 days before transfer, so the due date is 266 − 5 = 261 days after the transfer. A day-5 transfer on June 12, 2026 gives a due date of February 28, 2027; a day-3 transfer on the same day gives March 2, 2027.

Typical prenatal visit schedule

A common schedule is a visit every 4 weeks until 28 weeks, every 2 weeks until 36 weeks, and then every week until birth. Your schedule may differ, especially if you have a higher-risk pregnancy. Key tests along the way:

  • First visit (around 8 weeks): dating ultrasound, blood type and Rh factor, blood count, urine test, and screening for infections such as hepatitis B, syphilis and HIV
  • 10–13 weeks: optional genetic screening, either cell-free DNA (from 10 weeks) or first-trimester screening
  • 15–22 weeks: optional quad screen
  • 18–22 weeks: anatomy ultrasound
  • 24–28 weeks: glucose screening for gestational diabetes
  • 36–37 weeks: group B strep test

Reminder

This calculator estimates dates. It does not replace prenatal care. If you have questions or anything feels wrong during your pregnancy, talk to your doctor or midwife.

FAQ

How is a due date calculated?

The standard method, Naegele's rule, adds 280 days (40 weeks) to the first day of your last menstrual period. If your cycle is longer or shorter than 28 days, the date moves later or earlier by the difference. From a known conception date, the due date is 266 days (38 weeks) later.

How is the due date calculated after IVF?

It uses the transfer date and the embryo's age, not your last period. The due date is 261 days after transferring a day-5 embryo (blastocyst), or 263 days after a day-3 embryo. This is the method recommended by the American College of Obstetricians and Gynecologists (ACOG).

Why does pregnancy count from my last period, not conception?

Most people know the date of their last period but not the day they conceived, so weeks of pregnancy are counted from the first day of the last period. That means you are already about 2 weeks pregnant on the day you conceive.

What are the trimesters?

ACOG defines the first trimester as up to 13 weeks and 6 days, the second trimester as 14 weeks 0 days to 27 weeks 6 days, and the third trimester as 28 weeks 0 days onward.

How likely is my baby to arrive on the due date?

Only about 1 in 20 babies is born on the due date. A birth from 39 weeks 0 days through 40 weeks 6 days is "full term", and 37 weeks 0 days through 38 weeks 6 days is "early term".

My ultrasound gave a different due date. Which one is right?

Go with the date your doctor or midwife gives you. When the last period is uncertain or doesn't match an early ultrasound, they often adjust the due date based on the baby's measurements. Choose "Known due date" and enter it to see your weeks and visit dates.

Sources

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