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Pregnancy Due Date Calculator

Estimate your due date from your last period, conception date, or IVF transfer. The due date calculator also shows how many weeks pregnant you are today and the key dates ahead.

Runs in your browser. Your data is not uploaded.
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Estimated due date
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For general information. Not medical advice.

How to use the Pregnancy Due Date Calculator

  1. Choose what to Calculate from: your last period, conception date, or an IVF transfer.
  2. Enter the Date. For the last-period method, set your usual Cycle length if it is not 28 days.
  3. Press Calculate. The due date appears first, then today's week of pregnancy, trimester, and key dates.

How it works

last period:   due = LMP + 280 days + (cycle length − 28)
conception:    due = conception + 266 days
IVF day 3:     due = transfer + 263 days
IVF day 5:     due = transfer + 261 days
weeks today = (today − (due − 280 days)) ÷ 7

This is Naegele's rule: 280 days from the first day of the last period. The IVF offsets are the ones in ACOG's guidance on estimating the due date. Key dates count from the equivalent last-period date: the first trimester ends at 13 weeks 6 days, the anatomy scan is around 20 weeks, and full term starts at 39 weeks.

Examples

  • Last period on January 1, 2026 with a 28-day cycle: due Thursday, October 8, 2026.
  • The same date with a 32-day cycle moves the due date 4 days later, to October 12, 2026.

How reliable is a due date?

A due date is the middle of a window, not an appointment, and few babies arrive on the day itself. An ultrasound in the first trimester, up to 13 weeks 6 days, is the most accurate way to date a pregnancy. ACOG advises changing the due date to the scan date when the two differ by more than a set number of days, and that number depends on how far along the scan was done.

Limitations

  • Cycle lengths from 21 to 45 days are supported.
  • The date must be today or in the past.
  • This is general information, not medical advice. Your midwife or doctor will confirm your dates.

Sources

Frequently asked questions

How is my due date calculated?

By Naegele's rule: 280 days (40 weeks) after the first day of your last period, adjusted for cycles longer or shorter than 28 days.

Why are pregnancy weeks counted from my last period?

Because the date of the last period is usually known, while ovulation is not. Conception typically happens about two weeks later.

Can I use my IVF transfer date?

Yes. Choose day 3 or day 5 embryo transfer; the calculator adds 263 or 261 days.

Is my information stored?

No. The calculation happens in your browser and the dates you enter are not sent anywhere.

Often used together with Pregnancy Due Date Calculator.