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Pregnancy Due Date Calculator

Estimate your baby's due date from your last period, conception date, IVF transfer or a dating scan, with how far along you are and key pregnancy milestones.

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days
Leave empty for 28 days.
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Enter a valid date.
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weeks
Enter a number, for example 1250 or 19.99.
days
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How to use the due date calculator

  • Last period: enter the first day of your last menstrual period, and your usual cycle length if it isn't 28 days.
  • Conception date: if you know when you conceived.
  • IVF transfer: enter the transfer date and whether it was a day-3 or day-5 embryo.
  • Dating scan: enter the scan date and the pregnancy age the scan gave you. If an early scan differs from your period date by more than a set amount (for example, more than 5 days before 9 weeks, or more than 7 days from 9 weeks to 13 weeks 6 days), doctors usually go by the scan.

How the due date is worked out

From last period (Naegele's rule): first day + 280 days (40 weeks), adjusted by (cycle length − 28) days
From conception: + 266 days  ·  IVF day-5 transfer: + 261 days  ·  IVF day-3 transfer: + 263 days
From a scan: scan date + (280 days − the pregnancy age at the scan)

Pregnancy is counted from the first day of the last period, about two weeks before conception. With a longer or shorter cycle than 28 days, ovulation is later or earlier, so the weeks are counted from the adjusted date. That's why a pregnancy is "40 weeks" long, though the baby has been growing for about 38.

Worked example

Last period started on 1 June 2026 with a 28-day cycle: 1 June + 280 days = 8 March 2027. Conception was probably around 15 June 2026.

With a 32-day cycle, the due date moves 4 days later, to 12 March 2027.

Trimesters

The first trimester runs to the end of week 13, the second from week 14 to week 27, and the third from week 28 until birth. A pregnancy is full term from 37 weeks.

Count days between any two dates with the date calculator.

Frequently asked questions

How accurate is a due date?

It's an estimate. Only about 1 in 25 babies is born on the due date itself; most arrive between 37 and 42 weeks.

My scan gave a different date. Which is right?

An early ultrasound is usually more accurate than dates from your period, especially if your cycle is irregular. Follow the date your midwife or doctor gives you.

Sources

Formulas checked 29 October 2026. How we test our calculators. This calculator gives general estimates for adults and is not medical advice. Talk to a doctor or dietitian about your own health.