Due date calculator

Last period + 280 daysIVF transfers tooDays to go

Your estimated due date is Friday, May 28, 2027.

210 days to go

Today you are 10 weeks pregnant, in the first trimester. This is an estimate: only about 1 in 20 babies arrive on their due date. If your doctor or midwife has given you a date from a scan, go by theirs.

Milestone	Date	When
Second trimester starts (14 weeks)	Friday, November 27, 2026	in 28 days
Third trimester starts (28 weeks)	Friday, March 5, 2027	in 126 days
37 weeks: no longer preterm	Friday, May 7, 2027	in 189 days
Due date (40 weeks)	Friday, May 28, 2027	in 210 days
42 weeks	Friday, June 11, 2027	in 224 days

210 days to go, on your home screen.

Countdown keeps your due date on your iPhone’s home and lock screens and takes a day off every morning. You can send the same countdown to family.

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How your due date is worked out

Pregnancy is counted from the first day of your last period, not from conception, and lasts 40 weeks, or 280 days, on average. Conception usually happens about two weeks in, so those first two weeks are part of the count. A cycle longer or shorter than 28 days moves the date by the difference. After IVF the start is the transfer: 261 days to the due date for a day-5 embryo, 263 for a day-3 embryo.

Weeks are given as completed weeks and days: “30 weeks 4 days”, sometimes written 30+4. Your doctor may also say you’re in your 31st week; that means the same thing.

It’s an estimate

Only about 1 in 20 babies arrive on the due date itself. Most are born between 37 weeks, when a baby is no longer preterm, and 42 weeks. An ultrasound in the first trimester is the most accurate way to date a pregnancy, and your doctor or midwife may adjust your due date after it. If they have, go by their date; choose “A due date from my doctor or scan” above to count from it.

This calculator is for information only and isn’t medical advice. If you’re unsure of your dates, or something doesn’t feel right, talk to your doctor or midwife.

Trimesters and the weeks that matter

First trimester: up to 13 weeks 6 days.
Second trimester: 14 weeks 0 days to 27 weeks 6 days.
Third trimester: from 28 weeks 0 days.
37 weeks: from here a birth isn’t preterm.
39 to 40 weeks: full term.
42 weeks: by now nearly all labors have started on their own.

These are ACOG’s boundaries, used in the US. The NHS in the UK counts the second trimester from week 13, and offers the dating scan between 11 weeks 2 days and 14 weeks 1 day, and the anomaly scan between 18 weeks and 20 weeks 6 days.

Sources

Last checked 1 October 2026

Questions people ask

How is a due date calculated?

Add 280 days, or 40 weeks, to the first day of your last period. If your cycle is longer or shorter than 28 days, move the date by the difference: a 32-day cycle puts it 4 days later. The NHS calculator and ACOG use the same count.

How many weeks pregnant am I?

Count the days since the first day of your last period and divide by 7. If your last period started on March 1, 2026, then on October 1, 2026 you are 30 weeks and 4 days pregnant, which is also called being in your 31st week.

How do you calculate a due date after IVF?

Add 261 days to the transfer date for a day-5 (blastocyst) embryo, or 263 days for a day-3 embryo. A scan doesn’t change an IVF due date; go by the date your clinic gives you.

How accurate is a due date?

It’s an estimate. Only about 1 in 20 babies arrive on their due date, and most are born between 37 and 42 weeks. An early ultrasound, before 14 weeks, is the most accurate way to date a pregnancy, so once you’ve had one, the date from it is the one to use.

When does the second and third trimester start?

Going by ACOG, the first trimester runs to 13 weeks 6 days, the second from 14 weeks 0 days to 27 weeks 6 days, and the third from 28 weeks 0 days. In the UK the NHS starts the second trimester at week 13.

Counting down to something else? Make your own countdown, or see the days between two dates.