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Due date calculator

When is my baby due?

Work out your due date from your last period, a conception date, an IVF transfer or an ultrasound. You'll see how far along you are today, when each trimester ends, and the routine visits coming up.
days

A longer cycle means later ovulation, so a later due date. Leave at 28 if you're not sure.

Enter a date to see your due date and the weeks ahead.

Four ways to date a pregnancy

From your last period. The standard starting point, known as Naegele's rule: the first day of your last period plus 280 days. It assumes ovulation on day 14, so for a longer or shorter cycle the calculator moves the date by the difference. A period that started Nov 2, 2026 in a 31-day cycle gives a due date of Aug 12, 2027.

From conception. If you know the day, from ovulation tests or because there was only one possible date, add 266 days.

From an IVF transfer. The embryo's age is known to the day, so this is the most exact date there is: 263 days after a day-3 transfer, 261 after day 5, 260 after day 6.

From an ultrasound. Enter the scan date and the age it measured, in weeks and days. Scans in the first trimester, up to about 13 weeks, date a pregnancy most accurately. ACOG recommends using a first-trimester scan over your period dates when they differ by more than a few days.

What the due date really means

It's the 40-week point, the middle of a normal range. Babies born from 37 weeks are early term, 39 to 40 weeks full term, and 41 weeks late term. Most people go into labor somewhere in that span, and only a handful on the day itself.

If you'd like to know when you conceived, the conception date calculator works it back from the same dates.

The weeks ahead

Once you have a date, the rest of the pregnancy has a shape: a first visit around 8 to 10 weeks, optional screening from 10 weeks, the anatomy scan between 18 and 22, the glucose test between 24 and 28, the whooping cough vaccine from 27 weeks, and the group B strep test at 36 to 37. Every practice runs its own version, so treat these as a guide and follow your clinician.

CycleHelm Pro follows your due date week by week: what's developing, what's changing for you, what to do and what to ask, with a short email when each new week starts.

Questions people ask

How is a due date calculated?

From the first day of your last period, add 280 days (40 weeks). If your cycles are longer or shorter than 28 days, the date moves by the difference, because ovulation moves. From a known conception date it's 266 days; from an IVF transfer it's 266 days minus the embryo's age.

Why am I '4 weeks pregnant' when I conceived two weeks ago?

Pregnancy is counted from the first day of your last period, about two weeks before conception, because that date is the one most people know. So at conception you're already counted as about two weeks along.

Will my due date change?

It might, once. If a first-trimester ultrasound measures a different age than your dates suggest, your clinician may move the due date to match the scan. After that it usually stays put, even if later scans show a bigger or smaller baby.

How likely is it that my baby comes on the due date?

Not very: only about 4 in 100 babies do. Anywhere from 37 to 42 weeks is a normal time to give birth. The due date is the middle of that range, not a deadline.

Which method is most accurate?

IVF dates are exact. Otherwise a first-trimester ultrasound is the most accurate way to date a pregnancy, more so than the date of your last period, which depends on remembering it and on when you ovulated.

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