Pregnancy and due date calculator

From your last period or conception date: estimated due date, weeks pregnant and trimester.

How it works

The due date is worked out by adding 280 days (40 weeks) to the first day of your last period, adjusted if your cycle isn’t 28 days. If you know the conception date, 266 days are added.

Only about 4–5% of babies arrive on that exact day: anywhere between week 37 and 42 is normal. The first-trimester scan gives a more accurate date.

Due date = last period + 280 days + (cycle length − 28)

Frequently asked questions

Are weeks counted from conception?

No: they’re counted from your last period, about two weeks before conception. That’s why at “week 4” the embryo is about two weeks old.

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