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Pregnancy Due Date Calculator

Find your estimated due date from the first day of your last menstrual period (LMP), plus the key dates for each trimester.

Pregnancy Due Date Calculator

Your estimated due date, based on your last period.

First day of your last period (LMP)

Your estimated due date

–40 weeks

Approximate conception–

End of 1st trimester–

End of 2nd trimester–

40 weeks from the first day of your last period.

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How to use this calculator

Enter the first day of your last menstrual period, then press Calculate. You will see your estimated due date (40 weeks from that date), the approximate conception date and when each trimester ends.

Formula

Due date = first day of last period + 280 days (40 weeks)

This is Naegele’s rule, the standard method used by doctors. Conception is assumed to be about 14 days after the last period.

Frequently asked questions

How accurate is the due date?

It is an estimate. Most babies arrive within two weeks either side of the due date. An early ultrasound gives a more accurate date.

What if my cycles are irregular?

Naegele’s rule assumes a 28-day cycle. If your cycles are much longer or shorter, the estimate is less reliable — ask your doctor for a dating scan.

What are the trimesters?

The first trimester runs from week 1 to week 13, the second from week 14 to week 27, and the third from week 28 until birth.

Disclaimer: This calculator provides general information only and is not medical advice. The due date is an estimate — only about 5% of babies arrive on their due date. Confirm your dates with your doctor or midwife, especially with an ultrasound.