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Due date calculator

The first day of your last period or the conception date in; the estimated due date, the week today and the trimester dates out.

Your numbers

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Naegele’s rule: the first day of the last period plus 280 days, moved by the difference between your cycle length and 28 days.

The pre-filled date is an example, ten weeks back from today. Enter your own.

First day of one period to the first day of the next. 28 is the standard the rule assumes.

Today, unless you want to read another date.

Result

Estimated due date

May 26, 2027

Completed weeks on that date
10
Plus days
0
Trimester on that date (1, 2 or 3)
1
Days until the due date
210 days
Second trimester starts (14 weeks)
November 25, 2026
Third trimester starts (28 weeks)
March 3, 2027

The estimated due date is May 26, 2027.

An estimate by a convention, not a prediction: few babies are born on the day. Naegele’s rule assumes ovulation 14 days after the period starts, adjusted here for your cycle length. If you have had an ultrasound, the due date from maternity care is the one that applies. Trimesters are counted from 14 and 28 completed weeks. Not medical advice.

The calculator uses Naegele’s rule: the due date is 280 days (40 weeks) after the first day of the last period, which assumes a 28-day cycle with ovulation on day 14. If your cycle is longer or shorter, the date moves by the difference. From a conception date it adds 266 days. Trimesters start at 14 and 28 completed weeks.

Example. A last period starting 1 January 2026 gives 8 October 2026; on 12 March 2026 that is 10 weeks and 0 days, in the first trimester.

It is an estimate by a convention, not a prediction. If you have had an ultrasound, the due date from maternity care is the one that applies.

Last reviewed October 20, 2026 ·How pages are reviewed

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