Due date calculator
The dates stay in this tab. Nothing is uploaded.
Pregnancy
Naegele's rule: due date = last period + 280 days, shifted by cycle length − 28.
An estimate, not medical advice. An early ultrasound gives the most reliable date.
How to use this tool
Estimate the due date, the week of pregnancy and the trimester dates. Nothing is uploaded.
Open Due date calculator
Last period is selected with a sample date 10 weeks ago and a 28-day cycle. The due date and today's week sit on the right.
Enter your date and cycle
Type the first day of the last period. If your cycle is not 28 days, change the length; a 32-day cycle moves the due date 4 days later.
Or start from conception or a known due date
Switch I know my to Conception date or Due date and enter it. Weeks, trimesters and the other dates follow. Copy puts them on the clipboard.
FAQ
How is the due date calculated?
With Naegele's rule: 280 days (40 weeks) after the first day of the last period for a 28-day cycle. A longer or shorter cycle shifts the date by the difference, so a 32-day cycle adds 4 days.
Is anything uploaded?
No. The dates are computed in this tab and nothing is stored.
What if I know the conception date instead?
Pick Conception date. The due date is 266 days after it. If you already have a due date from a scan, pick Due date to see the weeks and trimesters.
How accurate is it?
Only about 4% of babies arrive on the due date; most come within two weeks either side. An early ultrasound gives the most reliable date and overrides this estimate.
When do the trimesters start?
The second trimester starts at 13 weeks + 0 days and the third at 27 weeks + 0 days, counted from the last period. Different books use slightly different cut-offs.