Naegele’s rule
Most calculators add 280 days (40 weeks) to the first day of your last period. This assumes a 28-day cycle with ovulation around day 14.
Free pregnancy tool100% free • No signup required
When is my baby due?
Calculate your estimated due date and see important pregnancy dates.
Related tools
See all tools →Good to know
How due dates are estimated
Longer or shorter cycles
If your cycle is usually longer or shorter than 28 days, ovulation tends to shift too. We adjust the estimate by the difference in days.
Dating scans
An early ultrasound can measure your baby and may refine the date. If your provider gives you a different due date, use theirs.
FAQ
Questions parents ask
How accurate is a due date?
It’s an estimate. Many babies arrive in the two weeks either side of the date, and only a small share are born on the day itself.
Why is pregnancy counted from my last period?
Conception is hard to pinpoint, while the first day of a period is easier to remember. So pregnancy weeks are counted from that day — about two weeks before conception.
I know my conception date. Can I use that?
Yes. Switch to the Conception date tab. We add 266 days (38 weeks) to estimate the due date.