Pregnancy due date calculator
Enter the first day of your last period (or a conception or IVF transfer date) to estimate your due date, how far along you are and when each trimester starts.
Calculated in your browser and never stored. An estimate only — your healthcare provider’s dating (often by ultrasound) takes priority.
How the due date is estimated
This uses Naegele’s rule: the due date is 280 days (40 weeks) after the first day of your last menstrual period, adjusted if your cycle is longer or shorter than 28 days. Pregnancy weeks are counted from that date, about two weeks before conception — so at “4 weeks pregnant”, the embryo is about two weeks old.
Only about 4% of babies arrive on their due date; most are born between 37 and 42 weeks. A first-trimester ultrasound is the most accurate way to date a pregnancy, and your provider may update your due date after it.
If you have questions, talk to your doctor, midwife or nurse practitioner. In Canada you can also call your province’s health line (811 in most provinces).
Counting down? Set a shareable countdown to your due date.
Frequently asked questions
How accurate is a due date calculator?
It gives the standard clinical estimate, but natural variation means birth within two weeks either side is normal.
Why does pregnancy count from my last period?
Because the date of the last period is usually known, while the exact conception date isn’t. It adds about two weeks before conception.
What if my cycle isn’t 28 days?
Enter your average cycle length; the due date shifts by the difference from 28 days.