Estimate your due date from the first day of your last menstrual period. The calculator also shows an estimated conception date and how many weeks pregnant you are today.
How the due date calculator works
It uses Naegele’s rule: due date = first day of last period + 280 days (40 weeks). If your cycle is not 28 days, the date shifts by the difference. Conception is estimated at cycle length minus 14 days after your last period.
Example
If your last period began on 1 January 2026, the estimated due date is 8 October 2026 and conception is estimated around 15 January 2026.
Frequently asked questions
How accurate is a due date?
It is an estimate. Only about 4 to 5 percent of babies are born on their due date, and most arrive within two weeks either side.
What if my cycle is irregular?
The estimate may be off. An early ultrasound gives a more reliable date, so speak to your doctor or midwife.
Is this medical advice?
No. It is for general information only. Always confirm your due date with a healthcare professional.
Please note: results are estimates for general information only and are not medical advice. Read our full disclaimer.