Pregnancy Due Date
Estimate your likely due date and weeks of pregnancy (Naegele's rule).
Estimate: last period + 280 days. Confirm with your doctor.
Pick a date.
How it works
The estimated due date is one of the first things expectant parents want to know. This calculator works it out from the first day of your last menstrual period using Naegele’s rule, the standard method.
Naegele’s rule adds 280 days (40 weeks) to the first day of your last period. In practice that is: take that date, subtract three months and add seven days and one year. A last period starting 1 April 2025 gives a due date around 6 January 2026.
Only about one in twenty babies arrives exactly on the due date — most come within two weeks either side — so treat it as the centre of a window, not a fixed appointment. An ultrasound scan can refine the estimate.
Frequently asked questions
How accurate is the due date?
It is an estimate. Only about 5% of babies are born on the exact date; most arrive within a week or two either side. A dating scan in early pregnancy usually gives a more precise figure.
What if my cycle is not 28 days?
Naegele’s rule assumes a 28-day cycle with ovulation around day 14. If your cycle is much longer or shorter, the date can shift by a few days, and a scan is the best way to confirm.
What about an irregular cycle?
The last-period estimate is less reliable and should be confirmed by a healthcare professional.