Pregnancy due date calculator
Estimate a due date and how many weeks along a pregnancy is, from the first day of the last period.
An estimate only. Your doctor or midwife will confirm or adjust the date, often after an early ultrasound.
How this calculator works
Naegele's rule: due date = first day of last period + 280 days (40 weeks). For cycles longer or shorter than 28 days, the date shifts by the difference.
Worked example: a last period starting 1 March with a 28-day cycle gives an estimated due date of 6 December. With a 31-day cycle it moves to 9 December.
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