Due Date Calculator
Estimate your due date from your last period, conception date, or a known due date.
How this works
Pregnancies are dated from the first day of your last menstrual period (LMP), not from conception. The full term is 280 days (40 weeks) from LMP, or about 266 days from conception. This rule (Naegele's rule) has been the clinical standard since 1812.
If your cycle is longer or shorter than 28 days, we adjust: a 32-day cycle pushes conception 4 days later, which moves the due date 4 days later too. Only about 5% of babies arrive on their predicted due date; most come within two weeks either side.
When to see a clinician
This tool is for planning, not diagnosis. Confirm your due date with your OB or midwife. An early ultrasound is the most accurate way to date a pregnancy.