Estimate your due date from last period, conception date or ultrasound.
Due date is estimated with Naegele's rule: 280 days (40 weeks) from the first day of your last menstrual period, adjusted if your cycle differs from 28 days.
Naegele's rule
EDD = LMP + 280 days + (cycle length − 28 days)
This is an estimate only and not a substitute for professional prenatal care. Always confirm your due date with your doctor or midwife.
Only about 4% of babies arrive exactly on their due date. It's a best estimate — most births occur within two weeks either side.
This calculator shifts the due date by the difference between your average cycle length and the standard 28 days, which improves the estimate for longer or shorter cycles.