Pregnancy Due Date Calculator
Estimated due date from your last period, conception date, IVF transfer or a dating scan.
An estimated due date is 40 weeks from the first day of your last period. Only about one baby in twenty arrives on it — most births happen in the two weeks either side — so it is best read as the middle of a window rather than an appointment.
How this is worked out
Naegele's rule adds 280 days to the first day of the last period. Because that assumes a 28-day cycle with ovulation on day 14, the calculator adjusts by the difference between your cycle length and 28 days. Conception dating adds 266 days; IVF adds 266 days minus the embryo's age at transfer; a dating scan simply counts forward from the gestational age measured on the day.
A first-trimester ultrasound is the most accurate dating method there is, and where it differs from the period-based date by more than five to seven days, maternity services generally go with the scan.
A pregnancy is considered full term from 39 weeks 0 days to 40 weeks 6 days, early term from 37 weeks, late term at 41 weeks and post-term from 42 weeks — the thresholds your care team will be watching.
This calculator runs entirely in your browser. Nothing you enter is transmitted to us, saved on our servers, or shared with anyone.
Common questions
How accurate is a due date?
About 4% of babies arrive on the estimated date, and roughly two-thirds within a week of it. A dating scan narrows the window; irregular cycles widen it.
My cycle is not 28 days. Does it matter?
Yes. Ovulation timing drives conception, so a 35-day cycle typically shifts the due date about a week later. Enter your real average cycle length above.
How many weeks pregnant am I?
Gestational age is counted from the first day of your last period, not from conception — which is why you are considered about two weeks pregnant at the moment of conception. The result panel shows today's figure.