Pregnancy due date calculator
Enter the first day of your last period (and your cycle length if it is not 28 days) to get an estimated due date and pregnancy week.
Estimate using Naegele's rule (280 days from the last period). An ultrasound and your doctor give the most accurate date.
About this tool
The calculator uses Naegele's rule: due date = first day of last period + 280 days (40 weeks), adjusted if your cycle is longer or shorter than 28 days.
Only a small share of babies arrive on the exact estimated date. An early ultrasound and your midwife or doctor provide the most reliable dating. Nothing you enter is stored or sent.
FAQ
How is the due date calculated?
By adding 280 days to the first day of the last menstrual period, with an adjustment for cycle length.
How accurate is it?
It is an estimate; most babies are born within two weeks before or after it.