free due date calculator
Pregnancy Due Date Calculator
Estimate your due date and current pregnancy week from the first day of your last period or a known conception date.
How the estimate works
Pregnancy is conventionally dated from the first day of the last menstrual period, about two weeks before conception in a typical cycle. Naegele’s rule adds 280 days. When conception is known, 266 days is used instead.
Cycle length, uncertain dates, IVF and early ultrasound measurements can change the estimate. Your clinical due date should come from your maternity team.
Common questions
How is a pregnancy due date calculated?
The common period-based estimate adds 280 days to the first day of the last menstrual period. If conception is known, the estimate adds 266 days.
Can the due date change after an ultrasound?
Yes. A first-trimester dating scan may be more reliable than a period-based estimate, especially when cycles are irregular or the last period date is uncertain.
Do most babies arrive on the due date?
No. A due date is an estimate, not an appointment. Your maternity team will explain the normal birth window and any plan for monitoring.