Due Date Calculator
Estimate your baby's due date from your last period, conception date or IVF embryo transfer.
About the Due Date Calculator
Pregnancy is dated from the first day of the last menstrual period (LMP): the due date is LMP + 280 days (Naegele's rule), adjusted if your cycles are longer or shorter than 28 days. From conception add 266 days; for IVF, add 261 days to a day-5 transfer or 263 to a day-3 transfer. ACOG recommends that a first-trimester ultrasound, if it differs enough, sets the final due date.
The formula
Due date = LMP + 280 days + (cycle length − 28)
Worked example
Example: Estimated due date = Sun, 11 October 2026
- Inputs: Based on: First day of last period; Date: 1 January 2026; Average cycle length: 31 days.
- Formula: Due date = LMP + 280 days + (cycle length − 28)
- Result: Estimated due date = Sun, 11 October 2026
Questions people ask
How accurate is the due date?
It's an estimate; full term is 39 weeks 0 days to 40 weeks 6 days.
Does a cycle longer or shorter than 28 days change my due date?
Yes. Ovulation moves with cycle length, so each extra day of cycle pushes the due date a day later, and each day shorter brings it a day earlier.