About pregnancy due date calculator
A due date estimates when a baby will be born. Doctors count pregnancy from the first day of the last period, and a full-term pregnancy is about 40 weeks.
How it is calculated
Naegele's rule adds 280 days (40 weeks) to the first day of the last menstrual period. If you know the conception date, the due date is about 266 days later.
An estimate only
Only a small share of babies arrive on the exact date. Most are born within about two weeks either side. A scan by your doctor gives a more reliable dating, especially if your cycles are irregular.
A worked example
If the first day of the last period was 1 January 2026, adding 280 days gives an estimated due date of 8 October 2026. A pregnancy of 37 to 42 weeks is considered full term, so a baby arriving anywhere in that window is normal.
Cycle length
The calculation assumes a regular 28-day cycle. If your cycles are much longer or shorter, your doctor may adjust the date after an early scan.
