Due date calculator
Enter the first day of your last period, or the conception date, to estimate the due date and see how far along you are.
Estimated due date
An estimate only. Your midwife or doctor will confirm the date, usually with an ultrasound scan.
How it works
due date = last period + 280 days + (cycle − 28)due date = conception + 266 daysFrequently asked questions
How is the due date calculated?
With Naegele’s rule: 280 days (40 weeks) after the first day of the last menstrual period, adjusted for cycles longer or shorter than 28 days. From a conception date it is 266 days later.
How accurate is it?
Only about 4% of babies are born on the due date; most arrive within two weeks of it. An early ultrasound scan gives the most reliable date.
When does each trimester start?
The second trimester starts at week 14 and the third at week 28, counted from the last period.