Pregnancy Due Date Calculator

How Your Due Date is Calculated

Naegele's Rule

The standard calculation adds 280 days (40 weeks) to the first day of your last menstrual period. This assumes a 28-day cycle — the calculator adjusts for cycles that are shorter or longer.

How Accurate Is It?

Only about 4% of babies are born on their exact due date. Most arrive within 2 weeks either side. An ultrasound scan in the first trimester gives the most accurate dating.

Trimesters at a Glance

First trimester: weeks 1–12. Second trimester: weeks 13–26. Third trimester: weeks 27–40. Key scans typically happen at 8–12 weeks (dating scan) and 18–22 weeks (anatomy scan).