Health
Pregnancy Due Date Calculator
Estimated due date, current week of pregnancy, and trimester.
How the due date is calculated
Naegele's Rule: add 280 days (40 weeks) to the first day of your last menstrual period. This assumes a 28-day cycle and ovulation on day 14. Only about 5% of babies are born on their exact due date — the normal range is 37–42 weeks.
Trimester breakdown
- 1st Trimester: Weeks 1–12
- 2nd Trimester: Weeks 13–26
- 3rd Trimester: Weeks 27–40
Key milestones
- Week 8: Heartbeat detectable by ultrasound
- Week 12: End of highest-risk period
- Week 20: Anatomy scan
- Week 37: "Full term" begins
Frequently asked questions
How accurate is a due date calculation?▾
Calculated due dates are estimates. A first-trimester ultrasound is more accurate. Only 5% of babies arrive on their exact due date; 80% arrive within 2 weeks either side.
✓ Math logic verified against primary sources
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