🤰 Due Date Calculator
When is your baby due?
How Due Dates Are Calculated
The standard calculation uses Naegele's Rule: add 280 days (40 weeks) to the first day of your last menstrual period. This assumes a 28-day cycle with ovulation on day 14. If your cycles are longer or shorter, your due date may shift by several days. Only 5% of babies arrive on their exact due date — most arrive within 2 weeks before or after.
First trimester: weeks 1-12. Second trimester: weeks 13-27. Third trimester: weeks 28-40. The heartbeat is detectable at 6 weeks. Sex is visible on ultrasound at 18-20 weeks. Viability outside the womb begins around 24 weeks. Full-term is 39-40 weeks.