Calculate your EDD, current week, trimester, and key milestones
The most common method for calculating your estimated due date (EDD) is Naegele's Rule, which adds 280 days (40 weeks) to the first day of your last menstrual period. This assumes a 28-day cycle with ovulation on day 14. Our calculator adjusts for cycle lengths between 21–35 days.
Pregnancy is divided into three trimesters: the first trimester (weeks 1–13) when major organs develop, the second trimester (weeks 14–27) often called the "honeymoon period", and the third trimester (weeks 28–40) when the baby gains weight rapidly. Only about 5% of babies are born exactly on their EDD.
Key prenatal milestones include the first heartbeat detection around week 6, the anatomy scan at week 20, and the viability milestone at week 24. Full-term pregnancy is considered 37–42 weeks. Use this calculator as a guide, and always confirm your due date with your OB-GYN through ultrasound dating.