The pregnancy due date calculator estimates the expected due date (EDD) using Naegele's rule — adding 280 days (40 weeks) to the first day of the last menstrual period. This is the standard method used in midwifery and obstetric practice worldwide. The calculator also displays the current gestational age in weeks and days and the number of days remaining until the estimated due date. Only approximately 5% of babies are born on their exact EDD; most arrive within 2 weeks either side.
| Milestone | Gestational Age |
|---|---|
| Positive pregnancy test | ~4 weeks |
| Heartbeat visible on ultrasound | 6–7 weeks |
| End of first trimester | 13 weeks |
| Anatomy scan | 18–20 weeks |
| Viability (preterm survival possible) | 24 weeks |
| End of second trimester | 27 weeks |
| Full term | 39–40 weeks |
| Post-term | ≥42 weeks |
Add 280 days (40 weeks) to the first day of your last menstrual period. This is Naegele's rule and assumes a 28-day cycle with ovulation on day 14. For cycles longer or shorter than 28 days, the estimated due date may be adjusted by ultrasound.
Gestational age is the number of weeks and days since the first day of the last menstrual period — not since conception. A pregnancy is considered full term at 39–40 weeks. Preterm birth is before 37 weeks; post-term is 42 weeks or beyond.