Due Date Estimation
EDD (estimated due date) is often calculated from the first day of the last menstrual period (LMP) using Naegele's rule:
EDD = LMP + 280 days (40 weeks)
Ultrasound in the first trimester can refine dating — early measurements are most accurate.
Only ~5% on the Exact Date
Term is 37–42 weeks for many classifications. Spontaneous labor on the exact EDD is uncommon — treat EDD as a 2-week window mentally.
Induction policies vary by hospital and region — medical indications drive timing.
Trimesters
| Trimester | Weeks (approx) |
|---|---|
| First | 0–13 |
| Second | 14–27 |
| Third | 28–birth |
Milestones (first kicks, glucose screening) map to these — your provider's schedule may differ slightly.
How to Use This Pregnancy Calculator
Enter LMP or conception date (if known) or ultrasound dating where supported. Review EDD, trimester, and milestone reminders — always follow your clinician's dating for medical decisions.