Pregnancy Calculator

Pregnancy is counted from the first day of your last menstrual period (LMP) — not from conception. This is a medical convention used universally by obstetricians. Full-term pregnancy is 40 weeks (280 days) from LMP, though normal births occur anywhere from 37 to 42 weeks. How to calculate: Enter the first day of your last menstrual period. The calculator outputs: Estimated due date (EDD) — calculated using Naegele's rule: add 280 days to the LMP date (or add 9 months and 7 days). Current pregnancy week — how many complete weeks since LMP. Gestational age is expressed in weeks and days: "22 weeks + 3 days". Trimester — which trimester you are in: 1st trimester: Weeks 1-12. 2nd trimester: Weeks 13-27. 3rd trimester: Weeks 28-40. Key milestones: Week 6: Heartbeat often detectable by ultrasound. Week 10: First trimester screening window. Week 12: Nuchal translucency scan (NT scan). Week 20: Anatomy scan (anomaly scan). Week 28: Third trimester begins; glucose tolerance test. Week 36: Baby considered full-term soon; GBS test. Week 37: Early full-term begins. Week 40: Due date. Alternative starting points: If you know your conception date, enter it and the calculator adds 14 days (typical ovulation timing) to estimate LMP and due date. If you have your ultrasound-based gestational age, enter it with the scan date to work backward to your EDD.