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Free pregnancy calculator and due date calculator: estimate your estimated due date (EDD), gestational age, and trimester from last menstrual period (LMP), conception date, ultrasound dating, or IVF transfer. Perfect for planning prenatal visits, understanding pregnancy week by week, and pairing with our ovulation and due date tools.
Last updated: March 21, 2026 · For planning only—not a substitute for medical advice
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Your estimated due date (EDD) is the day around which your baby is expected—usually calculated as 40 weeks from the first day of your last menstrual period (LMP), or 38 weeks from conception (fetal age). Gestational age counts from LMP; clinicians use it for scheduling scans, genetic screening windows, and discussing fetal development. A good pregnancy calculator turns one known date (LMP, conception, ultrasound, or IVF transfer) into EDD, how many weeks pregnant you are today, and your trimester—so you can plan care and understand pregnancy week by week milestones.
Only a small fraction of babies arrive exactly on the EDD—but the date anchors your prenatal schedule, timing of the anatomy scan, glucose testing, and discussions about term vs early vs late pregnancy. Ultrasound dating in the first trimester often refines the EDD when LMP is uncertain or cycles are irregular.
This tool uses standard obstetric lengths: 280 days gestation from LMP (40 weeks) and 266 days from conception to EDD (38 weeks). Variables: LMP = first day of last period, C = average cycle length in days, U = ultrasound date, w, d = gestational age at ultrasound, T = embryo transfer date, e = embryo age in days (e.g. 5).
Last period (Naegele-style): EDD = LMP + 280 days + (C − 28)Conception: EDD = ConceptionDate + 266 daysUltrasound: days pregnant at scan = w×7 + d → EDD = U + (280 − days pregnant)IVF: EDD = T + 266 − e (e = days of embryo at transfer)From due date: Conception ≈ EDD − 266 daysGestational age today: ~280 − (days from today to EDD), then weeks + days; trimester 1 if <14 wk, 2 if 14–26, 3 if ≥27Edge cases: if "today" is before conception or far past EDD, the calculator clamps to sensible ranges. Your clinician may use different rules or chart-specific adjustments.
Illustrative scenarios using the same math as this page. Enter your real dates in the calculator for personalized results.
Trimester boundaries (gestational weeks, LMP dating)—useful alongside your due date calculator results for "what trimester am I in?"
| Trimester | Gestational weeks (approx.) | What it's often used for |
|---|---|---|
| First | 1 – 13 | Dating scan, early organogenesis, nausea peak for many |
| Second | 14 – 26 | Anatomy scan (~18–22 wk), glucose screening (often ~24–28 wk) |
| Third | 27 – 40+ | Growth checks, fetal movement counts, birth planning |
Exact visit timing varies by provider and country. Full-term is often considered from 37 weeks onward; post-term follow-up may start after 41 weeks depending on policy.
Educational only—your official EDD and gestational age are determined by your healthcare provider, especially with ultrasound or IVF records.
More tools: Pregnancy Conception Calculator · Due Date Calculator · Breastfeeding Calorie Calculator.
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