Due Date from Conception Calculator
Know your conception date? Enter it here to calculate your estimated due date and current gestational age — ideal for IVF and tracked ovulation cycles.
Fetal Age vs. Gestational Age
| Gestational Age (LMP) | Fetal Age (Conception) | Milestone |
|---|---|---|
| 4 weeks | 2 weeks | Implantation |
| 6 weeks | 4 weeks | Heartbeat detectable |
| 10 weeks | 8 weeks | Embryo → fetus |
| 13 weeks | 11 weeks | End of 1st trimester |
| 20 weeks | 18 weeks | Anatomy scan |
| 40 weeks | 38 weeks | Full term / due date |
Medical gestational age is always measured from LMP — 2 weeks more than fetal/conception age. For informational purposes only.
Frequently Asked Questions
How is due date calculated from conception?
From conception, a full-term pregnancy is 266 days (38 weeks). This is the fetal age. Your estimated due date = conception date + 266 days. However, medical gestational age is measured from LMP (last menstrual period), which is approximately 14 days before conception. So gestational age = fetal age + 14 days. A 38-week fetus has a gestational age of 40 weeks. This is why doctors say pregnancy is 40 weeks even though fertilization-to-birth is only 38 weeks.
How do I know my conception date?
Conception date is the date of fertilization — which occurs within 12–24 hours after ovulation. Methods to estimate it: (1) Ovulation tracking: if you used LH predictor strips or temperature tracking, ovulation day is your approximate conception date. (2) IVF transfer date: for IVF pregnancies, your clinic will provide the fertilization date. (3) From LMP: if you know your LMP and have a 28-day cycle, conception was approximately day 14 of your cycle. (4) Ultrasound back-calculation: early ultrasound can estimate gestational age, from which conception date can be inferred.
What is the difference between gestational age and fetal age?
Fetal age (embryonic age) = weeks since fertilization/conception. Gestational age = weeks since last menstrual period (LMP) = fetal age + 2 weeks. All medical milestones use gestational age. When your doctor says you are '10 weeks pregnant,' they mean 10 weeks since your LMP — or about 8 weeks since conception. Ultrasounds measure gestational age. If you track your conception date precisely (e.g., through IVF or ovulation testing), this calculator correctly adds 2 weeks to convert to gestational age.
How accurate is an early ultrasound for dating?
A first-trimester ultrasound (7–10 weeks) is the gold standard for pregnancy dating, with a margin of error of ±5–7 days. The crown-rump length (CRL) is measured and compared to population averages. If the ultrasound date disagrees with your LMP-based date by more than 7 days (first trimester) or 14 days (second trimester), your OB may revise your due date based on the ultrasound. After 20 weeks, dating accuracy decreases significantly (±2–3 weeks). If you conceived via IVF, the embryo transfer date is the most precise starting point.