How is the IVF due date calculated?
An IVF due date is calculated as 266 days from the date of conception (egg retrieval), which equals 40 weeks of gestation. For embryo transfers, you subtract the embryo's age from 266: a Day 5 blastocyst transfer is 261 days after transfer, a Day 3 transfer is 263 days, and an egg retrieval or IUI is 266 days.
Unlike a natural pregnancy — where the due date is estimated from the last menstrual period (LMP) with assumptions about when ovulation occurred — an IVF pregnancy has a known conception date. That makes the IVF due date one of the most precise estimates in obstetrics.
The calculator above uses the exact formula fertility specialists use worldwide. It accounts for embryo age at transfer, so a Day 5 blastocyst (already 5 days post-fertilisation) needs 5 fewer days than an egg retrieval to reach the same 266-day mark.
The IVF due date formula by procedure type
| Procedure | Days to add | Why |
|---|---|---|
| Egg retrieval / fertilisation | + 266 days | Day 0 of embryo development (conception) |
| IUI procedure | + 266 days | Approximate conception date |
| Day 3 embryo transfer (fresh or frozen) | + 263 days | 266 − 3 days of prior embryo growth |
| Day 5 blastocyst transfer (fresh or frozen) | + 261 days | 266 − 5 days of prior embryo growth |
| Day 6 blastocyst transfer | + 260 days | 266 − 6 days of prior embryo growth |
IVF due date vs natural pregnancy due date — which is more accurate?
The IVF due date is generally more accurate. With natural conception, doctors estimate the due date from the first day of your last menstrual period (LMP) using Naegele's rule. This assumes a regular 28-day cycle with ovulation on day 14, which doesn't apply to every woman. With IVF, the conception event happens in the embryology lab on a known date.
Important: only about 4–5% of babies are born on the exact estimated due date. Anywhere between 37 and 42 weeks is considered a normal full-term delivery window.
Does FET (frozen embryo transfer) change the calculation?
No. The formula is identical for fresh and frozen transfers — what matters is the embryo's age at the time of transfer, not whether it was frozen first. An embryo created six months ago, frozen, and transferred today is treated as a Day 3 or Day 5 embryo on the day of transfer.
Key pregnancy milestones after IVF
- Day 14 — Beta hCG blood test. The definitive first pregnancy test.
- Week 6 — First ultrasound. Confirms gestational sac and ideally a fetal heartbeat.
- Week 12 — End of first trimester. Miscarriage risk drops substantially.
- Week 20 — Anomaly scan. Detailed ultrasound checking fetal anatomy.
- Week 24 — Viability. Reasonable chance of survival with neonatal care.
- Week 37 — Full term. Baby is fully developed.
Twins and triplets — does the due date change?
The estimated due date is calculated identically for singletons, twins and triplets. However, multiple pregnancies are almost always delivered earlier for safety. Twins are typically delivered between 35 and 37 weeks. Triplets are usually delivered between 32 and 34 weeks.
Planning maternity care after IVF
IVF pregnancies need the same care as any other pregnancy, but doctors often recommend slightly more cautious early monitoring. At Shradha IVF & Maternity in Patna, Dr. Shradha Chakhaiyar personally manages the transition from IVF to pregnancy care. Book your first antenatal consultation as soon as your beta hCG is positive.
