IVF & Ultrasound Due Date Calculator

Frequently Asked Questions

How is the due date calculated for an IVF transfer?

For a Day-3 embryo, EDD = transfer date + 266 − 3 = transfer + 263 days. For a Day-5 blastocyst, EDD = transfer + 266 − 5 = transfer + 261 days. Egg-retrieval date + 266 days also works (retrieval = conception).

How does an early ultrasound refine the due date?

A first-trimester crown-rump length (CRL) measurement is plugged into the Robinson-Fleming formula: gestational age (days) = 8.052 × √(CRL mm) + 23.73. EDD = scan date + (280 − GA days).

When should the ultrasound EDD replace the LMP/IVF date?

ACOG keeps the IVF-derived date because conception timing is exact. For non-IVF pregnancies, ultrasound replaces LMP if CRL dating differs by more than 5 days before 9 weeks, 7 days at 9–13⁶ weeks, or 10 days at 14–15⁶ weeks.

How accurate is the EDD overall?

Only about 4–5% of babies are born on the exact EDD; ≈80% arrive within ±10 days. Treat the date as a midpoint of a window. This tool is informational - confirm dating with your fertility clinic or OB-GYN.

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Pregnancy & Baby Disclaimer: Educational only. Not medical advice.

This calculator is for general informational and educational purposes only and is not medical advice. It does not diagnose, treat, prevent, or replace care from your OB-GYN, midwife, pediatrician, or other qualified healthcare provider. Always consult your healthcare provider for any decisions about your pregnancy, your baby, or your postpartum recovery.

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How This Calculator Works

Standard due-date math (LMP + 280 days) assumes a regular 28-day cycle and a known last menstrual period. Those assumptions break for IVF pregnancies (no menses preceded conception) and for unsure LMP pregnancies where a first-trimester ultrasound becomes the authoritative dating tool. This calculator handles both. The IVF mode uses the egg-retrieval date as a precise conception equivalent and offsets for the embryo's age at transfer (Day 3 cleavage-stage or Day 5/6 blastocyst). The ultrasound mode takes the crown-rump length (CRL) measured between roughly 7 and 13 weeks and applies the Robinson–Fleming formula adopted by ACOG, SMFM, and the AIUM as the first-trimester dating gold standard (accurate to ± 5–7 days when CRL is ≤ 84 mm).

Formula / Method

IVF: conception = transfer date − embryo age in days. EDD = conception + 266 days. So a Day-5 blastocyst transferred on July 1 puts conception (retrieval) on June 26 and EDD on March 19 the following year. A Day-3 transfer on the same July 1 puts conception on June 28 and EDD on March 21. Gestational age at the moment of transfer = (embryo age + 14) ÷ 7 weeks - the “+14” converts from conception age to obstetric (LMP-based) age. Ultrasound: Robinson–Fleming (1975) - GA in days = 8.052 × √(CRL in mm × 1.037) + 23.73. EDD = ultrasound date + (280 − GA days). Example: CRL = 30 mm on March 1 → GA = 8.052 × √31.11 + 23.73 ≈ 68.6 days = 9w 6d → EDD ≈ March 1 + 211 days ≈ September 28.

Worked Example

A patient transfers a Day-5 blastocyst on January 10. Conception = January 5; EDD = January 5 + 266 = September 28. Gestational age at transfer = (5 + 14) ÷ 7 ≈ 2 weeks 5 days, so the standard “first missed period” sign is just over a week away. Now suppose at a viability scan on February 28 the embryo's CRL measures 12 mm. Robinson–Fleming gives GA = 8.052√(12×1.037) + 23.73 ≈ 8.052×3.525 + 23.73 ≈ 52.1 days = 7w 3d, EDD ≈ February 28 + (280−52) = October 13. Because ultrasound and IVF dating differ by > 7 days here, your provider would typically retain the IVF date as the most reliable.

Common Mistakes

Using the “LMP” reported by the IVF clinic for downstream calculators - many clinics use the retrieval-minus-14 convention, which is correct but inconsistent with home pregnancy calculators that assume true menses.

Forgetting the embryo age offset - a Day-5 transfer is biologically 5 days older than a Day-3 transfer; treating them identically miscounts by 2 days.

Using a CRL > 84 mm in Robinson–Fleming - after about 13 weeks the formula loses accuracy; biparietal diameter, head circumference, and femur length become the dating measurements.

Overriding ultrasound dating with LMP dating - ACOG advises adopting the ultrasound EDD when the discrepancy exceeds 7 days in the first trimester (or 10–14 days in mid-second trimester).

Treating EDD as a deadline - only ≈ 4–5% of pregnancies deliver exactly on EDD; ≈ 80–90% deliver within the ± 2-week window around it.

Tips & FAQ

Which date wins, IVF or ultrasound? IVF dating is the most precise possible (the moment of conception is literally known), so an early ultrasound that disagrees within a few days should usually not override it. Beyond ≈ 7-day disagreement, discuss with your provider. Frozen embryo transfers (FET)? Use the actual FET date as the transfer date and the embryo's age in days at thaw/transfer as the embryo-age input. Why 266 days from conception? The standard 280-day Naegele's rule counts from LMP, about 14 days before ovulation/conception; subtracting those 14 days gives 266 days of true gestation. Why is CRL the dating standard? First-trimester growth is tightly regulated by genetics, almost independent of maternal nutrition or pathology, so CRL maps very predictably onto gestational age - later in pregnancy that link weakens. This tool is an estimate, not a medical determination; consult your healthcare provider, who will integrate your full clinical picture with imaging to set your official EDD.

IVF & Ultrasound Due Date Calculator

Frequently Asked Questions

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