IVF due date calculation: day-3 vs day-5 transfers

Dating an IVF pregnancy is the one situation where the due date is genuinely precise. With natural conception, no one knows the exact day; with IVF, the embryo's age and the transfer date are recorded to the day, so the arithmetic has no guesswork in it.

The key insight: count from a known point

Every IVF date can be converted into an equivalent last menstrual period, after which the usual 280-day rule applies. The conversion depends on how old the embryo was when it was transferred, because a day-5 blastocyst is two days further along than a day-3 embryo.

The formulas

From the transfer or retrieval date:

• Day-5 (blastocyst) transfer: due date = transfer date + 261 days
• Day-3 (cleavage) transfer: due date = transfer date + 263 days
• Egg retrieval (day 0): due date = retrieval date + 266 days

These agree with a single general rule: equivalent LMP = transfer date − (14 + embryo age in days), then due date = equivalent LMP + 280. For a day-5 transfer that's transfer − 19 + 280 = transfer + 261, exactly as above. Our IVF mode applies whichever version matches the date you have.

Fresh vs. frozen transfers

The dating is the same for fresh and frozen embryo transfers, because it depends on the embryo's developmental age at transfer, not on whether it was frozen in between. A day-5 blastocyst is dated as a day-5 blastocyst whether it was transferred fresh or thawed from storage. What matters is the transfer date and the embryo's age that day.

Why gestational age still starts “before” the embryo existed

Because gestational age is counted from the equivalent last period — about two weeks before conception — an IVF pregnancy is already counted as roughly two weeks along at the moment of fertilisation. This is the same two-week offset that confuses everyone; it's explained in gestational age vs. fetal age. It keeps IVF pregnancies on the same clock as everyone else's, so screening windows and term definitions line up.

How accurate is it?

Very. Because the timing is known, an IVF due date typically doesn't need adjusting by ultrasound, though scans are still used to confirm development. If a scan and the IVF date disagree by only a day or two, the IVF date usually stands. As always, the estimate is a reference point — see how accurate is your due date — and your fertility clinic will confirm the dating.