IVF Due Dates Explained

Guides. Updated October 11, 2026. Calculated with the standard pregnancy dating method used by ACOG and the NHS.

IVF due dates are calculated from the transfer date and the age of the embryo, because the day of fertilisation is known exactly.

The formula

Subtract the embryo's age (3, 5 or 6 days) from the transfer date to get the fertilisation date, then add 266 days. For a day 5 transfer, that's the transfer date plus 261 days.

Frozen transfers

For frozen embryos, use the embryo's age when it was frozen. The time in storage doesn't count.

Gestational age

Clinics still express IVF pregnancies in weeks from a notional last period, two weeks before fertilisation, so the weeks line up with any other pregnancy.

This article is general information, not medical advice. Talk to a doctor or midwife about your own pregnancy or fertility.