How an IVF due date is calculated
In IVF, fertilization happens on the day of egg retrieval. That day counts as conception, 2 weeks 0 days into the pregnancy, and the due date is 266 days later. An embryo transferred on day 3 or day 5 is already that many days old, so those days are subtracted. For a day-5 embryo the due date is 261 days after transfer; for a day-3 embryo, 263 days.1 The same rule gives 260 days for a day-6 embryo.
| Date you have | Embryo age | Days to due date |
|---|---|---|
| Egg retrieval | 0 days | 266 |
| Day-3 transfer | 3 days | 263 |
| Day-5 transfer | 5 days | 261 |
| Day-6 transfer | 6 days | 260 |
- May 8, 2026Day-5 embryo transfer date
- +266 days38 weeks from fertilization
- −5 daysEmbryo was already 5 days old
- =Sunday, January 24, 2027Estimated due date
- May 6, 2026Day-3 embryo transfer date
- +266 days38 weeks from fertilization
- −3 daysEmbryo was already 3 days old
- =Sunday, January 24, 2027Estimated due date
Both examples describe embryos fertilized on May 3, 2026, so they share a due date.
Fresh and frozen transfers
The calculation is the same for both. For a frozen embryo transfer, use the transfer date and the embryo’s developmental age when it was frozen. The time it spent frozen doesn’t count, so never use the freezing date.1
Your clinic’s date comes first
If your fertility clinic has given you a due date, use theirs. For pregnancies conceived with assisted reproduction, the due date should come from the IVF dates and is not usually changed after later ultrasounds.1
Donor-egg and gestational-carrier pregnancies are dated the same way: from the embryo’s age and transfer date, not from anyone’s last period.