The formula doctors use
| Embryo at transfer | Due date |
|---|---|
| Day 5 (blastocyst) | Transfer date + 261 days |
| Day 3 | Transfer date + 263 days |
This is the method recommended by ACOG: with IVF, the date comes from the embryo’s age and the transfer date, not from a period.
Where 261 and 263 come from
A pregnancy is counted as 280 days from a “last period” start. A day-5 embryo is like day 19 of that count (280 − 19 = 261), and a day-3 embryo like day 17 (280 − 17 = 263).
Fresh, frozen and donor eggs
The same formula works for a fresh or a frozen embryo transfer, and with your own or donor eggs. Only two things count: the transfer date and the embryo’s age on that day.
How many weeks pregnant after a transfer
On the day of a day-5 transfer, you count as 2 weeks and 5 days pregnant. On the day of a day-3 transfer, you count as 2 weeks and 3 days. From there, the weeks go up like in any pregnancy, and the calculator shows your week today.
Questions people ask
How is an IVF due date calculated?
Add 261 days to the transfer date for a day-5 embryo, or 263 days for a day-3 embryo. This is the method in the ACOG guidance.
Is the date the same for a frozen embryo transfer?
Yes. What counts is the embryo’s age when it was transferred (day 3 or day 5) and the transfer date.
Does a donor egg change the due date?
No. The date comes from the embryo’s age and the transfer date, not from whose egg it was.
How many weeks pregnant am I after a transfer?
On transfer day you count as 2 weeks 5 days pregnant with a day-5 embryo, or 2 weeks 3 days with a day-3 embryo. The calculator shows your week today.
Is an IVF due date more accurate?
Yes. With IVF the embryo’s age is known, so the date is more exact than one based on a period (ACOG).
What about a day-6 blastocyst?
Our calculator covers day-3 and day-5 transfers, the ones in the ACOG guidance. For a day-6 transfer, your clinic will give you the date they use.
Why is my clinic’s date different?
Your clinic may count in its own way. Always follow the date your clinic, midwife or doctor gives you.
Read the full guide: IVF due date calculator
Sources
- ACOG Committee Opinion 700: Methods for Estimating the Due Date · checked October 24, 2026