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IVF Due Date Calculator Guide
IVF due dates are more precise than natural-conception ones, because the date of fertilisation is known exactly rather than estimated. This calculator works from your transfer or retrieval date.
Due date = Transfer date + 266 − embryo age in days
Day-5 blastocyst: transfer + 261
Day-3 transfer: transfer + 263
Egg retrieval: retrieval + 266
Why IVF Dating Is Better
Ordinary pregnancy dating rests on two guesses: that you remember your period start correctly, and that you ovulated on day 14. Both are often wrong.
With IVF, neither guess is needed. Fertilisation happened in a lab on a known date, and the embryo's age at transfer is known to the day. That's why IVF due dates rarely get revised at the dating scan — there's nothing to correct.
Why Subtract the Embryo's Age
This is the bit that confuses people. Pregnancy runs about 266 days from fertilisation. A day-5 blastocyst has already been alive five days when it's transferred — so from the transfer date there are only 261 days left to go. Transfer a day-3 embryo and 263 days remain.
Get this backwards and you'll be out by nearly a week in the wrong direction.
Frozen Transfers Work the Same Way
Freezing stops the clock completely. An embryo frozen at day 5 and thawed two years later is still a day-5 embryo. Use the transfer date and the embryo's age at freezing — the time in storage is irrelevant to the maths.
Your Clinic's "Weeks" Will Look Odd
Clinics report gestational age using the same LMP convention as everyone else, which means they back-calculate a period date you never had. Day-5 transfer day is counted as 2w5d pregnant — before the embryo was even inside you.
It's not an error. It exists so IVF pregnancies slot into the same charts, scan schedules and screening windows as everyone else's.
The Beta Test
Clinics typically test hCG around 9–11 days after a day-5 transfer. Home tests before then produce the false negatives and false positives that make the two-week wait so unpleasant — trigger shots contain hCG and can still be in your system. Go with your clinic's date.
Once you have a due date, track progress with the pregnancy week calculator.
This is an estimate for general information, not medical advice. Every pregnancy and every cycle is different, and only your doctor or midwife can give you dates and guidance for your situation. Nothing here replaces professional care.
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