IVF Due Date Calculator
With IVF the date of fertilisation is known to the day, so this is the one due date that does not rest on a remembered period.
Your IVF timeline
Gestational age is counted from 14 days before egg retrieval, which is why the clock was already running at transfer.
The formula
Due date is the transfer date plus 266 days, minus the age of the embryo in days.
| Transfer | Add to transfer date | Why |
|---|
| Day 3 embryo | 263 days | 266 minus 3 days in the lab |
| Day 5 blastocyst | 261 days | 266 minus 5 |
| Day 6 blastocyst | 260 days | 266 minus 6 |
| Egg retrieval | 266 days | Retrieval is day 0 |
Fresh or frozen makes no difference. An embryo that spent three years in storage and one transferred the same week give the same due date, because only its age at transfer counts.
Why you were already pregnant at transfer
Obstetric dating counts from the first day of the last period, about two weeks before conception. To keep IVF pregnancies on the same scale, the clock starts 14 days before egg retrieval.
So on the day of a day-5 transfer you are already 2 weeks and 5 days pregnant, before the embryo has implanted. Every IVF patient does a double take at this. Nothing is wrong; the convention is just borrowed from cycles you did not have.
This is also why your dating scan usually agrees closely with the calculated date. With natural conception the scan often moves the date by several days. With IVF there is nothing to correct.
Questions people actually ask
Does a frozen transfer change the due date?
No. Only the embryo's age on transfer day matters. Time in storage does not count, because the embryo is not developing while frozen.
How many weeks pregnant am I after a day-5 transfer?
Two weeks and five days on transfer day itself. The table above tracks it from there.
When is the beta hCG test?
Your clinic sets it, usually somewhere between 9 and 14 days after transfer. Home tests before that can pick up leftover trigger shot hCG and give a false positive, which is why clinics ask you to wait.
Does the due date change for twins?
The calculation does not change, but the outcome does. Twins commonly arrive around 37 weeks rather than 40, and your clinic will plan around that instead of the calculated date.
My clinic gave me a different date. Who is right?
Your clinic. If their date differs by more than a day or two, they have probably adjusted after a dating scan, and that measurement beats arithmetic. Use theirs for anything that matters.