Work out your due date after a frozen embryo transfer. The dating is identical to a fresh transfer, what matters is the embryo's age on transfer day, not how long it was frozen.
| Input | Result |
|---|---|
| Day-5 FET on 10 March 2026 | Estimated due date 26 November 2026 |
| Day-3 FET on 10 March 2026 | Estimated due date 28 November 2026 |
| Day-6 FET on 10 March 2026 | Estimated due date 25 November 2026 |
This is the single most confusing point in IVF dating, and the answer is reassuringly simple: freezing pauses development, it does not advance it. A blastocyst vitrified on day 5 and thawed eleven months later is, for dating purposes, still a day-5 embryo on the day it goes back.
So the formula does not change at all, add 261 days for a day-5 FET, 263 for a day-3 FET and 260 for a day-6 FET, exactly as you would for a fresh transfer. What can feel strange is the calendar: a transfer in March might date a pregnancy from an embryo created the previous spring. That gap is real, and it is irrelevant to the arithmetic.
A natural-conception due date works backwards from the first day of your last period and assumes ovulation on day 14, an assumption that is wrong for a lot of people. IVF dating removes the guesswork, because the laboratory knows exactly how old the embryo was on the day it was transferred.
Everything follows from one rule. Convert the transfer date into an equivalent last menstrual period, then add the standard 280 days:
equivalent LMP = transfer date − (14 + embryo age in days)
due date = equivalent LMP + 280 days
which is the same thing as adding a fixed number of days to the transfer date:
| Starting point | Days to add | Why |
|---|---|---|
| Egg retrieval (day 0) | 266 | Retrieval stands in for ovulation, 14 days into a 280-day pregnancy |
| Day-5 embryo transfer | 261 | 266 − 5, the embryo is already five days old |
| Day-3 embryo transfer | 263 | 266 − 3 |
| Day-6 embryo transfer | 260 | 266 − 6 |
Clinical reference: ACOG Committee Opinion No. 700, Methods for Estimating the Due Date.
More reliable than any other method, because the inputs are recorded rather than recalled. IVF pregnancies rarely need a dating scan to establish the timeline, the scan confirms the dates rather than setting them, and where a scan and the IVF dates differ by only a day or two, the IVF date usually stands.
But a due date is still a median, not a deadline. Roughly one baby in twenty arrives on the date itself, most babies come between 37 and 41 completed weeks, and the term window shown above is the range that actually matters for planning. Multiples, more common after IVF — usually arrive earlier than a singleton would.
Not medical advice. This calculator does date arithmetic on the dates you enter, nothing more. It does not diagnose, does not assess a pregnancy and cannot account for your individual history. Your fertility clinic or midwife sets your official dating, and ultrasound findings can override any calculation. If anything here conflicts with what your care team told you, theirs is the date that counts.
No. The arithmetic is exactly the same as a fresh transfer. What matters is the embryo's developmental age on the day it is transferred, a blastocyst frozen at day 5 is still a day-5 embryo when it is thawed, so it is dated as one.
Because freezing effectively pauses development. An embryo frozen at day 5 resumes from exactly that stage when thawed, even if it was created months or years earlier. The pregnancy timeline starts at transfer, using the embryo's age that day.
Use the transfer date with the embryo's age if you have a frozen cycle, that is the precise anchor. If you are dating a fresh cycle, the retrieval date plus 266 days works just as well.
No. The medication protocol affects the lining and the timing of the transfer, not the embryo's developmental age, which is what dating uses.