IVF Due Date Calculator: Day 3 vs Day 5

IVF is the one situation where the conception date is not estimated but recorded, which makes the dating better than anything a calendar or a scan can offer. Enter the transfer date and whether the embryo was day 3 or day 5.

Transfer date plus 261 or 263 days

ACOG’s rule is that when a pregnancy results from assisted reproductive technology, the ART-derived gestational age assigns the due date, using “the age of the embryo and the date of transfer.” It then gives the two numbers outright:

Embryo at transfer	Due date
Day 5 (blastocyst)	transfer date + 261 days
Day 3 (cleavage stage)	transfer date + 263 days

The logic behind both is a single subtraction. Counting from fertilization, a term pregnancy is 266 days. A day-5 blastocyst has already used five of them before transfer, leaving 261; a day-3 embryo has used three, leaving 263. Under the hood the calculator reconstructs the equivalent last-period date — transfer, minus the embryo’s age, minus 14 days — so the gestational age it reports lines up with everyone else’s clock.

Worked example. A day-5 blastocyst transferred on June 20:

• 261 days later gives a due date of March 8 the following year.
• The equivalent last period would be June 1, and June 1 plus 280 days lands on the same day.
• Had it been a day-3 embryo, the due date would be March 10 — two days later.

Day-6 blastocysts and frozen transfers

Some blastocysts are not ready on day 5 and are transferred or vitrified on day 6. ACOG lists only the day-3 and day-5 figures, but the same subtraction extends cleanly: a day-6 embryo has consumed six of the 266 days, so the due date is transfer plus 260 days. In the calculator above, choose day 5 and read one day earlier — and confirm the figure with the clinic, which reports a due date of its own.

Frozen embryo transfer changes nothing in this arithmetic. Time spent in storage is not gestational time. What matters is the developmental day the embryo had reached when it was frozen and transferred, so a thawed day-5 blastocyst is dated exactly like a fresh one.

Why the ultrasound does not overrule this

For a spontaneous pregnancy, the whole point of an early scan is to correct a guess about ovulation, and the thresholds on due date by ultrasound say when it should. In IVF there is no guess to correct: fertilization happened in a lab on a documented date. This is why the ISUOG twin guidelines carve out the same exception, recommending that pregnancies conceived by IVF be dated using the age of the embryo and the date of transfer rather than by crown-rump length.

An early scan still matters — it confirms an intrauterine pregnancy, counts the embryos, and in twins establishes chorionicity — but it is not there to move the date.

If you are carrying more than one, the birth week is the number to plan around, and that is on the twin due date calculator. For the same conversion the other way around, see due date by conception date.

This content is informational and does not replace the care of your fertility clinic and your prenatal team, who assign the date of record.