Because IVF pins down the exact day of fertilization and transfer, your due date can be calculated with unusual precision. Enter your details below to see it.
Frozen transfers (FET) use the same rule — pick the age the embryo was at freezing.
Retrieval day counts as the day of fertilization (day 0 of embryo development).
For a pregnancy conceived naturally, the due date is really an educated guess. Providers count forward from the first day of your last menstrual period (LMP) and assume that ovulation — and therefore fertilization — happened about 14 days later. For many people that assumption is off by several days, because ovulation can come early or late and cycles vary from person to person. That single guess is the largest source of uncertainty in ordinary pregnancy dating.
IVF removes the guesswork. In an IVF cycle, the laboratory documents the exact day the egg was retrieved and fertilized, and the exact day the embryo was transferred back to the uterus. There is no need to estimate when ovulation occurred, because the biology that is normally hidden inside the body happened — and was recorded — in the clinic. Knowing the precise age of the embryo means the math can start from a firm, dated point rather than a moving target.
The result is a due date you can trust more than most. It still describes a 40-week estimate rather than a guaranteed delivery day, but the starting point is solid. Everything in this calculator runs in your browser; nothing you enter is stored or sent anywhere.
Pregnancy runs about 266 days (38 weeks) from fertilization to birth, and about 280 days (40 weeks) when counted from the LMP. IVF lets us anchor to the fertilization side of that equation. The general rule for an embryo transfer is simple: start from the transfer date, add the full 266 days, then subtract the embryo's age, because part of that development already happened in the lab.
Due date = transfer date + 266 − embryo age · (retrieval date + 266 when dating from egg retrieval)
Here is how that plays out for the most common scenarios. A Day-5 blastocyst is already five days into development at transfer, so you add fewer days; a Day-3 embryo is only three days along, so you add slightly more.
| Starting point | Formula | Example (transfer/retrieval on Jan 1) |
|---|---|---|
| Day-5 transfer (blastocyst) | Transfer date + 266 − 5 = +261 days | Due date about Sep 19 |
| Day-3 transfer (cleavage stage) | Transfer date + 266 − 3 = +263 days | Due date about Sep 21 |
| Egg retrieval | Retrieval date + 266 (retrieval = fertilization day) | Due date about Sep 24 |
| Frozen transfer (FET) | Same embryo-age rule as a fresh transfer | Day-5 FET → +261; Day-3 FET → +263 |
The calculator also converts your due date into a "dating LMP" date (the due date minus 280 days) so it lines up with the week-by-week numbers you'll hear at appointments, and it shows your current gestational age and trimester based on that timeline.
One of the most common questions is whether a frozen embryo transfer (FET) changes the math. It does not. What matters for dating is the embryo's developmental age at the moment it is transferred — not the calendar time it spent frozen. A blastocyst that was frozen on day 5 and later thawed and transferred is still dated as a Day-5 transfer, and a Day-3 embryo is dated as a Day-3 transfer.
This can feel counterintuitive, because a frozen embryo might have been created months or even years before the transfer. But freezing effectively pauses development. When the embryo is thawed, it resumes from exactly the stage at which it was frozen, so the pregnancy timeline begins at transfer using that same embryo age. Whether your cycle is fresh or frozen, the due date depends on the embryo age you select above.
Even with precise dates, your fertility clinic will confirm the pregnancy with an early ultrasound, usually a few weeks after a positive test. This scan checks that the pregnancy is in the right place, measures early growth, and — for many people — is the first chance to see a heartbeat. Because IVF dating is already accurate, the measurements typically match the calculated due date closely.
If the ultrasound measurements differ from the calculated date, your provider decides whether to adjust the due date. In IVF pregnancies this is uncommon, since the transfer and retrieval dates are known with certainty, but early growth can still vary a little from baby to baby. The guiding principle is simple: a calculator is a helpful preview, and your clinical team's assessment is the final word. Always follow your provider's dating over any estimate you generate here.
IVF pregnancies are more likely than average to involve twins or other multiples, especially when more than one embryo is transferred. The due date is still calculated the same way — from the transfer or retrieval date and embryo age — but it's worth knowing that twins and higher-order multiples commonly arrive earlier than a single baby.
That's not a reason for worry so much as a reason to plan. If you're expecting multiples, your provider will monitor the pregnancy more closely and talk with you about the likely timing of delivery, which is often several weeks before a 40-week due date. Treat the calculated due date as your reference point, and let your care team guide expectations about when your babies may actually arrive. As with all dating questions, defer to the professionals who are watching your pregnancy week by week.
IVF due dates are calculated from the embryo's known age instead of a guessed ovulation date. For an embryo transfer, the due date is the transfer date plus 266 days minus the embryo's age at transfer — so a Day-5 (blastocyst) transfer is 261 days out and a Day-3 transfer is 263 days out. For a fresh cycle dated from egg retrieval, retrieval day counts as the day of fertilization, so the due date is retrieval plus 266 days. Because the timing of fertilization is documented in the lab rather than estimated, these dates are unusually precise.
A standard due date works backward from the first day of your last period and assumes you ovulated on day 14 — an assumption that is wrong for many people. With IVF, the clinic knows the exact day the egg was retrieved and fertilized and the exact day the embryo was transferred, so there is no ovulation guesswork. That known fertilization date removes the biggest source of error in ordinary pregnancy dating.
No. A frozen embryo transfer uses the same rule as a fresh transfer: the due date depends on the embryo's age at the moment it is thawed and transferred, not on how long it was frozen. A thawed Day-5 blastocyst is dated as a Day-5 transfer, and a thawed Day-3 embryo is dated as a Day-3 transfer. The time spent in the freezer does not add to the pregnancy timeline.
Yes. Your fertility clinic and an early ultrasound are the final word on dating. Most clinics perform a first scan a few weeks after transfer to confirm the pregnancy is developing on schedule. Because your dates are already precise, the ultrasound usually matches the calculated due date closely — but if your provider adjusts it, follow their guidance over any calculator.
Probably not, and that's completely normal. A due date is a best estimate of a 40-week point, not a deadline. Only about 1 in 20 babies arrives on the exact due date; most healthy babies are born in the weeks around it. IVF dating tells you the target with confidence, but the actual birth day still depends on your body, your baby, and — for twins or multiples — how your pregnancy progresses.