Estimate your due date (EDD) from your IVF embryo transfer date. Works for Day 3 and Day 5 (blastocyst) transfers, and applies equally to fresh and frozen embryo transfer (FET) cycles.
Because IVF pregnancies begin from a precisely known embryo transfer date rather than an estimated ovulation date, your due date is calculated using the embryo's age at transfer. The standard rule (based on ACOG assisted reproductive technology dating guidance) is: EDD = transfer date + (266 − embryo age in days). For a Day 5 blastocyst transfer this works out to transfer date + 261 days; for a Day 3 cleavage-stage transfer it's transfer date + 263 days. The same rule applies whether the embryo was fresh or frozen (FET), because what matters is the embryo's biological age, not when it was frozen.
⚕️ Medical Notice: This calculator provides an estimate only. It cannot account for twins, multiples, or pregnancy complications, all of which can change the likely delivery timing. Your fertility clinic's dating, based on your specific transfer and any follow-up ultrasounds, should always take priority over this tool. Consult your fertility specialist or obstetrician for medical advice.
3 = Day 3 cleavage-stage embryo, 5 = Day 5 blastocyst. Other values (e.g. 2 or 6) are sometimes used for frozen transfers.
Informational only — the due date formula is identical for fresh and frozen transfers once the transfer date and embryo age are known.
| Detail | Value |
|---|
IVF pregnancies are dated differently from natural conceptions because the exact age of the embryo on transfer day is known precisely, rather than estimated from a last menstrual period. Obstetric dating conventions (reflected in ACOG's assisted reproductive technology guidance) treat a full-term pregnancy as running 266 days from the notional day of fertilisation (or, for a natural cycle, from ovulation). An embryo transferred on Day 3 is already 3 days past fertilisation; a Day 5 blastocyst is already 5 days past fertilisation. So instead of counting forward from ovulation, the calculator counts forward from the transfer date, adjusted for however many days of embryo development have already happened in the lab.
The two-day difference between a Day 3 and a Day 5 due date comes directly from embryo age at the moment of transfer. A Day 5 blastocyst has already completed two more days of development outside the body than a Day 3 embryo has, so fewer days need to be added after transfer to reach the same 266-day total pregnancy length. This is not a different pregnancy length — it is the same 266-day convention, just measured from two different starting points.
The due date formula is exactly the same for fresh and frozen embryo transfers. What determines the calculation is the embryo's developmental age on the day it is placed in the uterus — not whether it was ever frozen, or how long it spent frozen beforehand. A Day 5 blastocyst that was frozen for two years and then thawed and transferred is still dated as a Day 5 transfer on the day of transfer, using exactly the same EDD = transfer date + 261 days rule. This is one of the practical advantages of IVF dating: it does not rely on estimating when a cycle "would have" ovulated.
Once a due date convention is set, gestational age is counted the same way as in any pregnancy — from a notional "day 0", set 266 days before the due date (equivalently, embryo age in days before the transfer date). Gestational age is expressed in completed weeks and days, and the pregnancy is divided into three trimesters:
| Trimester | Gestational Age Range |
|---|---|
| First trimester | 0 weeks 0 days – 13 weeks 6 days |
| Second trimester | 14 weeks 0 days – 27 weeks 6 days |
| Third trimester | 28 weeks 0 days onward |
In a natural conception, doctors typically estimate a due date from the first day of the last menstrual period (LMP), assuming a textbook 28-day cycle with ovulation on day 14 — an assumption that does not hold for every woman. IVF removes much of that guesswork. Because the embryo transfer date and the embryo's exact age (Day 3 or Day 5) are recorded precisely by the fertility clinic, the due date can be calculated directly from known facts rather than an assumed ovulation day. This is why fertility clinics and obstetricians treat IVF dating as a reliable, and often preferred, method of establishing a due date.
The due date formula itself does not change if more than one embryo is transferred or if a single transfer results in twins (which can happen with identical twinning from one blastocyst). What does change is the likely actual delivery timing: twin and higher-order multiple pregnancies are, on average, delivered earlier than singleton pregnancies, often several weeks before the calculated EDD. If you are carrying twins or multiples from IVF, your obstetrician will typically set a revised target delivery window based on your specific pregnancy, rather than relying on the standard singleton due date estimate.
How does an IVF due date differ from natural conception dating?
Natural conception dating usually starts from the first day of your last menstrual period (LMP) and assumes ovulation happened around day 14 of a 28-day cycle — an estimate that can be inaccurate if your cycle is longer, shorter, or irregular. IVF dating instead starts from the embryo transfer date and the embryo's known age (Day 3 or Day 5), which are exact facts recorded by your fertility clinic rather than assumptions. This generally makes IVF due dates more reliable from the outset.
Why does a Day 3 transfer give a different due date than a Day 5 transfer?
A Day 5 blastocyst has already spent two more days developing outside the body than a Day 3 embryo has by the time it is transferred. Since both are dated using the same 266-day total pregnancy length from fertilisation, fewer days need to be counted forward after a Day 5 transfer to reach that same endpoint. This is why a Day 5 transfer adds 261 days from the transfer date, while a Day 3 transfer adds 263 days — a two-day difference that reflects embryo age, not a different pregnancy length.
Are IVF due dates more accurate than LMP-based due dates?
Generally, yes. Because the exact date of embryo transfer and the embryo's precise age are known and recorded by the fertility clinic, IVF dating removes the guesswork involved in estimating ovulation from a last menstrual period. LMP-based dating assumes a standard cycle length and ovulation day, which does not hold true for everyone. This is one reason fertility clinics and obstetricians often treat IVF-derived due dates as a dependable starting point, sometimes confirmed further with an early dating ultrasound.
Does the due date formula change for frozen embryo transfers (FET)?
No. The formula is identical for fresh and frozen embryo transfers: EDD = transfer date + (266 − embryo age in days at transfer). What matters is the embryo's developmental age on the day it is placed in the uterus, not whether it was ever frozen or how long it remained frozen beforehand. A Day 5 blastocyst that was frozen and later thawed for transfer is dated exactly the same way as a fresh Day 5 transfer.
Does having twins from IVF change my due date?
The due date calculation itself does not change based on how many embryos were transferred. However, twin and higher-order multiple pregnancies are, on average, delivered earlier than singleton pregnancies — often several weeks before the calculated EDD. If you are expecting twins or multiples, your obstetrician will typically set an individualised expected delivery window rather than relying on the standard singleton estimate this calculator provides.
What if my transfer was on a day other than Day 3 or Day 5?
The same formula works for any embryo age at transfer — simply enter the actual number of days as recorded by your clinic (for example, 2 or 6 for some frozen transfer protocols). The calculator subtracts that embryo age from 266 to determine how many days to add to your transfer date. If you are unsure of your embryo's exact age at transfer, check your clinic paperwork or ask your fertility team directly.
How is gestational age counted in an IVF pregnancy?
Gestational age is counted from a notional "day 0" of the cycle, which is set the same number of days before your transfer date as your embryo's age at transfer (for example, 5 days before a Day 5 transfer). From that notional day 0, gestational age is expressed in completed weeks and days, exactly as it would be for a naturally conceived pregnancy, and is used to track trimester progress and expected milestones.
Can my due date change after an early ultrasound?
It's possible, though less common with IVF pregnancies than with naturally conceived ones. Because the transfer date and embryo age are already precisely known, an early dating ultrasound in an IVF pregnancy usually confirms the calculated due date rather than significantly changing it. If there is a discrepancy, your clinic or obstetrician will advise which dating to use going forward.
Is this calculator suitable for IUI or natural cycle pregnancies?
This calculator is specifically designed for IVF pregnancies where an embryo transfer date and embryo age are known. For IUI (intrauterine insemination) or natural conception, due dates are usually estimated from the last menstrual period or an estimated ovulation/conception date instead — MegaCalcOnline's Due Date Calculator and Conception Calculator are better suited to those situations.
What should I do if this calculator's due date doesn't match my clinic's due date?
Always follow the due date provided by your fertility clinic or obstetrician. They may adjust your dating based on early ultrasound measurements, specific protocol details, or other clinical factors that a general calculator cannot account for. This tool is intended to help you understand how IVF due dates are worked out, not to override your clinic's own assessment.