Reviewer: Dr. Ruqaiya Khan, MD, FACOG. Final clinical review of this article is pending. The dating method below follows ACOG guidance.
Your IVF due date is calculated from your embryo transfer date: add 263 days to a day-3 transfer, 261 days to a day-5 (blastocyst) transfer, or 260 days to a day-6 transfer. Unlike a natural pregnancy, where the due date is a best guess built on your last period, IVF gives you a documented starting point, so the estimate is more precise from day one.
This guide covers the formulas, a worked example, frozen embryo transfers (FET), IUI, why your ultrasound usually will not change the date, and what to expect with twins. If you just want the number, the IVF due date calculator does the math for you.
IVF Due Date Formulas at a Glance
| Embryo age at transfer | Add to transfer date | Gestational age on transfer day |
|---|---|---|
| Day 3 embryo | 263 days | 2 weeks 3 days |
| Day 5 blastocyst | 261 days | 2 weeks 5 days |
| Day 6 blastocyst | 260 days | 2 weeks 6 days |
| Egg retrieval / fertilization date (day 0) | 266 days | 2 weeks 0 days |
| IUI day (day 0) | 266 days | 2 weeks 0 days |
How Is an IVF Due Date Calculated?
A full-term pregnancy lasts about 266 days (38 weeks) from fertilization, which is the same as 280 days (40 weeks) from the first day of a typical 28-day cycle. In IVF, fertilization happens in the lab on a known date, and the embryo has a known age on the day it is transferred. So the due date is simply:
Due date = transfer date + 266 days − age of the embryo in days
This is the method ACOG recommends for pregnancies conceived with assisted reproductive technology, and it applies to both fresh and frozen cycles. Because the embryo’s age is subtracted, a day-5 embryo gives 266 − 5 = 261 days.
Clinics also work out an equivalent LMP date: the due date minus 280 days. It is not a real period. It simply lets your pregnancy be tracked on the same week-by-week scale as every other pregnancy, which is why you are counted as 2 weeks 5 days pregnant on the day of a day-5 transfer.
How to Calculate It Step by Step
- Find your embryo’s age from your clinic paperwork: day 3 (cleavage stage), day 5, or day 6 (blastocyst).
- Note your transfer date. For a frozen embryo, this is the thaw-and-transfer date, not the date it was frozen.
- Add 263 days (day 3), 261 days (day 5), or 260 days (day 6) to the transfer date.
- Check the result against the date your clinic gives you, and treat your clinic’s date as the official one.
Worked Example
Suppose your embryo transfer is on October 10, 2026:
- Day-3 transfer: October 10, 2026 + 263 days = June 30, 2027
- Day-5 transfer: October 10, 2026 + 261 days = June 28, 2027
- Day-6 transfer: October 10, 2026 + 260 days = June 27, 2027
Notice that the older the embryo, the fewer days you add. A day-5 embryo has already completed two more days of development than a day-3 embryo, so the finish line comes two days sooner. For the day-5 example, the equivalent LMP date is September 21, 2026 (June 28, 2027 minus 280 days).
Frozen Embryo Transfer (FET) Due Dates
A frozen embryo transfer uses the same formulas. Freezing pauses development, so what counts is the embryo’s age when it was frozen, not how long it sat in storage. A blastocyst frozen on day 5 and thawed for transfer is treated as a day-5 embryo, so you add 261 days to the transfer date. If your embryo was frozen on day 6, add 260 days.
In a medicated FET cycle, the transfer date is scheduled around your progesterone start date, so it should line up with the embryo’s age. If you are unsure whether you had a day-5 or day-6 embryo, ask your clinic before relying on a calculator.
Due Date After IUI
Intrauterine insemination (IUI) has no embryo age, so the count starts from the insemination day. Add 266 days to the IUI date. For an IUI on October 10, 2026, that gives July 3, 2027. If ovulation was tracked closely, your clinic may refine the date from the ovulation day. You can compare methods with the due date calculator.
Why IVF Dating Is More Precise Than LMP Dating
Standard due date calculators assume ovulation on day 14 of a 28-day cycle. Many people ovulate earlier or later than that, which is why LMP-based estimates can be off by a week or more. With IVF there is no ovulation guesswork: the egg retrieval and fertilization dates are recorded, and the embryo’s age at transfer is documented by the lab. To see how the two approaches differ, read traditional vs. IVF due date calculation.
Researchers rely on this accuracy too. A Monash University team built an ultrasound reference chart for 6 to 9 week pregnancies from more than 1,200 IVF pregnancies precisely because their true gestational age was known.
Will an Ultrasound Change My IVF Due Date?
Usually not. The American College of Obstetricians and Gynecologists (ACOG) advises that pregnancies conceived with assisted reproductive technology should be dated using the embryo’s age and transfer date. Early scans are mainly used to confirm a heartbeat, count the babies, and check that growth is on track.
If a scan measures noticeably ahead of or behind your IVF dates, your care team will look at the whole picture, including scan quality and timing, before deciding whether anything changes. For example, one hospital guideline asks clinicians to review the dating when the ultrasound differs from the transfer-based date by more than 6 days. A baby measuring a few days big or small on its own is normal variation and is not a reason to change the date. Learn more about gestational age and how it is tracked.
IVF Due Dates for Twins and Multiples
The same formulas give the estimated due date for twins, but that date is a calendar reference point, not a delivery target. Twin pregnancies commonly end earlier than singleton pregnancies, and timing depends on how the babies share the placenta and amniotic sac. One obstetric guideline suggests uncomplicated dichorionic (separate placentas) twins are usually delivered between 37 weeks 0 days and 38 weeks 6 days, while uncomplicated monochorionic-diamniotic twins may be delivered between 34 weeks 0 days and 37 weeks 6 days. Your obstetrician will plan the timing with you.
Is Your IVF Due Date Exact?
No. Even with perfect dating, a due date is the midpoint of a window, not a deadline. Only a small share of babies arrive on the exact day. ACOG defines early term as 37 weeks 0 days through 38 weeks 6 days, full term as 39 weeks 0 days through 40 weeks 6 days, and late term as 41 weeks 0 days through 41 weeks 6 days. With a due date of June 28, 2027, full term runs from June 21 to July 4, 2027, so most families will meet their baby within a few weeks either side of the estimate.
Calculate Your IVF Due Date Now
Enter your transfer date and embryo age into the IVF due date calculator to see your estimated due date, your current gestational age, and key milestone dates. Once you have your date, browse the pregnancy week-by-week guide to see what happens at each stage. Always confirm the final date with your fertility clinic or OB-GYN.
IVF Due Date FAQs
How many days do I add to a 5-day embryo transfer?
Add 261 days to the transfer date of a day-5 blastocyst. For a day-3 embryo add 263 days, and for a day-6 blastocyst add 260 days.
How many weeks pregnant am I on transfer day?
Pregnancy is counted as if it began two weeks before fertilization. On the day of a day-5 transfer you are counted as 2 weeks 5 days pregnant, on a day-3 transfer 2 weeks 3 days, and on a day-6 transfer 2 weeks 6 days. This is the dating convention, not a sign that anything happened earlier.
Is the due date different for a frozen embryo transfer (FET)?
The method is the same. You use the embryo’s age when it was frozen together with the transfer date, so a day-5 frozen blastocyst still means transfer date plus 261 days.
How do I calculate a due date after IUI?
With intrauterine insemination (IUI) there is no embryo age to subtract. Count the insemination day as day 0 and add 266 days. Your clinic may adjust this if ovulation timing was monitored closely.
How accurate is an IVF due date?
It is one of the most reliable dating methods because fertilization and embryo age are documented. It is still an estimate: only a small share of babies arrive on the exact day, and full term spans 39 weeks 0 days through 40 weeks 6 days.
Why does my clinic’s due date differ from the calculator?
Small differences usually come from the embryo day entered, or from a clinic using a slightly different convention. Your clinic’s date is the one to follow.
Will my due date change after the first ultrasound?
Usually not. For IVF pregnancies the embryo-age date is normally kept, and an early scan is used to confirm viability and the number of babies. Your care team will only review the date if the scan differs substantially from the transfer-based date.
Can my IVF baby be born before the due date?
Yes. Many babies arrive in the weeks before or after the estimate, and twins often arrive earlier. Call your care team about regular contractions, fluid leaking, bleeding, or a drop in baby movement rather than waiting for the date.
Sources
- ACOG Committee Opinion No. 700: Methods for Estimating the Due Date
- NSW Health (SESLHD): Estimating the Due Date
- Ultrasound reference chart based on IVF dates to estimate gestational age at 6-9 weeks (PMC)
- CRICO / Harvard Medical Institutions: Management of Twins (obstetric guideline)
This page is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always consult your OB-GYN or midwife about your own pregnancy.
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