IVF Due Date Calculator: How It Works
Reviewed by Safi Allah Khan
Medically reviewed by: Safi Allah Khan · Written by the Momi team · Last updated 20 October 2026
Quick answer: An IVF due date calculator adds 266 days minus the embryo's age to your transfer date. For a day-5 blastocyst transfer, that's transfer date + 261 days. For a day-3 transfer, it's + 263 days. ACOG recommends dating IVF pregnancies this way because the embryo's age and transfer date are known exactly.
Our due date calculator has an IVF option. Below are the formulas, worked examples and answers for frozen transfers.
Why IVF due dates are calculated differently
Most pregnancies are dated from the first day of the last menstrual period (LMP), because the day of conception isn't known. With IVF, it is. Your clinic knows when the eggs were fertilised and how many days the embryo grew before transfer.
ACOG Committee Opinion No. 700 recommends that if a pregnancy resulted from assisted reproductive technology, the ART-derived gestational age should be used for the due date. For IVF, that means using the embryo's age and the date of transfer.
To keep IVF pregnancies on the same scale as everyone else's (so "12 weeks" means the same thing on every scan and chart), the calculation creates an equivalent LMP date two weeks before fertilisation.
IVF due date formulas
General formula: due date = transfer date + (266 − embryo age in days)
| Embryo age at transfer | Add to transfer date | Gestational age on transfer day | Equivalent LMP |
|---|---|---|---|
| Day 3 (cleavage stage) | 263 days | 2 weeks 3 days | 17 days before transfer |
| Day 5 (blastocyst) | 261 days | 2 weeks 5 days | 19 days before transfer |
| Day 6 (blastocyst) | 260 days | 2 weeks 6 days | 20 days before transfer |
| Egg retrieval / fertilisation date (day 0) | 266 days from retrieval | 2 weeks on retrieval day | 14 days before retrieval |
Why 266? It's the average 38 weeks from fertilisation to birth, which is 280 days from LMP minus the 14 days before ovulation.
Worked examples
Day 5 transfer
- Blastocyst transferred on 4 May 2026
- Due date = 4 May 2026 + 261 days = 20 January 2027
- Equivalent LMP: 15 April 2026
- On 20 October 2026 you would be 26 weeks 6 days pregnant
Day 3 transfer
- Embryo transferred on 4 May 2026
- Due date = 4 May 2026 + 263 days = 22 January 2027
Frozen embryo transfer (FET)
- Day-5 embryo frozen in 2025, thawed and transferred on 17 August 2026
- Due date = 17 August 2026 + 261 days = 5 May 2027
- Equivalent LMP: 29 July 2026
The time an embryo spends frozen doesn't count. Only its developmental age at freezing (day 5 here) and the transfer date matter.
From egg retrieval
- Eggs retrieved and fertilised on 2 March 2026, fresh transfer a few days later
- Due date = 2 March 2026 + 266 days = 23 November 2026
Retrieval-based and transfer-based dates match, because both count from fertilisation.
How many weeks pregnant am I after embryo transfer?
Add two weeks plus the embryo's age to the days since transfer:
gestational age = days since transfer + 14 + embryo age
So 10 days after a day-5 transfer, you're 10 + 14 + 5 = 29 days, or 4 weeks 1 day pregnant. This is why clinics often schedule the first pregnancy blood test around 9 to 14 days after transfer, when you're about 4 weeks pregnant. Check your clinic's instructions, as timing varies.
Once you have your due date, How Many Weeks Pregnant Am I? will show your current week, and the pregnancy week by week guide shows what's happening each week.
Other fertility treatments
- Donor eggs or embryos: same method. Use the transfer date and embryo age.
- IUI (intrauterine insemination): the insemination usually happens around ovulation, so many providers add 266 days to the insemination or ovulation date, or date the pregnancy by an early scan. Our guide to the due date calculator from conception explains the ovulation-based method.
- Ovulation induction with timed intercourse: dated from LMP, ovulation or an early scan, as your provider decides.
For an overview of treatments, see ACOG's patient guide to treating infertility.
Will my IVF due date change?
Usually not. ACOG says changes to an established due date should be reserved for rare circumstances, and for IVF pregnancies the transfer-based date is the reference. Your clinic or obstetric provider may still measure your baby at early scans to check growth, but that's not the same as re-dating the pregnancy.
Use your clinic's date. If your fertility clinic gives you a slightly different due date, for example because they count from retrieval or use a different day convention, follow theirs and tell your obstetric provider which date they gave you.
Twins and multiple pregnancy
The due date for twins from IVF is calculated in exactly the same way. Twin pregnancies are more likely to be born early, and your care team will usually plan extra scans and talk with you about the timing of birth. Track the official due date, and keep your appointment schedule handy. See our pregnancy appointment schedule for the typical visits.
Track your IVF pregnancy in Momi
After an IVF journey, many parents want to record every step. Momi follows your pregnancy week by week once your due date is set, and gives you a place for scan pictures, appointments and medicine reminders (useful if you're on progesterone or other prescribed medicines), a pregnancy diary and a weekly bump photo journal. Enter the due date your clinic gives you.
Download Momi free on the App Store or Google Play. Free with ads; optional Premium.
Sources
- ACOG Committee Opinion No. 700, Methods for Estimating the Due Date
- ACOG, Treating Infertility
- NHS, Due date calculator
Medical disclaimer: Momi and this website provide general information, not medical advice. Always talk to your doctor or midwife; in an emergency call your local emergency number.
FAQ
How do you calculate an IVF due date?
Add 266 days to the date of egg retrieval or fertilisation, or add 266 days minus the embryo's age to your transfer date. That means transfer date plus 263 days for a day-3 embryo, 261 days for a day-5 embryo and 260 days for a day-6 embryo.
What is my due date after a 5-day transfer?
Add 261 days to your transfer date. For example, a day-5 blastocyst transferred on 4 May 2026 gives an estimated due date of 20 January 2027. On transfer day you count as 2 weeks and 5 days pregnant.
Is the due date different for a frozen embryo transfer?
The method is the same. Use the date of the frozen embryo transfer and the age the embryo was when it was frozen, usually day 5 or 6. The time it spent frozen doesn't count.
How many weeks pregnant am I after embryo transfer?
On the day of transfer you're 2 weeks plus the embryo's age: 2 weeks 3 days for a day-3 embryo, 2 weeks 5 days for a day-5 embryo. Add the days since transfer to get your current gestational age.
Will my IVF due date change after an ultrasound?
Usually not. ACOG recommends that IVF pregnancies be dated from the embryo's age and transfer date, because the timing is known precisely. Your provider may still note scan measurements, but changes to the due date should be rare.
Does IVF with twins change the due date?
The estimated due date is calculated the same way. Twin pregnancies are more likely to be born before the due date, and your care team will plan monitoring and timing of birth with you.
Related guides
Track this in Momi
Momi is a free pregnancy tracker app for iPhone and Android that follows pregnancy week by week, estimates the due date, and keeps a pregnancy journal, weight log, kick counter and contraction timer in one place.
