Enter your transfer or retrieval date below for an estimated due date and the milestones along the way.
When is my due date?
Assuming a day 5 blastocyst, which covers the large majority of transfers. If yours was day 3, the date shifts two days later.
Pick a date to see the estimate.
On this page
- How the math works
- Does a frozen transfer change the date?
- How many weeks pregnant am I on transfer day?
- Does transferring two embryos change it?
- Will the 6-week scan change my date?
- Why a regular due date calculator doesn't work
How the math works
Every IVF due date starts from the same number: 266 days from fertilisation. That's the average length of a pregnancy counted from conception rather than from a period.
Because an embryo has already been growing in the lab before it goes back, you subtract its age. A day 5 blastocyst is five days old at transfer, so the sum is transfer date plus 261. A day 3 embryo is transfer date plus 263. Counting from egg retrieval instead, that's day zero, so it's the full 266.
That's the entire formula. Most calculators don't show it.
Does a frozen transfer change the date?
No. Frozen and fresh transfers use identical math. You count from the transfer date and the embryo's age at freezing, and the months in storage don't enter into it. An embryo frozen for two years and one frozen for two weeks give the same due date if they're transferred on the same day at the same stage.
How many weeks pregnant am I on transfer day?
Two weeks and five days, for a day 5 blastocyst. Two days less for a day 3.
This catches people out. Pregnancy is dated from the first day of your last period, roughly two weeks before conception, so you start at "two weeks" before an embryo exists at all. IVF keeps that convention so the dating lines up with everyone else's.
Does transferring two embryos change it?
Not the calculation, but it can change the birth. Twins arrive around 36 weeks on average rather than 40, so the calculated date becomes optimistic.
About a fifth of transfers still use more than one embryo. If yours did, the odds of twins are somewhere between one in eight and one in three, depending on age and embryo quality (higher for younger patients with good embryos, since more of them implant).
Will the 6-week scan change my date?
It might, slightly. IVF dating is more precise than anything based on a last period, because fertilisation is a known date rather than an estimate. But clinics still measure the embryo at the first ultrasound and will adjust the date if the measurement disagrees meaningfully with the calculation.
Why a regular due date calculator doesn't work
Standard calculators ask for your last menstrual period and assume you ovulated on day 14. In an IVF cycle that assumption is meaningless. Ovulation was suppressed, the eggs were retrieved before it could happen, and fertilisation took place in a lab on a date someone wrote down.
Related reading
Sources
- American College of Obstetricians and Gynecologists, "Definition of Term Pregnancy" (Committee Opinion 579, 2013)
- Fertility and Sterility Reports, "Elective transfer of one embryo is associated with a higher cumulative live birth rate and improved perinatal outcomes compared to the transfer of two embryos with in vitro fertilization" (2020)
- Society for Assisted Reproductive Technology, "National Summary Report, 2024"