How IVF and FET due dates work
With a standard pregnancy, the due date is calculated by adding 280 days to the first day of the last menstrual period - a formula that bakes in an assumed 14-day follicular phase. IVF removes that assumption entirely because fertilization happens in the lab on a known date.
The formula is: due date = transfer date + (280 - 14 - embryo age). For a Day-5 blastocyst that means +261 days. For a Day-3 embryo it means +263 days - two days longer because the embryo is two days younger at transfer.
Transfer day vs frozen transfer
A frozen embryo transfer (FET) uses exactly the same calculation - what matters is the age of the embryo on the day it was transferred, not whether it spent time cryopreserved. Most frozen transfers use Day-5 blastocysts, so the Day-5 setting is the right choice for most FET cycles.
If you conceived naturally or via intrauterine insemination (IUI), use the standard due date calculator instead. Once you have your estimated due date from an IVF transfer, you can confirm it against your first ultrasound using the ultrasound due date calculator.
Frequently asked questions
How is an IVF due date calculated?
Because the embryo's age at transfer is known, we count forward from the transfer date: a Day-5 blastocyst due date is the transfer date plus 261 days, and a Day-3 transfer is the transfer date plus 263 days. This is equivalent to a 280-day pregnancy counted from a known ovulation.
Is an FET due date different?
No. A frozen embryo transfer uses the same math - what matters is the age of the embryo when it was transferred, not that it was frozen. A thawed Day-5 blastocyst uses the Day-5 calculation.
Why is an IVF due date more accurate?
Standard due dates assume ovulation on day 14 of a 28-day cycle, which is just an average. With IVF the fertilization date is known to the day, so there is no guesswork about when conception happened.
These calculators give estimates based on cycle averages and standard formulas. They are for general information only and are not medical advice. For anything concerning your health or pregnancy, talk to a qualified healthcare provider.