For fresh and frozen (FET) transfers — enter your transfer date and embryo age to get a due date estimate based on your actual timeline, not a guessed ovulation day.
Unlike a natural pregnancy, IVF gives us a known, exact "conception-equivalent" date — the transfer date minus the embryo's age. From there, the same 266-day rule applies:
Want to work backward from a due date instead? Try the Reverse Due Date Calculator.
It's based on your embryo transfer date minus the embryo's age (3, 5 or 6 days), which gives an equivalent conception date. Adding 266 days to that date gives the estimated due date — the same method fertility clinics use.
A Day 3 embryo (cleavage stage) is transferred earlier in its development than a Day 5 embryo (blastocyst stage). Because a Day 5 embryo is 2 days more developed at transfer, fewer days need to be added afterward to reach the same 266-day conception-equivalent point.
A Day 6 transfer follows the same logic as Day 5, just one day later in embryo development — so one day fewer is added after the transfer date to reach the estimated due date.
Generally yes, because it's based on a known, exact transfer date rather than an assumed ovulation day estimated from your last period. That said, your fertility clinic's estimate, which may also factor in early ultrasound measurements, is the most reliable source.