How the dates are calculated
| Transfer type | Due date | Equivalent LMP |
|---|---|---|
| Day-3 embryo transfer | transfer + 263 days | transfer − 17 days |
| Day-5 (blastocyst) transfer | transfer + 261 days | transfer − 19 days |
| Day-6 (blastocyst) transfer | transfer + 260 days | transfer − 20 days |
Logic: a pregnancy is 266 days from fertilization, and the embryo was already 3, 5 or 6 days old at transfer — so EDD = transfer + (266 − embryo age). The equivalent LMP places fertilization on "cycle day 14", which lets standard 40-week dating work as usual.
OB wheel for clinicians: IVF transfer dating (day-3, day-5, day-6), ACOG ultrasound redating and the Bishop score. The wheel keeps a visible note that dates came from IVF. No account, no patient data stored, works offline.
Get Partus on the App StoreCommon questions
Why does the transfer day change the due date?
Because the embryo's age is known exactly. A day-5 embryo is two days further along than a day-3 embryo, so the due date lands two days earlier relative to the same transfer date.
Does this work for frozen embryo transfers (FET)?
Yes. What matters is the embryo's developmental age at transfer, not whether it was fresh or frozen. A thawed day-5 blastocyst is dated as day-5.
What about day-6 or day-7 blastocysts?
Day-6 transfers use transfer + 260 days — most calculators skip this option. Day-7 transfers (rare) would follow the same logic at + 259 days; confirm dating with the treating fertility clinic.
Why is IVF dating more accurate than LMP dating?
The fertilization date is known to the day, so there is no recall error and no cycle-length assumption. ACOG treats IVF-derived dating as the most reliable method available.
Can an ultrasound change an IVF due date?
IVF dating is generally kept, because it is more precise than measurement-based estimates. For non-IVF pregnancies, ultrasound may replace LMP dating — check our ACOG redating calculator.
Source
Methods for Estimating the Due Date. ACOG Committee Opinion No. 700, May 2017 (age-of-embryo method for ART pregnancies). This page is a reference tool for healthcare professionals. It does not provide medical advice or diagnosis.