How the IVF due date calculator works
Why IVF dating is different
Standard dating estimates ovulation backward from a period; IVF knows the embryo's exact age — a 5-day blastocyst is 5 days old at transfer. The due date is therefore transfer date + 261 days (5-day) or + 263 (3-day), accurate to the day with no statistical rounding. It is the one pregnancy dating method with no error bars worth mentioning.
The equivalent-LMP trick
Every chart, app, and week counter runs on LMP-based gestational age. The bridge: a 5-day transfer has an "equivalent LMP" 19 days before transfer (2 weeks + 5 days of pre-existing development). The calculator computes it so standard week counters stay aligned with your clinic's dating.
Frozen transfers and the same math
Frozen embryo transfers date identically — the embryo's developmental age is what counts, not its storage history. A frozen 5-day transfer dates exactly like a fresh one. Donor eggs, surrogacy timelines, and repeated transfers all run the same single formula: transfer date + embryo age offset.