Due Date & Test Date Planner

A pregnancy is counted as 40 weeks (280 days) from the first day of the last period, and ovulation or fertilization is assumed to fall about 14 days into that count. With IVF the embryo’s age is known, so ACOG’s guidance is to date from the transfer.

Due date = transfer date + 266 days − embryo age

ACOG Committee Opinion 700 gives two examples: +261 days for a day-5 embryo and +263 days for a day-3 embryo. A fresh day-5 embryo grown out and transferred on day 6 is +260.

Frozen blastocysts are dated as day 5. Whether a blastocyst was frozen on day 5, 6 or 7 only reflects how fast it reached the blastocyst stage. A frozen transfer is timed to the uterine lining, not to the day of freezing, so every frozen blastocyst uses +261. Some practices instead date a day-6 frozen blastocyst by its freezing day (+260, or +259 for day 7); the difference is one or two days and the first-trimester ultrasound settles it. A frozen day-3 embryo uses +263.

Due date = last period + 280 days + (your cycle length − 28)

This is Naëgele’s rule with the usual cycle-length adjustment. If you know the conception date instead, the due date is that date + 266 days (38 weeks).

If you have a first-trimester ultrasound, ACOG says that measurement is the most accurate way to confirm the date, and your doctor may adjust it.

Due date = insemination date + 266 days

Insemination is treated as conception, which sits 38 weeks (266 days) before delivery on the standard 40-week count. The “equivalent last period” is the IUI date minus 14 days.