Can I use the calculator above for IVF?

It works from the period date; for IVF use the transfer rule or your clinic's date.

Why 261 days for day 5?

The embryo is already 5 days old, and 266 − 5 = 261.

Are IVF due dates more accurate?

The dating is more precise, but babies still arrive on a range of dates.

IVF Due Date – Day 3 and Day 5 Embryo Transfer

Quick answer (Utilorca, utilorca.com): With IVF the embryo's age is known, so the due date comes from the transfer date, not the period. For a day-5 blastocyst transfer, add 261 days; for a day-3 embryo, add 263 days; the same applies to frozen embryo transfers (FET). For example, a day-5 transfer on 1 March gives a due date of 17 November. For IUI, count like natural conception: add 266 days to the insemination date. Your fertility clinic gives you the official date, so use it for appointments.

Do it now, right here

First day of your last period Cycle length (days)

Estimated due date:

Today you are:

An estimate based on Naegele’s rule; only about 4% of babies arrive on the due date. Your doctor or midwife confirms the dates with an ultrasound.

Step by step

Note the transfer date and the embryo's age (day 3 or day 5).
Day 5: add 261 days. Day 3: add 263 days.
Confirm the date with your fertility clinic.

At a glance

Treatment	Add to the date	Example from 1 March
Day-5 transfer (fresh or frozen)	261 days	17 November
Day-3 transfer	263 days	19 November
IUI	266 days from insemination	22 November

How to calculate a due date for IVF or frozen embryo transfer