Due Date Calculator

An IVF transfer date, because the embryo’s age is known exactly. Otherwise an ultrasound in the first trimester: the American College of Obstetricians and Gynecologists (ACOG) treats a measurement up to 13 weeks 6 days as the most accurate way to set or confirm the due date, and clinicians change a date based on the last period when the two disagree by more than a set margin.

Because the first day of the last period is a date most people know, while the day of conception usually is not. Week 0 therefore starts about two weeks before conception, and a pregnancy conceived on 15 March is already two weeks along that day. The conception, IVF and ultrasound methods are converted to the same clock, which is why the page shows the last-period date each due date implies.

From the transfer date and the embryo’s age. A day-5 blastocyst is treated as a pregnancy of 2 weeks and 5 days on the day of transfer, so the due date is 261 days later; a day-3 embryo gives 263 days. These are the offsets ACOG gives, and a frozen embryo transfer is dated the same way, from the day of the transfer.

Only around 4%. A due date is the middle of a normal range rather than an appointment: a birth from 37 weeks on counts as term, and most babies arrive within two weeks either side of the date. The milestones table shows when each stretch begins.

They are ACOG’s labels for births in the term window: early term from 37 weeks 0 days to 38 weeks 6 days, full term from 39+0 to 40+6, late term from 41+0 to 41+6, and post-term from 42 weeks on. A baby born before 37 weeks is preterm.