👶 Due Date Calculator
Estimate your baby's due date using your last period, conception date, or IVF embryo transfer date.
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Due dates are estimates. Only about 5% of babies are born on their exact due date. IVF calculations here assume a standard 266-day gestation from ovulation, adjusted for transfer day — confirm exact dating with your fertility clinic.
How the Due Date Calculator Works
There are several accepted ways to estimate a due date, depending on what information you have available.
Formula
From conception date: Due date = Conception date + 266 days
From IVF Day 5 transfer: Due date = Transfer date + 261 days
From IVF Day 3 transfer: Due date = Transfer date + 263 days
Why IVF Dating Differs
With IVF, the embryo's age at transfer is known precisely, so the calculation starts from the transfer date rather than an estimated ovulation date. A Day 5 (blastocyst) transfer embryo is 5 days past conception, and a Day 3 embryo is 3 days past conception, so fewer days are added to reach the standard 266-day post-conception due date.
Frequently Asked Questions
Which method is most accurate?
IVF transfer dating is typically the most precise since the exact embryo age is known. Ultrasound dating in the first trimester is also highly accurate. LMP-based dating is the most common but assumes a regular cycle.
Why is 280 days used from the last period?
Pregnancy is conventionally dated as 40 weeks (280 days) from the first day of the last menstrual period, even though conception typically occurs about two weeks later.
Can my due date change?
Yes. Due dates are commonly adjusted after an early ultrasound, which can more precisely measure fetal size and gestational age.