Pregnancy Due Date Calculator
Choose your calculation method and enter the relevant date to estimate your due date.
Last updated: September 5, 2026
Frequently asked questions
How is a due date calculated from the last menstrual period (LMP)?
Add 280 days (40 weeks) to the first day of your last period - this is Naegele's rule, the standard method, which assumes a 28-day cycle with ovulation on day 14. It's an estimate; actual cycle length affects real conception timing.
How is an IVF due date different from an LMP-based due date?
IVF due dates are calculated from a known transfer date rather than an estimated ovulation date, which makes them more precise. A day-5 (blastocyst) transfer adds 261 days to the transfer date, and a day-3 transfer adds 263 days - both account for the embryo's exact age at transfer.
How accurate are due date estimates?
Only about 5% of babies are born on their exact estimated due date - most arrive within a 2-week window before or after. Due dates are a statistical estimate of a full-term timeline, not a precise prediction, and your care provider's ultrasound-based dating is generally more reliable than a calculation from LMP alone.
Is an 'ivf birth date calculator' the same as this tool?
Yes - select "IVF transfer" as the calculation method above (day 3 or day 5, depending on your embryo's transfer stage) to get an IVF-specific due date estimate.
What's an example due date calculation from LMP?
If the first day of your last period was January 1st, adding 280 days (Naegele's rule) puts your estimated due date around October 8th.
How is a due date calculated from a known conception date instead of LMP?
From a known conception date, add 266 days (38 weeks) rather than 280 days, since conception typically occurs about two weeks after the start of the last period - this shifts the estimate compared to the LMP method by roughly that same two-week gap.
Can this due date change later in pregnancy?
Yes - an early ultrasound (typically in the first trimester) is generally considered more accurate than an LMP-based estimate and may shift your official due date by several days if your cycle wasn't exactly 28 days or ovulation timing differed from the standard assumption.