Due Date Calculator
The same math your provider does at your first visit — in three flavors. Save your date and the whole site counts down with you.
21-45 days · use 28 if unsure
If you tracked ovulation, conception is ovulation day (or 1-2 days after).
Only an estimate — about 4 in 5 babies arrive within a week of their due date, not on it. Your provider may adjust the date after a first-trimester ultrasound, and that dating comes first.
How this calculator works
Last period method: Naegele's rule adds 280 days (40 weeks) to the first day of your last period. If your cycles run longer or shorter than 28 days, we shift the result by the difference, because ovulation — and conception — happen about 14 days before the next period, whenever that falls.
Conception method: the average pregnancy lasts 266 days from conception.
IVF method: embryos are already "old" at transfer, so we count 266 days minus the embryo's age (261 days after a day-5 blastocyst transfer, 263 after a day-3 transfer). IVF dating is the most precise of the three.
Questions people ask
Which method is most accurate?
IVF transfer dating, because the moment of conception is known exactly. Next comes dating from a first-trimester ultrasound. LMP-based estimates are good starting points but assume a 28-day cycle with mid-cycle ovulation.
Can my due date change?
Yes — if a first-trimester ultrasound suggests a different age, providers often revise the date. Later ultrasounds rarely change it, because babies then grow at naturally different rates.
What if my cycle is irregular?
Ultrasound dating will serve you better than any calculator. In the meantime, an early positive test and ovulation tracking can help your provider narrow the window.