Conception Date Calculator

Choose whether you know the due date or the first day of your last period, and enter it (and your usual cycle length). The calculator gives the most likely conception date and the fertile window around it.

Ovulation usually occurs about 14 days before the next period, so in a 28-day cycle it's around day 14. Conception happens within about a day of ovulation, but sperm can survive for up to 5 days, so the intercourse that led to pregnancy may have been several days earlier.

Conception ≈ due date − 266 days ≈ LMP + (cycle length − 14) days

266

average days from conception to birth

LMP

first day of the last menstrual period

• An estimate of a window, not an exact date: cycles and ovulation vary, and due dates themselves are estimates.