Find out when conception likely occurred based on your last menstrual period or your due date, along with the probable conception window.
Conception usually occurs around ovulation, which takes place approximately 14 days after the first day of the last menstrual period for a standard 28-day cycle. If your cycle length differs, ovulation shifts accordingly — one day earlier or later for each day the cycle deviates from 28.
The conception window spans roughly 6 days ending on ovulation day — the 5 days before ovulation plus ovulation itself — because sperm can survive up to 5 days in the reproductive tract.
Note: Only a DNA test can definitively confirm paternity or exact conception timing. This calculator provides statistical estimates for informational purposes.