Fertile Window Calculator

The fertile window is the approximately 6-day period during each menstrual cycle when pregnancy is possible: the 5 days before ovulation and the day of ovulation. Sperm can survive up to 5 days in the reproductive tract, but the egg lives only 12-24 hours.

The highest probability of conception is on the 2 days before ovulation and ovulation day itself. These 3 days account for the vast majority of pregnancies. The probability drops significantly on the other days of the fertile window.

For women with regular 28-day cycles, predictions are reasonably accurate. For irregular cycles, accuracy decreases. Combining this calculator with ovulation predictor kits (OPKs) or basal body temperature tracking provides the most reliable results.