Fertility Calculator

Ovulation is calculated by subtracting your luteal phase length from your total cycle length. For a 28-day cycle with a 14-day luteal phase, ovulation occurs on day 14. The formula is: Ovulation Day = Cycle Length - Luteal Phase Length. This method assumes the luteal phase is relatively consistent from cycle to cycle.

The fertile window spans about 6 days: the 5 days before ovulation and the day of ovulation itself. Sperm can survive in the female reproductive tract for up to 5 days, while an egg is viable for only 12-24 hours after release. Having intercourse during this window maximizes the chance of conception.

A normal menstrual cycle ranges from 21 to 35 days, with 28 days being the average. Cycle length is counted from the first day of one period to the first day of the next. Variations of a few days are common and normal. If your cycles are consistently outside this range, consult a healthcare provider.

The calendar method is most accurate for women with regular cycles. Factors like stress, illness, travel, and hormonal changes can affect ovulation timing. For best results, combine this calculator with basal body temperature (BBT) tracking, ovulation predictor kits (OPKs), or cervical mucus monitoring.

The luteal phase is the time between ovulation and the start of your next period. It typically lasts 10-16 days and remains relatively consistent for most women. A luteal phase shorter than 10 days may indicate a luteal phase defect, which can affect fertility. If you do not know your luteal phase length, 14 days is a reasonable default.