Ovulation Calculator

This ovulation calculator estimates when you ovulate based on your last menstrual period (LMP) and cycle length. Ovulation typically occurs approximately 14 days before the start of the next period — which means for a 28-day cycle it falls on day 14, but for a 32-day cycle it falls on day 18. The fertile window spans five days before ovulation through one day after, because sperm can survive in the fallopian tubes for up to five days, and the egg is viable for 12–24 hours after release. These are statistical averages — actual ovulation timing varies cycle to cycle and is influenced by stress, illness, travel, and hormonal fluctuations. For the most accurate ovulation detection, use basal body temperature (BBT) charting, cervical mucus monitoring, or a LH surge ovulation predictor kit (OPK). This calculator is for general education only and should not be used as a contraceptive method.

Ovulation timing is estimated using the luteal phase constant: ovulation occurs approximately 14 days before the start of the next period. For any cycle length, ovulation day = cycle length − 14. For a 28-day cycle, ovulation is on day 14. For a 32-day cycle, it is on day 18. The fertile window runs from 5 days before ovulation through 1 day after — this accounts for sperm lifespan (up to 5 days in fertile cervical mucus) and egg viability (12–24 hours post-ovulation). Current cycle day = days since the first day of your last period. Days until ovulation = ovulation day − current cycle day. If that number is negative, you are past ovulation in the current cycle and the calculator shows days until next cycle's ovulation. These are statistical estimates based on average cycle patterns; actual ovulation varies. For reliable detection, use LH ovulation predictor kits or basal body temperature charting.