Fertile Window Calculator

1. Enter the first day of your last period.
2. Enter your average cycle length, from the first day of one period to the first day of the next.
3. See your next fertile window, estimated ovulation date, and forecast for the next 3 cycles.

Ovulation usually occurs about 14 days before your next period (the typical length of the luteal phase). Since sperm can survive for up to 5 days and an egg for about 1 day, the fertile window runs from 5 days before ovulation through 1 day afterward. In a 28-day cycle, ovulation typically occurs around day 14.

Calendar-based calculations work best for regular cycles and are only estimates. Stress, illness, the postpartum period, breastfeeding, hormones, and natural cycle variations can all affect ovulation timing. Your data stays in your browser.

This is not a contraceptive method. The calendar method has a high failure rate with typical use. Choose a birth control method with guidance from a healthcare professional. References: the World Health Organization and public health guidance on sexual and reproductive health. This calculator is for informational purposes only and does not replace a consultation, tests, or care from a healthcare professional.