Ovulation Calculator

Ovulation typically occurs 14 days before your next period — not 14 days after the start of your last period. This distinction matters for women with irregular cycles. With a 28-day cycle, ovulation is around day 14. With a 32-day cycle, it shifts to approximately day 18. The fertile window spans about 6 days: the 5 days before ovulation (sperm can survive up to 5 days in the reproductive tract) plus the day of ovulation itself (the egg survives 12-24 hours after release). The highest probability of conception is the day before and the day of ovulation, with approximately a 25-30% chance per cycle for healthy couples timing intercourse correctly. This calculator estimates your ovulation date and fertile window based on your average cycle length and last period start date. For women with regular cycles (21-35 days with less than 7 days variation), calendar-based prediction is reasonably accurate. All calculations use standard reproductive biology formulas and run entirely in your browser.

Several factors can shift ovulation timing within a cycle. Stress — both physical and emotional — can delay ovulation by days or even weeks through its effect on GnRH (gonadotropin-releasing hormone) production. Illness, travel across time zones, significant weight changes (gaining or losing 5%+ of body weight), and intense exercise can all affect cycle regularity. Certain medications, including some antidepressants and anti-inflammatory drugs, may also influence ovulation timing. For more precise tracking, many women combine calendar calculations with other fertility awareness methods: basal body temperature (BBT rises 0.2-0.5°C after ovulation), cervical mucus changes (becomes clear and stretchy like egg whites near ovulation), and ovulation predictor kits (detect the LH surge 24-36 hours before ovulation). This calculator provides the calendar-based estimate as a starting point. For conception planning or natural family planning, combining multiple methods improves accuracy. No personal health data leaves your browser.