Ovulation Calculator
Estimate your ovulation date, fertile window, and next period based on your cycle.
Ovulation and fertility — how the calculation works
Ovulation typically occurs about 14 days before your next period begins. This is called the luteal phase, and it is relatively consistent at around 14 days for most people, even when total cycle length varies.
The fertile window spans approximately 6 days: the 5 days leading up to ovulation and the day of ovulation itself. Sperm can survive in the reproductive tract for up to 5 days, while the released egg is viable for only 12 to 24 hours.
- Cycle length matters: A 28-day cycle means ovulation around day 14. A 32-day cycle means ovulation around day 18. The key is subtracting 14 from your total cycle length.
- Irregular cycles: If your cycles vary by more than a few days, calendar-based predictions become less reliable. Consider combining this method with ovulation predictor kits (OPKs) or basal body temperature tracking.
- Peak fertility: The two days before ovulation and the day of ovulation itself are when conception is most likely. Studies suggest intercourse on these days yields the highest pregnancy rates.
- Signs of ovulation: Some people experience mild pelvic pain (mittelschmerz), changes in cervical mucus (clear and stretchy), or a slight rise in basal body temperature after ovulation.
Frequently Asked Questions
When do I ovulate?
Ovulation typically occurs about 14 days before your next period. For a 28-day cycle, that's around day 14. For longer or shorter cycles, subtract 14 from your total cycle length to estimate the ovulation day.
How long is the fertile window?
The fertile window is approximately 6 days long — the 5 days before ovulation plus the day of ovulation itself. Sperm can survive in the reproductive tract for up to 5 days, while the egg is viable for about 12–24 hours after release.
Can I get pregnant outside my fertile window?
It is very unlikely to conceive outside the fertile window. However, cycles can be irregular, and ovulation timing can shift due to stress, illness, or hormonal changes, so the actual fertile window may differ from predictions.
How accurate are ovulation calculators?
Ovulation calculators provide estimates based on average cycle patterns. They work best for people with regular cycles. For greater accuracy, combine calendar tracking with ovulation predictor kits (OPKs), basal body temperature charting, or cervical mucus monitoring.