Ovulation
Calculate ovulation date and fertile window
These calculators provide general information only and are not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider.
How to use Ovulation
- 1Enter first day of last period and average cycle length (default 28).
- 2The tool estimates ovulation (~14 days before next period) and the fertile window.
- 3See estimated ovulation for the next 6 cycles to plan or avoid.
How to find ovulation: cycle and ovulation day
ovulation ≈ next period − 14 days; fertile ≈ 5 days before to 1 day afterOvulation usually happens ~14 days before the next period (luteal phase is fairly fixed), while follicular length varies, so 'cycle−14' beats 'cycle÷2'.
Sperm survive ~3–5 days, egg ~12–24 h, so the fertile window spans ~5 days before to 1 day after ovulation—about a week.
Good for regular cycles as an estimate; for precision use basal temperature, OPKs, or an app. Irregular cycles widen the error.
Frequently asked questions
Can I calculate with irregular cycles?
You can estimate but with larger error. The more variable the cycle, the harder ovulation is to predict—verify with OPK + temperature.
Why is the fertile window so long?
Sperm live for days and ovulation can shift, so covering the days around ovulation is safest.
Used for both trying and avoiding?
Yes, same principle: time intercourse for conception, or use protection to avoid—ovulation tracking alone isn't reliable birth control.