Your cycle phases
Bands show menstrual, follicular, fertile, and luteal phases. The pointer is today.
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Ovulation Calculator
Estimate your most fertile days, your ovulation date, and your next period from the start of your last period and your average cycle length.
Most fertile window
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Ovulation day—
Next period—
Estimated due date if pregnant—
How it works
Ovulation happens about 14 days before your next period starts — the luteal phase is fairly constant even when cycle length varies. Your fertile window spans the five days before ovulation plus ovulation day itself, because sperm can survive up to five days while the egg lasts about 24 hours.
Ovulation = LMP + (cycle length − 14)
Fertile window = ovulation − 5 days … ovulation + 1 day
Next period = LMP + cycle length
Fertile window = ovulation − 5 days … ovulation + 1 day
Next period = LMP + cycle length
Frequently asked questions
When are the best days to conceive?
The two days before ovulation and ovulation day itself are the most fertile. Regular intercourse across the fertile window gives the best odds.
How accurate is calendar-based ovulation?
It is a good estimate for regular cycles but less reliable if your cycle varies. Ovulation predictor kits or basal body temperature tracking add precision.