HEALTH TOOL
Ovulation Calculator
Estimate ovulation day and fertile window from your last period.
Estimated ovulation day
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Fertile window
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Next period expected
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About this tool
Estimate your most fertile days based on the first day of your last period and your average cycle length. This is a general statistical estimate, not a substitute for medical or fertility-tracking advice — actual ovulation timing varies cycle to cycle.
Frequently asked questions
- How is ovulation day calculated?
- Ovulation typically occurs about 14 days before the next period starts, regardless of cycle length — so this is estimated as cycle length minus 14 days after your last period began.
- What is the "fertile window"?
- The five days leading up to and including estimated ovulation, when pregnancy is most likely, based on typical sperm survival time and egg viability.
- How accurate is this for irregular cycles?
- Less accurate — this estimate assumes a fairly regular cycle. For irregular cycles, dedicated ovulation tracking methods (basal body temperature, ovulation predictor kits) are more reliable.