Ovulation Calculator
Estimate your fertile window from your last period and cycle length.
Enter values
days
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The formula
ovulation ≈ (last period + cycle length) − 14 days
All calculations run locally in your browser and update instantly as you type.
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Frequently asked questions
How accurate is this?+
It is an estimate based on a regular cycle. Real ovulation shifts with cycle variation, stress and health, so treat it as a guide, not a medical certainty.
All calculations run locally in your browser. Nothing you type is sent to a server.