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Ovulation & Fertility Calculator
Estimate your fertile window each cycle.
An estimate based on cycle averages. Actual ovulation varies — this is not a substitute for medical advice or contraception.
Enter your last period and cycle length.
About the Ovulation Calculator
Free ovulation calculator. Enter the first day of your last period and your cycle length to estimate your fertile window, ovulation day and next period.
Everything is calculated instantly in your browser — nothing you type is uploaded or stored. Bookmark Calcooly for the next time you need it.