Ovulation Calculator
Estimate your ovulation day, fertile window and next period from your last period — simple, private and free.
Ovulation Day
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Fertile Window
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Next Period
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This is an estimate for information only — not medical advice, and not a contraception method. Cycles vary; confirm important decisions with your doctor.
How to use
- Enter the first day of your last period.
- Slide the cycle length to your usual cycle (21–35 days) and set period length.
- See your ovulation day, fertile window and next period instantly.
Frequently Asked Questions (FAQ)
What does the ovulation calculator estimate?
Your ovulation day, fertile window and next period, from the first day of your last period, your period length and your cycle length.
What cycle lengths does it support?
Cycle lengths from 21 to 35 days, set with a slider.
Is the fertile window exact?
No. It is an estimate based on average cycle timing, and actual ovulation can shift from cycle to cycle.
Can I use it as a contraception method?
No. It is an estimate for information only, not a contraception method. Confirm important decisions with your doctor.
Is my information kept private?
Yes. All calculations run locally in your browser, so no data is sent anywhere.