Ovulation Calculator
Find your estimated ovulation date and fertile window from your last period and average cycle length.
100% client-side · no upload
Estimated Ovulation Date
Fertile Window
Next Period Expected
How to use
- Enter the first day of your last menstrual period.
- Enter your average cycle length (default is 28 days).
- Click Calculate Ovulation to see your ovulation date, fertile window, and next period estimate.
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常見問題
- Is this ovulation calculator free?
- Yes, completely free with no signup and no usage limits.
- Does my data leave my device?
- No. All calculations run in JavaScript inside your browser. Nothing is sent to any server.
- Does it work on mobile?
- Yes. The calculator is mobile-first and works on iPhone Safari and Android Chrome.