Period & Ovulation Calculator
Predict your next period, ovulation day, and fertile window
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🔒 Everything runs 100% in your browser. Your files and input are never uploaded to any server.
Enter your last period start date along with your average cycle and period length, and this tool instantly predicts your next three period dates, ovulation days, and fertile windows. It's handy for anyone tracking their cycle or planning for pregnancy, and since every calculation runs right in your browser, none of your dates are ever sent to a server.
How to use
- Pick your last period start date using the date field.
- Enter your average cycle length (21-45 days) and period length (3-10 days).
- Check the top panel for the nearest upcoming period start date, ovulation day, and fertile window.
- Scroll down to see the schedule for the next 3 cycles.
FAQ
- How is ovulation day calculated?
- Ovulation is estimated as 14 days before your next expected period, and the fertile window spans from 5 days before to 1 day after that date.
- Are the results guaranteed to be accurate?
- This is a prediction based on average cycle math, not a medical diagnosis. Actual ovulation and periods can vary, so use these results as a general reference only.
- Is my data stored anywhere?
- No. All calculations happen locally in your browser, and no dates or personal data are sent to or stored on any server.