Predict your next period, ovulation date, and fertile window based on your cycle. All calculations happen in your browser — your data is never shared.
🔒 Your health data stays on your device. Nothing is uploaded or tracked.
The first day of your most recent period
Typically 21–35 days; average is 28
How many days your period usually lasts
Number of future periods to show (1–12)
Next Cycle Predictions
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Next Period
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Ovulation
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Fertile Window
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Future Periods
How to Use
- Enter the first day of your most recent period.
- Set your average cycle length (days from the first day of one period to the first day of the next).
- Enter how many days your period usually lasts.
- Set how many future cycles to predict, then click "Calculate".
- View your next period, ovulation date, fertile window, and a multi-cycle calendar.
Features
- Predicts next period, ovulation date, and 6-day fertile window.
- Multi-cycle forecast — see up to 12 future periods at once.
- Days-until countdown for next period and ovulation.
- 100% private — all calculations in your browser, nothing sent to servers.
- Supports cycles from 21 to 45 days for regular and irregular cycles.
- No account, no app install, no subscription needed.
Use Cases
- Planning around your menstrual cycle for work, travel, or events.
- Identifying your fertile window when trying to conceive.
- Tracking cycle regularity and noticing changes over time.
- Preparing for upcoming periods by stocking supplies in advance.
- Monitoring cycle patterns to discuss with a healthcare provider.
FAQ
- How does the period calculator work?
- It uses your last period start date and average cycle length to predict future periods. Ovulation is estimated 14 days before the next period, and the fertile window is the 5 days before ovulation plus ovulation day.
- What is a normal cycle length?
- A normal menstrual cycle is 21 to 35 days, with 28 days being the average. Cycles may vary month to month due to stress, illness, weight changes, or hormonal factors.
- When is the fertile window?
- The fertile window is the 5 days before ovulation plus ovulation day (6 days total). Ovulation is usually 14 days before the next period. For a 28-day cycle, this is around day 14; for a 30-day cycle, around day 16.
- Is my data private?
- Yes. All calculations happen in your browser. Your health information is never sent to any server. Nothing is stored online — only optionally in your browser's local storage on your own device.
- How accurate is this calculator?
- The calculator provides estimates based on your entered cycle length and is most accurate for regular cycles. Cycles can vary due to stress, illness, or hormonal changes. Consult a healthcare professional for medical advice.