Period Calculator
Predict upcoming period dates, ovulation window and fertile days from your last period and cycle length.
Local processingPeriod Calculator
What is Period Calculator?
Period Calculator estimates the dates of upcoming periods based on the first day of the last period and the usual cycle length. It also shows an estimated ovulation day and fertile window.
How It Works
Cycle dates are projected by adding the cycle length repeatedly. Ovulation is estimated about 14 days before the next period, with a fertile window spanning the preceding five days plus ovulation day.
Common Use Cases
- Planning around upcoming periods
- Estimating fertile days for conception planning
- Preparing questions for a healthcare appointment
- Tracking cycle regularity
Technical Details
Uses calendar arithmetic in the browser. Predictions are estimates and may differ from actual cycles, especially when cycles are irregular.
How to Use
Enter your input above. The result updates automatically. Use the copy button to copy the result.
Privacy
All processing happens in your browser. Your data is never uploaded to any server.
FAQ
How accurate are the predictions?
Predictions assume a regular cycle length. They are estimates and should not be used as contraception or as a substitute for medical advice.
Is my data uploaded to a server?
No. Everything runs locally in your browser. Your input never leaves your device.
Does Period Calculator work on mobile?
Yes. The interface is responsive and works in modern mobile browsers without installing an app.