Period Calculator
Predicted Period Dates
Enter the first day of your last period, your average cycle length, and typical period duration to predict your next several cycles.
Parameters
Next Period
| Cycle | Period Dates |
|---|
Understanding Menstrual Cycle Prediction
This calculator projects your next several period start and end dates forward from your last period, using simple cycle-length arithmetic — useful for general planning, regardless of whether you're trying to conceive.
Cycle Length Varies by Person
The average cycle is 28 days, but a normal range spans roughly 21-35 days — use your own tracked average for the best prediction.
Period Duration
A typical period lasts 3-7 days. This calculator uses your entered duration to project both start and end dates for each cycle.
Tracking Improves Accuracy
The more consistently you track your cycles, the more reliable your personal average cycle length becomes for future predictions.
Not Pregnancy-Specific
This tool is for general cycle tracking — see our Ovulation Calculator if you're specifically trying to time conception.
Important Limitations
- Assumes cycle regularity: Predictions become less reliable the more irregular your actual cycles are.
- Doesn't account for external factors: Stress, illness, travel, and hormonal changes can all shift your actual cycle timing.
- Further-out predictions are less certain: The 4th, 5th, and 6th projected cycles compound any drift in your actual average cycle length.
Key Takeaways
- Simple forward projection. Each predicted period is your last period plus a multiple of your average cycle length.
- Use your own tracked average. A cycle-tracking app or journal over a few months gives a more accurate input than guessing.
- Near-term predictions are more reliable. Confidence decreases for cycles further in the future.
- Consult a professional. Significant cycle irregularity, missed periods, or severe symptoms should be evaluated by a gynecologist rather than tracked by prediction alone.