Period Cycle Length Calculator
Calculate your average cycle length, variation, and regularity from multiple tracked periods.
Results
Visualization
How It Works
Tracking multiple cycles reveals your average cycle length and how regular you are. This information is valuable for predicting ovulation and identifying potential issues.
The Formula
Average = Sum of Cycle Lengths / Number of Cycles
Standard Deviation = sqrt(variance) — measures consistency
Variables
- Range — Difference between longest and shortest cycle
- SD — Standard deviation — lower means more regular
Worked Example
Cycles of 27, 28, 29, 28, 30 days: Average = 28.4, Range = 3, SD = 1.0 — Regular.
Practical Tips
- Track at least 3-6 cycles for a meaningful average.
- A cycle range of 7+ days may warrant discussion with your doctor.
- Normal cycle length ranges from 21 to 35 days.
- Cycle length often varies more during perimenopause and adolescence.
- Consistently short cycles (<21 days) or long cycles (>35 days) should be evaluated.