What's a normal cycle length?
21-35 days is normal range. Average is 28 days but individual variation is common.
Health Fitness
Menstrual Cycle Calculator
Estimate menstrual cycle with quick inputs.
Fast, practical estimates
Adjust inputs for the most useful result.
What this calculator does
A menstrual cycle calculator tracks cycle phases: menstruation, follicular, ovulation, and luteal. Average cycle length is 28 days but ranges from 21-35 days. Tracking helps predict periods, identify fertile days, and detect irregularities.
How it works
Enter first day of last period and average cycle length. The calculator predicts next period and identifies cycle phases.
Formula
Next Period = LMP + Cycle Length. Ovulation ≈ Cycle Length - 14 days. Luteal phase is typically 14 days.
Tips for using this calculator
- Track 3+ cycles for accurate predictions
- Cycle length can vary month to month
- Stress, travel, and illness affect cycle timing
- Apps make tracking easier
- Consult doctor for cycles <21 or >35 days
Frequently asked questions
Why is my cycle irregular?
Stress, weight changes, exercise, travel, and hormonal conditions can cause irregularity. Persistent irregularity warrants medical evaluation.
Can I get pregnant during my period?
Unlikely but possible, especially with shorter cycles where ovulation occurs earlier.