How to Calculate Period
What is Period?
A period (menstrual cycle) calculator predicts future menstruation dates based on cycle length and period duration. The average cycle is 28 days, but cycles from 21 to 35 days are normal. Tracking helps identify irregularities and plan around key life events.
Step-by-Step Guide
- 1Record the first day of your last period (day 1)
- 2Add cycle length to find the next period start date
- 3Add period length to find the end date
- 4Repeat for subsequent cycles
Worked Examples
Input
Last period: 1 March · 28-day cycle
Result
Next period: 29 March · Fertile window: ~15–19 March
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