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Menstrual Cycle Calculator — Free Online Calculator

Predicts upcoming period dates from cycle length and last period.

What is it?

The menstrual cycle tracker logs the start date of recent periods, calculates cycle length statistics, and predicts the next period start date.

Formula

Cycle length = Days from start of one period to start of the next Average cycle = mean of recent cycle lengths Next period start ≈ Last period start + Average cycle length

Example

Last 3 period starts: 1 Jan, 30 Jan (29 days), 26 Feb (27 days). Average cycle = 28 days. Next period ≈ 26 Feb + 28 = 26 Mar.

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