Period & Cycle Calculator

Estimate your next period, fertile window and ovulation day from your cycle length.

Next period (estimated)

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Next period (estimated)Check inputs

Educational estimate only — not medical advice. Talk to a healthcare professional about your health.

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Quick answer

With a 28-day cycle starting March 1, the next period is expected around March 29, with ovulation around March 15.

How it works

Cycles are counted from the first day of one period to the first day of the next. Ovulation is estimated at 14 days before the next period, and the fertile window covers the five days before it plus the day after.

Formula

Next period = last period + cycle length · Ovulation ≈ next period − 14 days

Assumptions & limitations

Results are rounded for display.

Frequently asked questions

How accurate is this?

Cycles vary, so treat dates as estimates. Tracking several cycles improves accuracy.