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Period Calculator

Predict periods, ovulation, and fertile windows from cycle history.

Next 3 cycles

Estimates only — cycles vary. This is not medical advice; confirm important dates with a professional.

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What Is Period Calculator?

The Period Calculator predicts the next period, ovulation day, and fertile window from the last period start plus cycle and period lengths - then projects three full cycles ahead. Dates render as friendly weekday labels with an honest note that cycles vary.

Who Uses the Period Calculator?

Anyone tracking cycles for planning or peace of mind uses it for a quick forecast between app check-ins.

How to Use the Period Calculator

  1. Pick the first day of the last period.
  2. Set cycle length and period length.
  3. Read the forecast cards and three-cycle outlook.

Why Choose Our Period Calculator?

  • Period, ovulation, and fertile window together
  • Three-cycle projection, not just one date
  • Clear estimates-only guidance included

Try the Period Calculator above — it is free, fast, and works on any device. Bookmark this page to return whenever you need it.