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Menstrual Cycle Calculator

Predicted next period and fertile window.

Predict the next several menstrual periods, ovulation dates, and fertile windows from the first day of your last period and an average cycle length.

Priya Venkatesan By Priya Venkatesan
Reviewed by Dr. Helena Ortiz
Published Last reviewed 1 min read

Inputs

days

Results

Enter values and click Calculate to see results.
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How to use this calculator

  1. Fill in the inputs above using the units you already have.
  2. Values update automatically as you type — no submit button needed.
  3. Hover any result row for the underlying formula and intermediate values.

Formula

Next period = LMP + cycle. Ovulation ≈ next period − 14 days. Fertile window = ovulation − 5 days through ovulation.

In depth

Predict the next several menstrual periods, ovulation dates, and fertile windows from the first day of your last period and an average cycle length.