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Menstrual Cycle Calculator

Estimate your next period, ovulation date and fertile window.

Formula v1.0.0GlobalMethodologymenstrual-cycle-v1
How this is calculated
Ovulation ≈ next period date − 14 days (luteal phase)

Assumptions used in this calculation

  • Regular cycles: Assumes a consistent cycle length, actual ovulation timing varies and this isn't a substitute for medical tracking methods.

About this calculator

Estimate your next period date, ovulation date and fertile window from the first day of your last period and your average cycle length, based on the standard 14-day luteal phase.

Worked example

Last period started 1 Jan, 28-day average cycle

Result: Next period ≈ 29 Jan, ovulation ≈ 15 Jan

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