MCPCalc

Menstrual Cycle Tracker

Estimate next period and fertile windows using min/max cycle lengths for irregular cycles.

Scratchpad (not saved)

days
days

What This Calculator Does

Estimate next period and fertile windows using min/max cycle lengths for irregular cycles.

It combines Last Period Year, Last Period Month, Last Period Day, Shortest Cycle to estimate Next Period Window, Estimated Fertile Window.

Formula & Method

Core equations: Next period window is estimated from the first day of the last period D_0 and cycle-length range [L_{min}, L_{max}]: D_{next,earliest} = D_0 + L_{min} D_{next,latest} = D_0 + L_{max} Fertile window is approximated from ovulation timing (about 10 to 19 days before the next period): D_{fertile,start} = D_{next,earliest} - 19 D_{fertile,end} = D_{next,latest} - 10 Inputs are applied in base units, then derived metrics are computed from the same equations and rounded for display.

Notation used in the formulas: R = Next Period Window; x_{1} = Last Period Year; x_{2} = Last Period Month; x_{3} = Last Period Day; x_{4} = Shortest Cycle; x_{5} = Longest Cycle.

Method summary: inputs are normalized to consistent units, core equations are evaluated, then secondary values are derived and rounded for display.

Use this estimator to plan around likely cycle windows, especially when cycle length varies month to month. It provides a range, not a diagnosis.

Inputs Used

  • Last Period Year: Used directly in the calculation.
  • Last Period Month: Used directly in the calculation.
  • Last Period Day: Used directly in the calculation.
  • Shortest Cycle: Used directly in the calculation.
  • Longest Cycle: Used directly in the calculation.

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