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Fertility & Ovulation Calculator

Fertility & Ovulation Calculator
Predict your most fertile days based on your average cycle length.

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Understanding Your Fertile Window

An ovulation calculator estimates your most fertile days. Knowing this "fertile window" can help you time intercourse to increase your chances of conceiving.

How It Works

Ovulation typically occurs about 14 days before your next period begins. This calculator uses your average cycle length and the first day of your last menstrual period (LMP) to predict your next ovulation date and the six-day window when you are most fertile.

Fertile Window

Your fertile window includes the five days leading up to ovulation and the day of ovulation itself. Conception is most likely to occur in the two to three days before you ovulate.

Disclaimer

This is an estimation and should not be used for contraception. Cycle lengths can vary, and for the most accurate information, it's best to track your cycle over several months and consult with a healthcare provider.

Logic & Formulas

The calculation is based on the calendar method and the assumption that ovulation occurs 14 days before the start of the next menstrual cycle.

  1. Next Period Date: First, the estimated start date of your next period is calculated.

    Next Period = Last Period Date + Cycle Length (in days)

  2. Estimated Ovulation Date: Ovulation is then estimated by subtracting 14 days from the next period date.

    Ovulation Date = Next Period Date - 14 Days

  3. Fertile Window: The fertile window is the 6-day period ending on the day of ovulation.

    Window Start = Ovulation Date - 5 Days

All date calculations are performed using the `date-fns` library for accuracy.