Period Calculator

Estimate your next period date, current cycle day, fertile window, ovulation day, and upcoming period dates using your menstrual cycle details.

Please enter your last period date, cycle length, and period duration correctly.
This calculator gives an estimate based on average cycle patterns. Menstrual cycles can vary due to stress, illness, travel, hormonal changes, breastfeeding, medication, or contraception. It should not be used as a medical diagnosis or as the only method of contraception.
Expected Next Period

Your Current Cycle

Expected Period End

Fertile Window

Estimated Ovulation

Upcoming Period Predictions

Calendar Preview

Period Days
Fertile Window
Ovulation Day
Today

How This Period Calculator Works

Your menstrual cycle is counted from the first day of your period to the day before your next period starts. For many people, a cycle is around 28 days, but cycles can be shorter or longer and still be normal.

This calculator estimates your next period by adding your average cycle length to the first day of your last period. It also estimates ovulation by counting back around 14 days before your next expected period.

  • Period days are based on the duration you enter.
  • Fertile window is estimated around the days before and after ovulation.
  • Ovulation day is an estimate and may vary from cycle to cycle.
  • Upcoming periods are predictions and may change if your cycle is irregular.

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