All calculatorsAbout UsContact UsPrivacy PolicyTerms & Conditions

Period Calculator

Enter your last period and cycle length to predict your next one.

Next period

—

Current cycle day

—

What this calculator does

This calculator estimates your next period date and shows which day of your current cycle you're on today, based on the first day of your last period and your average cycle length.

Worked example

With a last period starting August 6, 2026 and a 28-day cycle, the next period is estimated around September 3, 2026, and on September 2, 2026you'd be on cycle day 28.

Common mistakes

  • Using the wrong start date. Cycle day 1 is the first day of bleeding, not the last day of your period or the day you expect your next one.
  • Assuming every cycle is identical. Cycle length naturally varies month to month — treat the prediction as an estimate, not a guarantee.
  • Confusing this with ovulation timing. Ovulation typically occurs about two weeks before the next period, not right at the start of a new cycle.

Frequently asked questions

How is my next period date estimated?+

We add your average cycle length to the first day of your last period. For example, a 28-day cycle starting May 1 puts the next period around May 29.

What does 'cycle day' mean?+

Cycle day 1 is the first day of your period. The cycle day shown is how many days have passed since then, looping back to 1 once a new cycle begins.

How accurate is this?+

This is a calendar-based estimate assuming a consistent cycle length. Real cycles vary due to stress, illness, travel, and many other factors — tracking several cycles gives a more reliable personal average than a single one.

How is this different from the ovulation calculator?+

This tool focuses on predicting your next period and current cycle day. The ovulation calculator focuses specifically on your estimated fertile window and ovulation day, which falls roughly two weeks before your next period.

Related calculators

Age CalculatorCalculate exact age in years, months, and days.Anniversary CalculatorFind your next anniversary and years together. Next Birthday CalculatorFind how many days until your next birthday.Days Alive CalculatorFind out how many days you've been alive.