CalculatorsCycle estimates

Menstrual Cycle Calculator

Map an estimated cycle timeline, including the next period and likely ovulation window.

Your details

Enter only the information needed for this estimate.

Start with the first day of full bleeding.

Use an average from recent cycles if you have it. (days)

More precise estimate

Count the days you usually have menstrual bleeding. (days)

Calculator entries stay in this browser session to produce this result. This tool does not save them in browser storage.

Complete the fields and select “Map my cycle” to see your estimate.

What the timeline shows

Cycle day 1 is the first day of menstrual bleeding. The next cycle begins when the next period starts. The calculator projects that date from the average cycle length you enter.

It also offers a calendar-based fertile window. That window is an estimate because ovulation does not always happen on the same cycle day.

Build a more useful average

Record the first day of each period for several cycles. If your cycle lengths vary, the range can be more informative than a single average.

  • A cycle is counted from one period start date to the next.
  • Spotting before full flow is usually not counted as cycle day 1.
  • Recalculate when your recent cycles differ from your older pattern.

Limits of this estimate

  • A calendar cannot confirm hormone levels, ovulation, fertility, or the reason for a cycle change.
  • Hormonal contraception, postpartum changes, breastfeeding, perimenopause, illness, and stress can make projections less useful.
  • The date range is not a contraceptive method.

Common questions

How should I use this estimate?

Use it as a planning starting point, then compare it with your own experience and any guidance from a qualified health professional.

Is this medical advice?

This calculator provides educational calendar estimates, not medical advice or diagnosis. Contact a qualified health professional about persistent cycle changes or symptoms that concern you.

What happens to what I enter?

The calculator uses the values in your current browser session to produce the result. It does not save them in browser storage.