Period Calculator

This calculator estimates the timing of your next period, fertile window, and likely ovulation date using the cycle information you enter. It is meant to help you plan around a typical cycle pattern.

Because real cycles can vary from month to month, the results are best treated as a planning estimate rather than an exact prediction.

The average number of days in your cycle has a direct effect on the projected dates. Shorter cycles usually move the next period and ovulation earlier, while longer cycles push them later.

If your cycle is irregular, tracking several months can give you a more realistic average and make the forecast more useful.

Cycle estimates can be less predictable during adolescence, postpartum recovery, perimenopause, after stopping hormonal birth control, or when stress, illness, travel, or major training changes affect the body.

If you are trying to conceive, avoiding pregnancy, or concerned about unusual symptoms, this calculator should not replace professional medical guidance.

This page estimates future cycle dates from the cycle length and last period information you enter. Menstrual cycles can vary naturally, so the dates shown here are planning estimates rather than medical confirmation of ovulation or fertility.

• U.S. Office on Women's Health: Your menstrual cycle
• American College of Obstetricians and Gynecologists: Fertility awareness and the fertile window