Cycle & Fertility Women’s Health

Period Calculator

Estimate your next period, ovulation day, fertile window, PMS days, and a simple cycle calendar. Works with regular and slightly irregular cycles.

Next Period Ovulation Fertile Window PMS & Calendar

All-in-One Period & Cycle Calculator

Enter your last period date and typical cycle details to see predicted dates. This tool is informational only and not medical advice.

This calculator uses average cycle assumptions and is not a substitute for professional medical advice, diagnosis, or treatment.

Period Calculator – Next Period, Ovulation, Fertile Days & PMS

This Period Calculator helps you estimate your next period, fertile window, ovulation day, PMS window, and a simple cycle calendar. It is built for informational and planning purposes only and does not replace advice from a doctor or healthcare professional.

What This Period Calculator Can Estimate

  • Next period start and end: Based on your last period date, typical cycle length, and period length.
  • Fertile window and ovulation: Uses an estimated luteal phase (commonly around 14 days) to approximate ovulation and the high-fertility window around it.
  • PMS window: Shows an approximate range of days before your next period when you may experience premenstrual symptoms.
  • Cycle calendar: Provides a preview of the next few predicted cycles including period and ovulation timing.

Inputs Used in the Calculator

  • First day of last period: The first day your most recent period started.
  • Average cycle length: Days from the first day of one period to the first day of the next (for many people this is around 28 days, but it can be shorter or longer).
  • Period length: How many days bleeding usually lasts.
  • Cycle variability (± days): Helps create an estimated range if your cycle is not exactly the same length every month.
  • PMS days: How many days before your period you typically notice premenstrual symptoms.
  • Luteal phase: The time between ovulation and the start of the next period, often estimated at around 14 days.

How the Estimates Work

The calculator projects your next period by adding your average cycle length to the date of your last period. Ovulation is estimated by subtracting the luteal phase length from the projected next period date. The fertile window is then built around the ovulation day, while PMS days are counted backward from the next expected period.

Important Limitations

  • The tool uses averages and simple mathematical models, so it cannot perfectly predict your cycle.
  • Illness, stress, travel, medications, and many health conditions can affect cycle timing.
  • Irregular cycles may be harder to estimate, even when you provide a variability range.

If your periods are frequently very irregular, very heavy, very painful, or you have concerns about fertility or missed periods, it is a good idea to speak with a qualified healthcare professional.

This calculator is meant to support planning and awareness, not diagnosis, contraception, or any form of medical decision-making.