Period Calculator

Period Calculator: Predict Your Next Period, Ovulation & Fertile Window

A period calculator is a helpful women’s health tool designed to estimate your next menstrual period, ovulation date, fertile window and overall menstrual cycle timeline. It helps you better understand your reproductive health using the first day of your last period, your average cycle length, your period duration and your cycle variation.

Whether you are tracking your menstrual cycle for personal health awareness, fertility planning, pregnancy preparation or simply managing monthly schedules, this free online period cycle calculator gives quick and easy predictions. It works for people with regular and slightly irregular cycles, and it is mobile-friendly and simple to use every day.

The calculator estimates your next expected period date, the earliest and latest expected dates, your ovulation day, your fertile window, your current menstrual cycle phase, the days remaining until your next period and your next three cycles.

Quick answer: if your last period started on June 1 and your cycle is 28 days long, your next period is expected on June 29. Ovulation is estimated for June 15, and your fertile window runs from June 10 to June 15. Enter your own dates above for your personal prediction.

What Is the Menstrual Cycle?

The menstrual cycle, also called the period cycle, is the monthly hormonal process that prepares the body for pregnancy. The cycle begins on the first day of menstruation and continues until the day before the next period starts. A typical cycle lasts between 21 and 45 days, although the average cycle length for many women is around 28 days. Hormones regulate ovulation, changes in the uterine lining and menstruation. The cycle has four main phases:

Tracking your cycle helps identify ovulation timing, fertile windows, hormonal patterns and possible irregularities.

How the Calculator Works

The calculator uses the standard calendar method. Your next period is your last period start date plus your cycle length. Ovulation is estimated at 14 days before the next period, because the luteal phase is fairly constant for most people. The fertile window is the 5 days before ovulation plus the ovulation day itself, which is 6 days in total.

Cycle variation adds a prediction range. If your cycle varies by 2 days, the earliest date is 2 days before the estimate and the latest date is 2 days after. If you enter a start date from several cycles ago, the calculator projects your cycle forward so the dates are always upcoming.

Who Can Use This Period Calculator?

Women tracking menstrual health, people trying to conceive, users monitoring irregular cycles, teenagers learning about menstrual cycles, fitness and wellness users who plan workouts and nutrition around their cycle, and women managing PMS symptoms. Knowing your cycle phase helps you prepare for mood changes, bloating, cramps and hormonal changes. If you are planning a pregnancy, the pregnancy calculator and the due date calculator can help with the next steps.

Tracking Your Cycle and Irregular Periods

To track effectively, record the first day of each period, the cycle length, your symptoms, any ovulation signs and how long your period lasts, every month. Stress, hormonal imbalance, weight changes, illness, exercise, medications, travel and poor sleep can all change the length of a cycle. The more months of data you have, the better your average becomes. Talk to a healthcare provider if your cycles are regularly shorter than 21 days or longer than 35 days, if you miss periods, or if your bleeding is very heavy or painful.

For Information Only

This calculator gives estimates for education and tracking. Ovulation timing varies between people and between cycles, so it should not be relied on as the only method of birth control, and it does not replace medical advice. Your dates are calculated in your browser, and nothing is saved or sent anywhere.

How to Use This Period Calculator

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