A period cycle calculator is a free online tool that helps you predict your next period date, ovulation day, fertile window, and pregnancy chances based on your cycle data. You simply enter the first day of your last period, your average cycle length, and period duration to get a full cycle report instantly.

To calculate your next period date, enter the first day of your last period and your average cycle length. The calculator adds your cycle length to that start date and gives you the predicted date. For most women with a 28-day cycle, the next period arrives exactly 28 days after the first day of the previous one.

Ovulation typically happens 14 days before your next expected period. Our calculator uses your luteal phase length — which defaults to 14 days — and counts back from your predicted next period date. This gives you the most likely ovulation day based on your personal cycle pattern.

The fertile window is the 6-day period during which pregnancy is possible. It includes the 5 days leading up to ovulation and ovulation day itself. Sperm can survive inside the body for up to 5 days, so intercourse before ovulation can still result in conception when the egg is finally released.

A normal menstrual cycle ranges from 21 to 35 days, with 28 days being the most common average. Your cycle is counted from the first day of one period to the first day of the next. Cycles that fall outside the 21–35 day range regularly may be worth discussing with a healthcare provider.

This tool uses the standard fertility awareness formulas used by health professionals to estimate key cycle dates. However, real-world factors like stress, illness, travel, and hormonal fluctuations can shift your cycle. For medical decisions — especially around conception or contraception — always consult a qualified gynecologist.

No. All calculations happen entirely in your browser. We do not collect, store, or transmit any personal health data you enter into this tool. Your cycle information stays completely private on your own device.

Yes, completely free. No account, no subscription, and no hidden fees. Open the tool, enter your details, and get your full cycle report — including a downloadable PDF — at no cost.