Track menstrual cycles, predict next periods and fertile windows with strong color-coded visualization. All data stays on your device.
The Period Tracker helps you understand your menstrual cycle by logging period dates and generating predictions. Enter your start and end dates for each cycle, and the tool calculates your average cycle length, average period duration, predicted next period, and estimated fertile window. Everything is displayed on a color-coded month calendar — red for logged period days, pink for predicted days, and green for fertile windows. Your data is stored entirely in your browser's localStorage, meaning no company, server, or third party ever sees your health information.
Cycle prediction based on your data
After logging two or more cycles, the tracker calculates your personal average cycle length and uses it to predict when your next period will start and how long it will last.
Fertile window estimation
The tool estimates your fertile window based on predicted ovulation timing, calculated from your average cycle length. The window is highlighted in green on the calendar.
Color-coded month calendar
Logged period days show in red, predicted period days in pink, and the estimated fertile window in green. See your cycle patterns visually across the entire month.
Cycle history with duration
Every logged cycle is listed with its start date, end date, and duration in days. Review your history or delete entries you no longer need.
Stats dashboard
Four stat cards show your average cycle length, average period length, next predicted period start date, and fertile window start date — updated automatically as you log more data.
Complete data privacy
All data lives in your browser's localStorage. No server, no account, no cloud sync. Your menstrual health information never leaves your device under any circumstances.
All tools share data — your calendar shows habits, periods, and countdowns automatically.