Last updated: March 2026
What Is a Period Tracker?
A period tracker is a tool that helps you record and monitor your menstrual cycle. By logging the dates of your period each month, you build a personal history that reveals your cycle patterns — including average cycle length, period duration, and regularity.
This tracker goes beyond simple date logging. It uses your cycle history to predict future periods, estimate your fertile window, and approximate ovulation dates. The more cycles you log, the more accurate these predictions become.
Unlike most period tracking apps, this tool stores all data exclusively in your browser's localStorage. No data ever leaves your device — there are no accounts, no servers, and no third parties involved. Your health data belongs to you alone.
How It Works
Step 1: Log your period days. Tap dates on the calendar to mark each day of your period. Mark the first day of full bleeding as day 1 (skip any pre-period spotting). Continue marking each day until your period ends.
Step 2: Add optional details. For each period day, you can log flow intensity (spotting, light, medium, heavy), mood, symptoms like cramps or headaches, and personal notes.
Step 3: Watch predictions appear. After logging your first complete period, the tracker begins predicting your next period. After 2-3 cycles, predictions become significantly more accurate as the algorithm uses your personal average cycle length rather than generic estimates.
The color-coded calendar shows your logged period days in pink/red, predicted period days in gray, estimated fertile window in light blue, and estimated ovulation in green. The Stats tab provides detailed analytics including average cycle length, regularity score, and a visual cycle length history chart.
Remember to export your data periodically using the Settings tab, since browser data can be cleared. The export creates a JSON file you can import on any device to restore your tracking history.
Frequently Asked Questions
Is my data private?
Yes, all data is stored exclusively on your device using your browser's localStorage. Nothing is ever sent to any server. We have zero access to your health information.
How accurate are the predictions?
Prediction accuracy improves with more cycles logged. After tracking 3 or more cycles, predictions are typically within 1-3 days for people with regular cycles. The tool uses your personal cycle history, not generic averages.
Can I export my data?
Yes, you can export all your tracking data as a JSON file from the Settings tab. Use this for backup or to transfer your data to another device by importing the file.
What counts as day 1 of my cycle?
Day 1 is the first day of full menstrual bleeding — not spotting. Counting from the correct start date is important for accurate cycle length calculations and predictions.
What is a normal cycle length?
Most cycles range from 21 to 35 days, with 28 days being the average. Some variation between cycles (1-5 days) is perfectly normal. Consistently shorter or longer cycles may be worth discussing with your healthcare provider.
Can I use this as birth control?
No. This tool is for tracking and informational purposes only. The fertile window and ovulation estimates are approximations and should never be relied upon for birth control. Consult your healthcare provider for contraception advice.