Period Tracker — Predict Next Period and Cycle Length Free
Predict your next period, see a colour-coded 3-month calendar and a forecast of your next 6 periods. Tracks PMS, fertile window and ovulation. Private — all data stays in your browser.
Last updated: June 2026
Predictions
- Next period starts
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- Next period ends
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- Days until next period
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- Ovulation (estimate)
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- Fertile window
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- PMS window
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3-month forecast
Your next 6 periods
| Cycle | Start date | End date | Days until |
|---|
Cycle history (saved on this device only)
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Medical Disclaimer: This tool provides estimates based on average cycle patterns. Individual cycles vary significantly. It is not a substitute for medical advice or a method of contraception. Consult a doctor for medical concerns or irregular cycles.
About this tool
Know when your period is coming
A period tracker helps you see the month ahead instead of being caught off guard. Enter the first day of your last period and your usual cycle length, and the tool predicts when your next period will start and end, how many days away it is, and projects your next six cycles so you can plan around them.
The colour-coded calendar puts everything in context: red for your predicted period, green for your fertile window, orange for the PMS days just before your period, and purple for your estimated ovulation day. Seeing all of these together makes it easier to understand your cycle as a whole rather than just one date. If your cycle is irregular, log your actual period start dates over a few months and the tracker will work out your real average cycle length for more personal predictions.
Privacy is the whole point of doing this in a simple tool rather than an app that asks you to sign up. Everything is calculated in your browser, and your logged dates are stored only on your own device, never uploaded. You can clear your history at any time. Keep in mind these are estimates based on averages, not medical predictions, so for irregular cycles or health concerns, please speak to a doctor.
How it works
Three quick steps — no account, nothing uploaded to a server.
Enter your last period
Pick the first day of your most recent period.
Set your cycle length
Adjust cycle length and period duration with the sliders.
See your forecast
Next period, calendar and 6-cycle forecast appear instantly.
General health information related to this tool is available from the HHS Office on Women's Health (womenshealth.gov). Last checked July 2026.
FAQ
Frequently asked questions
How does a period tracker predict my next period?
It takes the first day of your last period and adds your average cycle length to estimate the start of your next one. From there it projects several cycles ahead. So if your last period started on the 1st and your cycle is 28 days, your next period is predicted around the 29th. The more regular your cycle, the more accurate the prediction.
What is the difference between a period tracker and an ovulation calculator?
An ovulation calculator focuses on your fertile window, the days you are most likely to conceive. A period tracker focuses on when your period will arrive and gives you a multi-month calendar and a forecast of your next several periods, along with PMS and ovulation estimates. Use the ovulation tool for conception planning and this one for knowing when to expect your period.
How accurate is the prediction?
Predictions are based on average cycle patterns, so they work best for regular cycles. Real cycles vary from month to month due to stress, illness, travel, diet and many other factors, so treat the dates as estimates. Logging your actual period start dates over a few months lets the tool calculate your real average cycle and improve its guidance.
Is my cycle data private?
Completely. All cycle data stays in your browser only. Nothing is ever sent to a server, and there is no account. Your logged dates are stored locally on your device, and you can clear them at any time with the Clear history button or by clearing your browser data.
What do the calendar colours mean?
Red marks your predicted period days, green marks your estimated fertile window, orange marks the PMS window in the few days before your period, and purple marks your estimated ovulation day. The colours give you an at-a-glance view of the month ahead.
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