Cycle Tracker
Track your cycle and predict future periods — private and offline.
Stays on this device. Nothing you log is sent anywhere — no account, no server, no analytics.
period spotting predicted period estimated fertile window
Click a day to log your flow, any symptoms and a note. A run of days with light flow or more is a period; spotting is recorded but does not start one. Two or more days without bleeding end a period, so the next bleeding day begins the next cycle.
How predictions work. Your cycle length is the average of your last six cycles, measured from the first day of one period to the first day of the next — or the length you set. Ovulation is estimated as 14 days before the next period, because the second half of a cycle varies much less than the first, and the fertile window shown is five days either side of it. All of this is an estimate from averages: cycles vary, and this tool is not a form of contraception or a medical device. Talk to a clinician about irregular cycles.
Privacy. Everything is stored in this browser's own storage and never leaves the device — there is no account, no sync and no analytics on this site. Clearing site data, or Clear all data above, deletes it; Export JSON keeps a copy you control.
Is my data private?
Yes. It is stored only in this browser on this device and is never sent to any server. There is no account and the site runs no analytics.
Can I use the fertile window for contraception?
No. The window is an estimate from average cycle lengths, not a measurement of ovulation. It is not reliable enough to prevent pregnancy.
Why is my first prediction 28 days?
With only one period logged there is no cycle to average yet, so a typical 28 days is used until you log a second period — or set your own length in Settings.