How to use this tracker
Log in, then enter the start date of your last period and tap Log period. Each time a new period starts, log its first day. After two or more logs, the tracker learns your average cycle length and predicts your next period, the fertile window and estimated ovulation day. You can also set your cycle and period length manually in Settings.
Understanding your cycle
A menstrual cycle is counted from the first day of one period to the first day of the next. A typical cycle is around 28 days but anything from 21 to 35 days is common and normal. Ovulation usually happens about 14 days before the next period, and the days leading up to it are the most fertile. Because cycles naturally vary month to month, these predictions are estimates that get more accurate the more you log — they are not a substitute for a doctor’s advice or a reliable contraceptive method.
Your privacy
Cycle data is sensitive, so it is treated as strictly private. Your logs are stored against your account and protected by row-level security, meaning only you can read your own records. Nothing is shared or shown publicly.
Frequently asked questions
Is my period data private?
Yes. Your logged dates are saved only to your own account and protected by row-level security in the database, so no other user can read them. Predictions are calculated from your data alone.
How does it predict my next period?
Your cycle length is averaged from the gaps between the period start dates you log (it uses 28 days until you have two or more logs, or whatever you set manually). Your next period is predicted by adding that cycle length to your most recent start date.
How are ovulation and the fertile window estimated?
Ovulation is estimated as 14 days before your next predicted period. The fertile window is the five days before ovulation plus ovulation day, since sperm can survive several days. These are estimates, not a precise test.
Do I need to log in?
Yes, because your cycle history is private and synced to your account so you can see it on any device. Create a free account with just an email and password.
Can I rely on this for contraception?
No. Cycle-based predictions are estimates and cycles vary. Do not use this tool as a contraceptive method or as medical advice — consult a doctor for health decisions.