Enter your last few period start dates. Instead of a fake-precise date, you'll get what's honestly knowable: a realistic range, with a confidence level.
Add the first day of each of your last 3–12 periods. The more you add, the tighter the window; 6 or more is ideal. Nothing you enter leaves this page: the math runs right here in your browser.
Ebb runs a full prediction engine on your phone: the range updates every time you log, tells you how confident it is, and never uploads your data anywhere. Free tier forever.
Download on the App StoreThis calculator is educational, not medical advice, and not a contraception method. It estimates a likely window from the dates you enter using the spread of your own cycles (the same idea behind Ebb's on-device engine, simplified). Cycles vary with stress, sleep, illness and more, and if yours worry you, that's a good reason to talk to a clinician. Your dates are processed only in your browser and never sent or stored.