I Know My Body (IKnowMyBody) is a private period and perimenopause tracker app for iPhone and Android, made by 18v20. It helps you log your cycle and symptoms, predict your next period and spot patterns, while keeping every record on your own phone.

Yes. It's a free period tracker: logging, the calendar, period estimates and the perimenopause mode are all free. Premium is an optional one-time purchase that adds reminders, the 7-day planner, full insights and reports. There is no subscription.

No. There is no sign-up, email or password. You open the app and start logging.

On your phone only. This private period tracker has no servers and no cloud sync, and it contains no advertising or analytics tools. If you want a copy, you can save an encrypted backup file protected by a passphrase you choose.

Yes. Everything works without an internet connection, including logging, period estimates and insights.

The period tracker learns your own cycle length from what you log. Estimates show a likely date range that narrows as you log more cycles, with a plain note on how sure each estimate is.

Fertile days and an ovulation estimate are shown by default. You can turn them off in Settings if you'd rather not see them.

Yes. I Know My Body is also a perimenopause tracker. Switch to Perimenopause & menopause mode in Settings to track symptoms, hot flushes and night sweats, treatment changes and bleeding, and to prepare a summary for your appointment. Your period history comes with you.

Yes. Export an encrypted backup on your old phone and import it on the new one. Backups open on both iPhone and Android.

No. I Know My Body is a personal wellness tracker. Its estimates come from your own logs and are not medical advice, a diagnosis, a fertility test or a method of contraception. Talk to a doctor or nurse about anything that worries you.