Ebb

Ebb records your menstrual cycle, predicts when your next period is likely, and reminds you beforehand, all on your device.

Release builds ship without Android's INTERNET permission, so the app can't send your data anywhere: Android enforces it, and you can check the permission list yourself. There's no account, no sync, no analytics and no ads, and Ebb opts out of Android's cloud backup.

• Predictions as a date range with a stated confidence, not a false single date. The method is a plain, explainable median of your own recent cycles.
• A calendar for logging and correcting past periods, plus optional notes, a day rating and how you felt.
• Charts of what you logged, without drawing conclusions from it.
• Local reminders that work with no signal.
• Track someone else too (a child learning their cycle), with their own settings.
• Optional groups for circles who compare cycles together, and optional moon phases.
• Move to a new phone by scanning a few QR codes, with no network involved. Backups are plain, documented JSON.
• The fertile-window estimate is off by default and clearly labelled as not contraception.

Free and open source under the GNU GPL, with no premium tier.