Mozilla's 2026 Period Tracker Privacy Report: Stardust Shared Health Data, Euki Was the Only Safe App

Period Calendar (score: 6/10) — Sends device ID numbers and other identifying information to Google and the advertising company InMobi. Mozilla reports there is no way for users to prevent this data transmission .

Planned Parenthood's Spot On (score: 5/10) — The app itself does not share health data, but when users access certain features — such as the AI chatbot "Roo" or a healthcare provider search tool — they are redirected to Planned Parenthood's website via an in-app browser. That website shares information about what kind of healthcare the user is seeking (including whether they are looking for HIV testing or gender-affirming care) with the analytics company AB Tasty, and also sends browsing data to Google, Microsoft, TikTok, and Pinterest .

Flo (score: 7/10) — Collects extensive health data (cycle details, moods, symptoms, fertility goals) on its own servers but does not share that health data with third parties. Optional ad tracking sends encrypted data to partners like AppsFlyer, Moloco, and Google Firebase, but the privacy toggle works as advertised .

Clue (score: 8/10) — Stores user health data on its own servers under German/EU privacy law and does not share sensitive health data with third parties during normal app use. However, it does transmit enough metadata (timestamps, in-app behavior) that outside services can tell when a device is using Clue .

Euki (score: 10/10) — "Squeaky clean" rating — The only app that stores all health data locally on the user's device. No account creation is required. Mozilla's testing found no health data leaves the device during core features like cycle and symptom tracking. The only minor caveat is that certain educational resources open in an in-app browser that loads web trackers, but those trackers are assigned fresh identifiers each time and cannot see the user's health data .