Flo vs Euki: Mass Market Data Broker vs Privacy-First Free App

The download numbers tell one story; the FTC enforcement action tells another

Flo is the most-downloaded period tracker in the world. Its prediction algorithms benefit from the largest dataset in the category. Its feature set is genuinely comprehensive.

The FTC also took enforcement action against Flo in 2021 for sharing users’ reproductive health data with Facebook, Google, and Flurry without consent. A class action over the same conduct settled for $59.5M in September 2025 (Reuters 2025-09-25). These are public facts from federal records.

Euki is a nonprofit-backed app with a fraction of Flo’s downloads. Its UI is functional rather than polished. Its prediction accuracy is lower because it doesn’t have Flo’s dataset. It is also free, on-device, account-free, and has no documented history of selling user health data.

The feature gap is smaller than it appears

The common assumption is that private apps sacrifice features. Euki covers period tracking, fertile window prediction, sexual health education, contraception logging, STI information, and pregnancy tracking. It runs on both iOS and Android.

The gaps compared to Flo are real but narrower than expected: Flo’s predictions are more accurate (more training data), Flo has cross-device sync (Euki doesn’t), and Flo has a more polished interface. If those things matter more than the documented data violations, Flo is a functional choice. If they don’t, Euki covers the essential use case at no cost.

The cross-device problem

Euki’s main practical limitation is the lack of sync. Your data lives on your phone. If you get a new phone or use a tablet, starting over is the only option (manual CSV export aside). Flo handles this through cloud sync — which requires the server-side architecture that creates the subpoena risk.

Floriva’s opt-in encrypted sync addresses this: data is encrypted on your device before transmission, so the sync infrastructure cannot access plaintext health data. The encryption key stays with you.

Cost and the nonprofit model

Euki is free because the National Institute for Reproductive Health funds it through grants and donations. There is no subscription, no ads, no freemium upsell. Flo’s free tier is ad-supported and limited; full privacy requires paying for Anonymous Mode. Floriva is $2.99/mo — less than either Flo Premium or Stardust Premium.

Verdict

Euki is the better choice if privacy is a priority and you don't need cross-device sync. It's free, on-device, and has no data-selling history. Flo has the larger feature set and better prediction accuracy from its dataset, but a documented history of sharing your most sensitive health data without consent. The FTC enforcement action and class action are public record.