What is the difference between Stardust and Clue?

Stardust is a US-based period tracker marketed as privacy-first with an astrology-tied angle and $29.99/year pricing. Clue is a Berlin-based tracker (Biowink GmbH) that has been around longer, operates under GDPR, has academic research partnerships with Oxford and Stanford, and costs $39.99/year for Clue Plus. Stardust's privacy claims have been contested. Clue has no comparable enforcement history.

Are Stardust's privacy claims accurate?

Stardust's marketing uses zero-knowledge language, but researchers who examined the architecture found that data is stored in a form Stardust can decrypt on their servers. That does not match a strict zero-knowledge definition. The privacy framing is stronger in marketing than in the underlying technical architecture. See our guide on Stardust privacy claims for a full breakdown.

Does Clue sell user data?

Clue does not have a documented record of selling user health data. Biowink GmbH operates under GDPR out of Berlin, its business model is subscription-based rather than ad-supported, and it has no FTC enforcement history. GDPR still allows compelled disclosure under valid legal process, so the commercial picture is cleaner than the legal-process picture.

Which is cheaper, Stardust or Clue?

Stardust costs about $29.99/year. Clue Plus costs about $39.99/year. Stardust is cheaper on annual price. Price is not the same as privacy value: the architecture difference between them is small because both use server-side storage. Pay for whichever feature set you actually use.

Is there a period tracker with no cloud storage?

Yes. Floriva stores cycle data only on your device using encrypted local storage, with no account and no server copy. Drip (Android) and Euki also use on-device storage by default. If you want no server-side copy of your cycle data at all, on-device-only trackers are the only architecture that delivers that.

comparisons

Stardust vs Clue: Privacy, Features, Architecture (2026)

Stardust markets zero-knowledge but stores data server-side. Clue is GDPR-compliant with no FTC actions. Neither uses on-device-only storage.

Two apps, different privacy claims Stardust and Clue both position themselves as safer choices for period tracking. Stardust uses zero knowledge marketing language and an astrology tied differentiator. Clue uses GDPR jurisdiction, a subscription business model, and academic research partnerships. We compared the two because users considering them are usually trying to move off Flo or another data selling app. They want a tracker with a credible privacy story. The question is whether either app delivers privacy at the architecture level, or only at the marketing level. How Stardust stores data Stardust is a US based app marketed as privacy first. Its public facing copy invokes zero knowledge encryption. When researchers examined the actual storage model, they found that user data sits on Stardust servers in a form the company can decrypt. That is not what zero knowledge means. True zero knowledge means the encryption keys never leave the user's device, so even the service provider cannot read the stored data. Stardust's architecture does not match that standard, based on the reviews referenced in our Stardust privacy claims guide. The marketing implies one thing. The architecture do