Which is more private: Flo, Clue, Stardust, or Dew?

By architecture, Dew is the most private of the four — it stores data on your device with no account and no server copy. Clue is a careful, GDPR-based operator but stores data on its servers. Flo settled a 2021 FTC matter over data-sharing allegations and is server-based. Stardust drew criticism in 2022 reporting (TechCrunch) over phone-number sharing and law-enforcement language it later revised. Roughly: Dew is the most private; Clue the most private of the server-based mainstream apps; Flo and Stardust depend on the specific concern. Verify each app's current policy yourself.

What happens to my cycle data if I uninstall each app?

With Dew (on-device), uninstalling removes your data from the device — there's no server copy left behind. With server-based apps like Flo, Clue, and Stardust, uninstalling the app leaves your account and data on their servers until you separately delete the account. See our guide on deleting period tracker data.

Is my cycle data encrypted in these apps?

Most encrypt data in transit and at rest on their servers, but server-side encryption still lets the company read your data. The stronger form is end-to-end encryption, where only your devices hold the keys — that's how Dew's optional iCloud sync and Apple Health work, meaning even the provider can't read the contents.

Which of these trackers works without an account?

Dew works with no account at all. Flo, Clue, and Stardust require an account (Flo offers an Anonymous Mode that de-links identity but still stores data on its servers). No account means there's no identity tied to your cycle to share or surrender.

Flo, Clue, Stardust, Dew: a privacy comparison

Four trackers, six privacy questions, side by side. Where your data lives, what's encrypted, who can read it, and what survives an uninstall.

"Privacy" in period app marketing has become a word that means everything and therefore nothing. Every app claims it. We wanted to know what it actually meant for the four most-installed cycle trackers in 2026.

Below: the same six questions asked of each app, answered from public privacy policies, the FTC's public case record, and the apps' own technical documentation. Plain facts, no FUD.

A note on sourcing: this reflects public records and each company's published privacy policy as of June 2026. Companies change their practices and may dispute these characterizations — verify current policies yourself. Where we mention regulatory action (Flo) or reporting (Stardust), those matters were settled or revised without any finding of wrongdoing here, and nothing on this page is intended as a statement that any company broke the law.

The six questions

Where does your data physically live?
Is the data encrypted at rest? With what key?
Does the app share data with third parties, and if so, who?
Is there a way to use it without an account?
How long does account deletion take, and what survives?
What happens to your data if the company is acquired or goes bankrupt?

1. Where does the data live?

Flo: AWS servers, primarily US East.
Clue: AWS servers in Germany (EU jurisdiction).
Stardust: AWS servers, US.
Dew: Your iPhone, locally. Optional sync to your own iCloud Private Database. Dew has no servers of its own.

2. Encryption at rest?

Flo: At rest on Flo's servers, encrypted with Flo's keys. They can decrypt it; you can't.
Clue: Same — encrypted at rest on Clue's servers with Clue's keys.
Stardust: Same.
Dew: Local SQLite database, OS-level encryption when the phone is locked. iCloud sync uses Apple's CloudKit Private Database, which is end-to-end encrypted with your iCloud keys — Apple cannot read it, Dew cannot read it.

What this means: Server-side encryption protects against a stolen hard drive at AWS. It does NOT protect against a subpoena to the company — they have the keys to decrypt, so they can be compelled to. End-to-end encryption with your own keys does protect against subpoena because nobody else can decrypt.

3. Third-party sharing?

Flo: The FTC's 2021 complaint alleged that earlier Flo had shared data with third parties including Facebook, Google, and AppsFlyer; Flo settled (no fine, no admission of wrongdoing). Its current policy lists "service providers" without naming ad partners, and Anonymous Mode lets you skip the account tie. Check the live policy for what analytics it uses today.
Clue: Shares aggregated, anonymized data with research partners (Stanford, Oxford, named in their transparency report). Does not share with ad networks.
Stardust: TechCrunch reported in 2022 that it shared users' phone numbers with a third-party analytics provider; Stardust revised its practices afterward and disputed parts of the coverage. Check its current policy for what it shares today.
Dew: No third-party SDKs at all. Anonymous, opt-out usage analytics through TelemetryDeck — only feature taps, never cycle data. Crash reports through Apple's own MetricKit. Privacy policy.

4. Usable without an account?

Flo: No. Account creation is required at install.
Clue: No. Account required.
Stardust: No. Account required.
Dew: Yes. There is no account system. Install, open, log.

5. Account deletion time / what survives

Flo: Within 30 days per its policy. Anonymized aggregate already shared with third parties isn't pulled back, and per the FTC's 2021 case any data shared earlier with third parties is outside Flo's control.
Clue: Within 30 days. Aggregated anonymized data used in published research isn't pulled back (research-ethics norm).
Stardust: Within 30 days per policy. Anything previously shared with third parties not under their control.
Dew: Immediate. "Delete All" in Settings wipes the local database and force-pushes the truncate through your iCloud sync so other devices converge before sign-out. Nothing on Dew's servers because Dew has no servers.

6. What happens if the company is acquired or goes bankrupt?

Flo: Data is an asset on Flo's balance sheet. In an acquisition, it transfers. In a bankruptcy, it could be sold (this is what happened to Vine, MoviePass, and several health apps).
Clue: Same risk in principle, mitigated by GDPR (the data can't be transferred to a buyer who can't honor GDPR commitments).
Stardust: Same risk as Flo.
Dew: Even if Dew shuts down tomorrow, your data is in your own iCloud Private Database — Dew cannot transfer it, sell it, or look at it. Your data outlives the company.

The summary table

Same answers, easier to scan:

	Flo	Clue	Stardust	Dew
Data on company servers?	Yes	Yes	Yes	No
End-to-end encrypted?	No	No	No	Yes
Third-party SDKs?	Yes	Limited	Yes	No
No-account option?	No	No	No	Yes
Subpoena-reachable?	Yes	Yes	Yes	No
Survives company shutdown?	No	Partial	No	Yes

The honest take

Clue is the best of the cloud-stored options — German jurisdiction, no ad networks, transparent about research sharing. If you want a cloud-tied tracker, that's the one.

Dew is the only one in the four where the privacy properties are structural rather than contractual. The others are trusting their company to follow its own policy. Dew can't break the policy because the architecture doesn't allow it.

Flo and Stardust are not bad apps. They have features (large communities, broader symptom libraries, partner sharing) the more-private options don't yet. If those features matter more to you than privacy, install those — just go in with eyes open about what you're trading.

For more, see the best private period tracker apps in 2026 and are period tracker apps safe?