Period tracking apps collect some of the most intimate health data on your phone. Cycle dates, symptoms, sexual activity, mood, pregnancy attempts, and medical conditions -- all logged voluntarily by users who trust the app to handle that information responsibly. In 2026, after years of privacy scandals and regulatory actions, choosing a period tracker is as much a privacy decision as a feature decision.
This comparison looks at three popular period trackers -- Cyla, Flo, and Clue -- through the lens of privacy, features, and pricing. All three have genuine strengths. The question is which one's approach to your data aligns with your expectations.
Period tracker data is uniquely sensitive for several reasons. It can reveal whether someone is pregnant, trying to conceive, or has had a pregnancy loss. In jurisdictions where reproductive healthcare is legally restricted, this data has potential legal implications. Even in countries with strong privacy protections, a data breach exposing cycle tracking information is fundamentally different from a breach exposing, say, weather app data.
This is not theoretical. In January 2023, the US Federal Trade Commission (FTC) took action against Flo Health, the maker of the Flo period tracker, for sharing users' health data with third parties including Facebook and Google after promising to keep it private. The FTC's complaint alleged that Flo disclosed sensitive health information to analytics and marketing companies without users' consent, contradicting its own privacy policy.
Flo settled with the FTC, agreed to obtain independent privacy reviews, and introduced an "Anonymous Mode" feature. The company has made genuine efforts to improve its privacy practices since then. But the case demonstrated that even popular, well-funded health apps can mishandle intimate data -- and that privacy policies are only as reliable as the companies behind them.
Flo is the most downloaded period tracker in the world, with over 380 million downloads. Its popularity is deserved. The app is polished, feature-rich, and backed by a large team of developers and medical advisors. It offers cycle tracking, ovulation predictions, pregnancy mode, symptom logging, health insights, and a content library with articles reviewed by medical professionals.
Flo's AI assistant can answer health questions, and the app provides personalised insights based on your logged data. The community features let users share experiences and ask questions anonymously. For breadth of features and content, Flo is difficult to match.
Following the 2023 FTC settlement, Flo introduced Anonymous Mode, which allows users to use the app without associating data with their name, email, or other identifying information. This was a direct response to user concerns about data subpoenas and legal risks.
However, even with Anonymous Mode, Flo's architecture is cloud-based. Your cycle data is stored on Flo's servers, not solely on your device. The company states that data is encrypted and protected, but the fundamental model means your health data exists on infrastructure controlled by a third party. Flo's updated privacy policy is more transparent than before, and the company is subject to ongoing FTC oversight, which provides an additional layer of accountability.
Flo uses a subscription model. The free tier provides basic tracking. Flo Premium (approximately $9.99/month or $49.99/year) unlocks AI insights, advanced health reports, and personalised content. Over three years, the subscription costs roughly $150.
Clue positions itself as the scientific period tracker. Developed by a Berlin-based team, the app emphasises evidence-based predictions and collaborates with academic researchers. Clue has partnered with institutions including Oxford, Stanford, and Columbia University on menstrual health research, and it publishes research papers based on (anonymised, aggregated) user data.
The app's design is clean and data-focused. It tracks over 30 cycle-related categories, provides cycle predictions based on your personal history, and offers educational content grounded in peer-reviewed research. Clue avoids the overly pink, flower-themed aesthetic common in period trackers, opting instead for a neutral, clinical design that many users prefer.
Clue stores data on its servers, but the company has been vocal about privacy, particularly since the Dobbs decision in the US. Clue published a public statement in 2022 committing to protecting user data and noting that as a European company, it is subject to GDPR, which provides stronger privacy protections than US law.
Clue's research partnerships mean that some aggregated, anonymised data is shared with academic institutions. The company states that individual-level data is not shared, and that research data is stripped of identifying information. For users who support menstrual health research, this is a positive. For users who want zero data sharing of any kind, it is a consideration.
Clue Plus (the subscription tier) costs approximately $9.99/month or $39.99/year. The free tier remains functional for basic tracking, but advanced analysis and predictions are locked behind the subscription.
Cyla takes a fundamentally different architectural approach. All cycle data is stored on-device. There is no account creation, no cloud storage, no server infrastructure holding your health data. The app does not know who you are, where you are, or what you are tracking. Your data is encrypted by iOS on your device, and it never leaves your phone.
Feature-wise, Cyla provides cycle tracking, symptom logging, predictions, Apple Watch integration with wrist temperature data, and Apple Health synchronisation. It does not have the content library, community features, or AI assistant that Flo offers. It is a focused tracking tool rather than a comprehensive health platform.
Cyla uses a one-time purchase model. You pay once and own the app. There is no subscription, no premium tier, and no feature gating.
| Feature | Flo | Clue | Cyla |
|---|---|---|---|
| Data storage | Cloud (Flo servers) | Cloud (Clue servers, EU) | On-device only |
| Account required | Yes (Anonymous Mode available) | Yes | No |
| Data shared with third parties | Post-FTC: restricted | Anonymised research data | No |
| Jurisdiction | US (FTC oversight) | EU (GDPR) | N/A (no server) |
| Subpoena risk | Data exists on servers | Data exists on servers | No server-side data |
| Encryption | In transit and at rest | In transit and at rest | iOS device encryption |
| FTC action history | Yes (2023) | No | No |
Privacy is not the only consideration. Features matter too, and there are genuine trade-offs:
| Feature | Flo | Clue | Cyla |
|---|---|---|---|
| Cycle tracking | Yes | Yes | Yes |
| Symptom logging | Extensive | 30+ categories | Yes |
| Ovulation prediction | Yes | Yes | Yes |
| Pregnancy mode | Yes | Yes | No |
| AI health assistant | Yes (premium) | No | No |
| Apple Watch temperature | Limited | No | Yes |
| Community features | Yes | No | No |
| Health content library | Extensive | Good (evidence-based) | No |
| Research partnerships | Some | Extensive (Oxford, Stanford) | No |
| Apple Health sync | Yes | Yes | Yes |
| Pricing | Free / ~$49.99/year | Free / ~$39.99/year | One-time purchase |
The privacy table above shows the differences on paper. Here is what they mean in practice for each app:
Flo: Your cycle data lives on Flo's servers. If Flo is breached (which has happened -- the 2023 FTC action arose from data being shared with Facebook and Google), your data is exposed. If law enforcement issues a subpoena to Flo, they can hand over your records. Anonymous Mode removes your name and email from the data, but the cycle data itself still sits on infrastructure Flo controls. The improvement since the FTC settlement is real, but the underlying exposure remains: your health data exists somewhere other than your phone.
Clue: Your data is on Clue's EU-based servers, which means GDPR applies. In practice, this gives you the right to request deletion, the right to export, and subjects Clue to stricter breach notification requirements than US companies face. However, GDPR does not prevent law enforcement access -- it regulates it. If a German or EU court orders Clue to produce records, they must comply. The EU framework is meaningfully stronger than the US one, but it is still a policy framework, not a technical barrier.
Cyla: There is no server. Your cycle data is stored in the iOS sandbox on your device, encrypted by the hardware. A breach of Cyla's infrastructure is impossible because there is no infrastructure to breach. A subpoena to the developer would produce nothing, because they do not possess your data. The trade-off is concrete: no cross-device sync, no account recovery if you lose your phone, no community features. You get privacy through absence rather than through policy.
You want the most feature-rich period tracker available. Flo's AI assistant, community features, pregnancy mode, and health content library are unmatched in scope. If you value these features and are comfortable with cloud-based data storage (particularly with the improved privacy protections following the FTC settlement), Flo provides the most comprehensive experience. The Anonymous Mode option adds a layer of protection that did not exist before 2023.
You value evidence-based, science-first design and want your data subject to EU privacy law. Clue's academic partnerships and research-grounded approach appeal to users who want their tracker to be informed by peer-reviewed science rather than trending health content. Clue's GDPR protections are meaningfully stronger than US privacy law, which matters if regulatory framework is important to you. The design is also notably gender-neutral, which some users strongly prefer.
Privacy is your primary criterion and you want the certainty that comes from on-device architecture rather than server-side promises. Cyla does fewer things than Flo or Clue, but what it does, it does without creating any external copy of your health data. The one-time purchase model also means no ongoing cost. If you want a focused tracker that handles the core use case -- tracking your cycle privately -- without the broader health platform features, Cyla is the most private option available.
The period tracker market in 2026 reflects a broader tension in consumer technology: features vs privacy. Cloud-based apps can offer richer experiences because they have access to your data on their infrastructure. On-device apps are more limited in features but offer stronger privacy guarantees. Neither approach is inherently wrong.
What matters is that you make the choice deliberately. Read the privacy policy. Understand where your data is stored. Consider what would happen if the company were acquired, breached, or served with a legal order. Your cycle data is yours. Make sure it stays where you want it.