TLDR
The best period tracker depends on how much you value privacy architecture over feature count. On-device apps (Floriva, Euki, Drip) never send data to a server, making them structurally safer post-Dobbs. Server-based apps (Clue, Natural Cycles, Flo) offer larger datasets and more features but create subpoenable records. Flo carries documented FTC enforcement history and a $59.5M settlement.
| App | Data Architecture | Enforcement History | Platform | Price |
|---|---|---|---|---|
| Floriva | On-device + encrypted sync | None | iOS + Android | $2.99/mo |
| Clue | Server-based (GDPR) | None | iOS + Android | Free / $9.99/mo |
| Euki | On-device | None | iOS + Android | Free |
| Drip | On-device (open source) | None | Android only | Free |
| Natural Cycles | Server-based (FDA-cleared) | None | iOS + Android | $12.99/mo |
| Flo | Server-based | FTC 2021; $59.5M settlement 2025 | iOS + Android | Free / Premium |
| Stardust | Cloud-based | None | iOS + Android | Free |
| Glow | Cloud-based | None | iOS + Android | Free / Premium |
Floriva
On-device storage with cross-device encrypted sync. iOS and Android. No mandatory account. No third-party advertising SDKs.
Pros
- ✓ Data stored on-device — no server to subpoena
- ✓ Cross-device encrypted sync for users who opt in
- ✓ No account required to track
- ✓ No third-party advertising SDKs
Cons
- × Paid subscription after 14-day trial
- × Newer app with smaller prediction dataset than established competitors
Pricing: $2.99/mo or $24.99/yr (14-day free trial)
Verdict: Strongest privacy posture with cross-platform support. The only on-device tracker offering encrypted sync across devices.
Clue
Berlin-based, GDPR-compliant, no advertising business model. Server-based. Scientific advisory board with evidence-based cycle science.
Pros
- ✓ GDPR compliance under EU law — stronger than US standards
- ✓ No ad-funded model
- ✓ Scientific advisory board and evidence-based predictions
- ✓ iOS and Android
Cons
- × Server-based — data exists on Clue's servers and can be subpoenaed
- × Requires account
- × $9.99/mo for full features
Pricing: Free tier / $9.99/mo
Verdict: Best privacy among server-based apps. GDPR jurisdiction and no-ads model are real advantages, but server-side data remains accessible via legal process.
Euki
Built by nonprofit Ibis Reproductive Health. On-device storage, no accounts, no data collection. Free. iOS and Android.
Pros
- ✓ Nonprofit developer with no commercial incentive to monetize data
- ✓ On-device storage
- ✓ No account or email required
- ✓ Free, no ads
Cons
- × No cross-device sync
- × Fewer prediction and symptom logging features than funded apps
- × Less active development
Pricing: Free
Verdict: Best free on-device tracker. Nonprofit structure and on-device storage together remove both the structural and incentive paths to data monetization.
Drip
Open source period tracker. Android only. No accounts, no server, no analytics. Source code publicly auditable.
Pros
- ✓ Open source — privacy claims independently verifiable
- ✓ No accounts, no analytics, no server
- ✓ Free
Cons
- × Android only — no iOS version
- × Basic feature set
- × No cross-device sync
Pricing: Free
Verdict: Best for Android users who want verified-not-promised privacy. Open source with on-device storage is the strongest transparency combination available.
Natural Cycles
FDA De Novo clearance for contraception (2018). Temperature-based tracking with subscription model. Server-based.
Pros
- ✓ FDA clearance creates regulatory accountability
- ✓ Temperature-based method adds precision beyond calendar prediction
- ✓ No documented data-sharing with advertisers
Cons
- × Server-based storage
- × Most expensive mainstream option at $12.99/mo
- × FDA clearance is for efficacy, not privacy
Pricing: $12.99/mo or $99.99/yr
Verdict: Solid for users prioritizing contraceptive accuracy over privacy architecture. FDA oversight adds accountability, but the server-based model is a privacy trade-off.
Flo
Largest user base. FTC enforcement action in 2021 for sharing data with Facebook and Google. $59.5M combined settlement in 2025. Server-based with paid Anonymous Mode.
Pros
- ✓ Large prediction dataset from extensive user base
- ✓ Full-featured symptom and cycle tracking
- ✓ Anonymous Mode available (paid)
- ✓ iOS and Android
Cons
- × FTC enforcement action for sharing health data with Facebook and Google (2021)
- × $59.5M combined settlement (Flurry $3.5M + Google+Flo $56M)
- × Anonymous Mode requires paid subscription — basic privacy costs extra
Pricing: Free tier / Premium subscription
Verdict: The documented enforcement history sets Flo apart from every other app on this list. Anonymous Mode is a policy fix on top of an unchanged cloud architecture. Server-side data remains subpoenable.
Stardust
Astrology-themed period tracker. Cloud-based. Marketing-level privacy claims without documented technical architecture.
Pros
- ✓ Free
- ✓ Social features and community angle
- ✓ iOS and Android
Cons
- × Cloud-based with no published privacy architecture details
- × Privacy claims are marketing-level — no third-party audit or open source
- × No documented on-device storage option
Pricing: Free
Verdict: Community features attract users, but unverified privacy claims are not a substitute for documented architecture. No enforcement history, but also no transparency.
Glow
Cloud-based period and fertility tracker with premium features. No documented privacy architecture or third-party audit.
Pros
- ✓ Full-featured fertility and pregnancy tracking
- ✓ Community forums
- ✓ iOS and Android
Cons
- × Cloud-based — data stored on Glow's servers
- × No documented privacy architecture
- × Premium features behind paywall
Pricing: Free tier / Premium subscription
Verdict: Feature-rich but privacy-opaque. No enforcement history, but no published privacy architecture either. Server-based by default.
How to Evaluate a Period Tracker
Where your data lives matters more than feature count.
There are two architectures: on-device (data stays on your phone) and server-based (data is stored on the company’s servers). This distinction determines whether your reproductive health data can be shared, breached, or subpoenaed.
The FTC’s enforcement actions against Flo (2021) and Premom (2023) both involved server-based apps that shared data with third parties. On-device storage cannot be shared because no company server holds a copy.
Source: FTC vs. Flo, January 2021; FTC vs. Premom, May 2023
The Ranking Criteria
This list ranks apps by:
- Data architecture — on-device vs. server-based
- Enforcement history — documented regulatory actions or settlements
- Transparency — open source, published architecture, third-party audits
- Features — cycle prediction, symptom tracking, sync, platform support
- Pricing — what you pay and what’s behind a paywall
Privacy architecture carries the most weight. A feature-rich app that stores data on servers you can’t control still creates subpoenable records.
On-Device Apps
On-device trackers store data locally on your phone. No company server holds a copy. This means no database to breach, no server to subpoena, and no possibility of undisclosed data sharing.
Consumer Reports recommended on-device trackers — specifically Drip, Euki, and Periodical — as apps that “store data locally and don’t allow third-party tracking.”
Source: Consumer Reports, August 2022
Server-Based Apps
Server-based apps store your data on company infrastructure. This enables features like automatic backup and multi-device access but creates a permanent record that can be accessed through legal process, data breaches, or policy failures.
GDPR-compliant apps like Clue offer stronger protections than US-based apps, but GDPR does not prevent lawful data requests from courts. The protection is relative, not absolute.
The FTC Precedent
Two period/fertility tracker apps have faced FTC enforcement: Flo (2021) and Premom (2023). Both were server-based. Both shared data with third parties despite privacy policy claims to the contrary.
Flo’s case resulted in a $59.5M combined settlement in 2025. The Bureau of Investigative Journalism reported that after the Dobbs ruling, Meta “was caught eavesdropping on a period app” through the Facebook SDK embedded in Flo.
Source: TBIJ, September 2025
Privacy policies can be violated. On-device architecture removes the mechanism for violation entirely.
Q&A
Is Floriva good for privacy?
Floriva uses on-device storage — your cycle data stays on your phone and is never transmitted to company servers. It is the only on-device tracker that also offers cross-device encrypted sync. No third-party advertising SDKs. No mandatory account. The architecture eliminates the structural possibility of data selling or server-side subpoena.
Q&A
Is Clue good for privacy?
Clue is the strongest option among server-based apps. It operates under GDPR (EU law with stricter privacy protections than US standards), has no advertising business model, and has no documented enforcement actions. However, it is server-based. Data on Clue's servers can be accessed via legal process. For users in US states with abortion restrictions, this is a meaningful risk factor.
Q&A
Is Euki good for privacy?
Euki is built by nonprofit Ibis Reproductive Health. It uses on-device storage, requires no account, and collects no data. The nonprofit structure removes the commercial incentive to monetize user data. The trade-off is fewer features and no cross-device sync.
Q&A
Is Drip good for privacy?
Drip is the most transparent period tracker available. It is open source (code publicly auditable), uses on-device storage, and has no server, no accounts, and no analytics. Consumer Reports recommended Drip as one of three apps that 'store data locally and don't allow third-party tracking.' The limitation is Android-only with a basic feature set.
Q&A
Is Natural Cycles good for privacy?
Natural Cycles has no documented data-sharing incidents and benefits from FDA regulatory oversight. However, FDA clearance is for contraceptive efficacy, not privacy. The app uses server-based storage, meaning data can be subpoenaed. It is the most expensive option at $12.99/mo.
Q&A
Is Flo good for privacy?
No. Flo is the only app on this list with documented FTC enforcement action for sharing user health data. The FTC found Flo shared period dates, pregnancy status, and symptoms with Facebook and Google without consent. A $59.5M combined settlement followed in 2025. Flo launched Anonymous Mode after the FTC action, but it requires a paid subscription and doesn't change the server-based architecture.
Q&A
Is Stardust good for privacy?
Stardust makes marketing-level privacy claims but has not published technical architecture details, open-sourced its code, or undergone a documented third-party audit. Cloud-based storage means data resides on Stardust's servers. Without verifiable documentation, privacy claims cannot be independently confirmed.
Q&A
Is Glow good for privacy?
Glow has no documented privacy architecture and no third-party audit. It uses cloud-based storage. No enforcement actions are on record, but the absence of documented architecture means users are relying on trust rather than verification.
Source: Reuters / FTC, September 2025
Source: Clue pricing page
Source: Natural Cycles pricing
Source: Floriva pricing
Track your cycle. Not your data.
- Plan-first pricing
- No account required
- Data never leaves your device
Pick a plan to see pricing details and next steps.
Frequently asked