TLDR
Natural Cycles and Clue both have cleaner privacy records than Flo. Natural Cycles has FDA De Novo clearance and no documented violations. Clue is GDPR-compliant in Berlin. Both still store data server-side, which means both can receive subpoenas. If you want no server component at all, neither is the answer.
| Factor | Natural Cycles | Clue | Floriva |
|---|---|---|---|
| Data location | NC servers | Clue servers | Your device |
| Account required | Yes | Yes | No |
| Regulatory oversight | FDA De Novo | GDPR (Berlin) | N/A |
| Documented violations | None | None | None |
| Subpoenable | Yes | Yes | No |
| Free tier | No | Yes | 14-day trial |
| Monthly cost | $12.99 | Free / $9.99 | $2.99 |
| Contraceptive efficacy | FDA-cleared | No clearance | No clearance |
- On-device storage
- A storage model where data is saved locally to the user's phone or tablet and never transmitted to a remote server. There is no company-held copy of the data, which means no subpoena surface and no breach exposure from company servers.
DEFINITION
- Zero-knowledge storage
- A data storage model where the service provider holds only encrypted data they cannot read. The encryption keys never leave the user's device. Even if the company is subpoenaed, they can only produce ciphertext that is useless without the user's key.
DEFINITION
Two Apps, Two Different Jobs
Natural Cycles and Clue occupy different positions in the period tracker category. Natural Cycles is built specifically for fertility awareness as a contraceptive method. The FDA clearance it holds is for that purpose: as a contraceptive decision support tool. Clue is a comprehensive cycle and health tracker. It covers periods, fertile windows, birth control reminders, mood, symptoms, and research-backed health analysis. It does not claim contraceptive clearance.
Accuracy and the Temperature Requirement
Natural Cycles’ contraceptive effectiveness depends on daily basal body temperature tracking. BBT rises slightly after ovulation, providing a retrospective signal for fertility prediction. The algorithm combines this with cycle history. Typical-use effectiveness is 93%, functional as a method, but lower than hormonal contraception.
Clue predicts cycles and fertile windows without requiring temperature input. It uses historical cycle data, symptoms, and logged health information. For general cycle awareness, this is sufficient. For contraceptive decisions, the lack of FDA clearance means it is not in the same category as Natural Cycles.
Two Apps Without Flo’s Problems
Users evaluating period trackers after the Flo FTC settlement often land on Natural Cycles or Clue as the next tier of consideration. Both have things Flo lacks: a cleaner privacy record, no documented enforcement actions, and no history of sharing data with advertising platforms.
The comparison between them is genuinely close on most dimensions. What separates them is regulatory framework, price, and purpose.
Natural Cycles: FDA Oversight as Accountability
Natural Cycles received FDA De Novo clearance in 2018, making it the first app-based contraceptive method cleared by the FDA. This clearance required Natural Cycles to demonstrate contraceptive efficacy through clinical trials and to submit to ongoing regulatory oversight.
What FDA clearance means for privacy is indirect. The FDA oversight creates organizational accountability and a compliance culture. A regulated medical device company faces higher reputational and legal risk from data misuse than an unregulated app. Natural Cycles operates under GDPR from Sweden, adding European data protection regulations.
None of this prevents a subpoena. The regulatory oversight is real but it is about contraceptive efficacy, not about your data’s legal accessibility.
Clue: GDPR in Practice
Clue’s Berlin headquarters means it operates under GDPR, which provides substantive protections beyond what US law offers. GDPR limits how Clue can use your data commercially, requires meaningful consent for data processing, gives you access and deletion rights, and restricts transfers to inadequate jurisdictions. Clue also runs no advertising business, removing the commercial incentive to monetize user data.
GDPR’s limitation is the same one that applies to Natural Cycles’ regulatory framework: it limits commercial data practices, not responses to valid legal orders. A court with jurisdiction can override GDPR in specific legal proceedings.
Price and Use Case
The most practical distinction between Natural Cycles and Clue is price and use case. Natural Cycles costs $12.99/mo with no free tier. If you are not using it as a contraceptive method, the price is hard to defend. Clue offers a functional free tier with core tracking features and costs $9.99/mo for the full feature set.
For users who are evaluating period trackers primarily for cycle tracking rather than fertility-based contraception, Clue is the more cost-effective cloud-based option. For users who want on-device storage without paying Natural Cycles’ price, Floriva is $2.99/mo with no server component.
Neither feels private enough?
The Floriva app stores everything on your device. No data sold, no account required.
See plans & pricingVerdict
Both Natural Cycles and Clue are defensible choices for users coming from Flo. Natural Cycles adds regulatory accountability through FDA oversight; Clue adds a free tier and science-backed features. The shared limitation is server-side storage. For users whose concern is legal data exposure rather than commercial privacy practices, neither solves the structural problem.
PROS & CONS
Natural Cycles
Pros
- FDA clearance adds regulatory accountability
- No documented data violations
- Temperature-based precision
Cons
- Most expensive, no free tier
- Server-based
- FDA clearance is for efficacy, not privacy
PROS & CONS
Clue
Pros
- GDPR jurisdiction
- No-ads model
- Free tier available
Cons
- Server-based
- Account required
- GDPR limits commercial use, not legal process
PROS & CONS
Floriva
Pros
- On-device storage
- No account
- Not subpoenable
- $2.99/mo
Cons
- No FDA clearance
- No free tier (14-day trial)
Q&A
Is Natural Cycles FDA approved as birth control?
Natural Cycles received FDA De Novo clearance in August 2018 as a contraceptive app, the first digital contraceptive to receive this designation in the US. De Novo is a regulatory pathway for novel medical devices. Typical-use effectiveness is approximately 93%, which is lower than hormonal methods but higher than barrier methods used alone. It requires consistent daily basal body temperature tracking.
Q&A
Is Natural Cycles safer than Clue for data privacy?
The two are comparable in terms of documented privacy history. Neither has enforcement actions or known data-selling incidents. Natural Cycles has the additional accountability of FDA De Novo clearance, which subjects it to regulatory oversight, though that oversight covers contraceptive efficacy rather than privacy practices specifically. Both are server-based, so both can be subpoenaed. The choice between them on pure privacy grounds is close.
Q&A
Which is more accurate for cycle tracking, Natural Cycles or Clue?
Natural Cycles uses basal body temperature as its primary input and is specifically validated for fertility awareness as a contraceptive method. Clue uses cycle history, symptoms, and health data to predict cycles and fertile windows without requiring temperature tracking. For contraceptive decision-making, Natural Cycles has the clinical validation and FDA clearance. For general cycle prediction without daily temperature measurement, Clue's algorithm is well-regarded.
Q&A
Do either Natural Cycles or Clue sell period data?
Neither has a documented history of selling user data to advertisers or data brokers. Clue operates on a subscription model with no advertising. Natural Cycles is a regulated medical device with no advertising component. Both are meaningfully different from Flo's documented ad-supported data sharing model.
Source: Natural Cycles pricing
Source: Clue pricing page
Source: Reuters / FTC, September 2025
Frequently asked