Clue is the better choice if you prioritize science-backed design, privacy, and a no-nonsense interface. Flo is the better choice if you want deeper integration with Apple Health and a more guided, content-rich experience. Both apps are free to use for basic period tracking, and both charge about $40 per year for premium features. The real differences come down to design philosophy, data privacy track records, and a few standout features unique to each app.
Design and Interface
The two apps feel noticeably different from the moment you open them. Flo leans into a lifestyle approach with articles, tips, and a conversational tone. It asks onboarding questions right away about your last period and typical cycle length, then serves up a feed of health content tailored to where you are in your cycle. The experience is visually warm and magazine-like.
Clue takes the opposite approach. Its design team built the app around three priorities: fast data entry, user satisfaction, and accurate insights. The interface is minimal, using a circular calendar view to visualize your cycle. Clue deliberately avoids euphemisms and cutesy language. Bleeding is called “bleeding,” not a nickname. The app uses gender-neutral terminology throughout, making it more inclusive for trans and nonbinary users who menstruate. If you find pink-themed, flower-laden period apps annoying, Clue will feel like a relief.
Tracking and Free Features
Both apps let you log periods, symptoms, moods, and other daily data for free. Clue’s free version is notably generous: it shows symptom patterns across your cycle, estimates your fertility window, and flags irregularities in your predicted cycle. You get a useful overview without paying anything.
Flo’s free tier covers the basics of period and ovulation prediction but gates more detailed insights behind its premium subscription. Where Flo pulls ahead is in ecosystem integration. Flo syncs every logged symptom to Apple Health and pulls in data from sleep and exercise apps, so you can see how your cycle intersects with the rest of your health data. Clue only syncs period dates to Apple Health. If you already track sleep, workouts, or other metrics on your phone, that difference matters.
Medical Credibility
This is where Clue has a clear edge. Clue includes over 100 pages of health content drawn from peer-reviewed research, and its text is reviewed by doctors and gynecologists. More significantly, Clue’s birth control feature received FDA clearance as a Class II medical device. The algorithm uses period start dates to predict high-risk and low-risk days for pregnancy, functioning as a fertility awareness-based method of contraception. In clinical testing, its perfect-use pregnancy rate was 0.8 per 100 women per year, and its typical-use rate was 5.2 per 100 women per year. That makes it a legitimate, regulated contraceptive option for women aged 18 to 45 with predictable cycles between 20 and 40 days. No other mainstream period tracker has this level of regulatory validation.
Both apps have introduced PCOS screening tools that evaluate your risk for polycystic ovary syndrome based on logged symptoms. These tools are useful conversation starters with a doctor, but they cast a wide net. When Flo rolled out its health assessments, about 38 percent of the 636,000 women who completed them in a single month were told to ask their doctor about PCOS, a rate that raised questions among clinicians about over-flagging.
Privacy and Data Security
Privacy is a major concern for period tracking apps, especially in the post-Dobbs legal landscape. Both Flo and Clue are headquartered in the European Union (Flo in London, Clue in Berlin), and both comply with GDPR, which sets a higher bar for data protection than U.S. law. Both apps allow local data storage with user consent, and both share data with third parties, also with consent.
Their histories diverge, though. Flo was investigated by the FTC for sharing user data with third parties like Facebook and Google between 2016 and 2019. Flo said the shared data was for measuring app performance and didn’t include sensitive health information, but the company ended the practice and settled with the FTC in 2021. Since then, Flo has taken visible steps to rebuild trust. It launched Anonymous Mode, which lets you use the app without your name, email, or technical identifiers (including your IP address) being linked to your health data. Flo also became the first period tracker to earn ISO 27001 certification, an international standard for information security management, completing four audits to get there.
Clue has no comparable regulatory history. The company has explicitly stated it will not share user data with the U.S. government. Clue hasn’t pursued the same kind of third-party security certification that Flo has, but it also hasn’t had a data-sharing scandal to recover from. For some users, a clean record matters more than a certification earned after a breach of trust.
Pricing
The premium tiers are priced similarly. Flo Premium costs $39.99 per year or $11.49 per month. Clue Plus costs $39.99 per year or $9.99 per month. If you pay monthly, Clue is slightly cheaper. Annually, they’re identical. The free versions of both apps handle basic period tracking perfectly well, so you may not need to pay at all unless you want detailed cycle analysis, personalized insights, or (in Clue’s case) the birth control feature.
Which App Fits You
Choose Clue if you want a straightforward, science-first tracker with gender-neutral language, a strong free tier, and the option to use an FDA-cleared birth control feature. Clue is also the safer bet if data privacy is your top concern and you’d rather avoid an app with a history of FTC scrutiny.
Choose Flo if you want an app that connects to your broader health ecosystem through Apple Health, serves up daily wellness content, and offers a more guided experience. Flo’s Anonymous Mode and ISO 27001 certification show genuine investment in security, even if they came as a course correction. If you like having sleep data, exercise stats, and cycle insights in one place, Flo does that better than Clue.
Both apps predict periods and ovulation reliably for people with regular cycles. Neither is a bad choice. The decision comes down to whether you prefer Clue’s clinical minimalism or Flo’s content-rich, connected approach.