Flo vs Clue vs Stardust: 2026 Period App Showdown

Flo, Clue, and Stardust show up together in nearly every "which period app should I download" thread right now, and the honest answer is that they're not solving the same problem. Flo is the feature-complete option with the largest community in the category. Clue is the science-first option, built in Berlin under some of the strictest data laws in the world. Stardust is the newer, design-forward option, leaning into moon phases and daily hormone narratives in a way that's made it one of the apps Gen Z talks about most on TikTok.

All three have a documented privacy record worth reading before you hand over cycle data, and the differences between them are bigger than a features list alone would suggest. We'll walk through what you get with each, then spend real time on the privacy architecture, because that's the part most comparisons skip.

---

The Short Version

If you're in a rush, here's the quick breakdown:

Want more detail? Keep reading.

---

Flo: What You Get

Flo is the most-used period tracker in the category, with around 77 million active users and over 300 million registered accounts. It's the app most of your friends probably already have, and that scale shows up in the feature list.

Features

• Cycle tracking with AI-powered predictions
• AI Health Assistant that checks in on symptoms like cramps, fatigue, and mood
• Thousands of health articles reviewed by 100+ medical professionals
• Secret Chats: anonymous community discussions, with about 7 million people chatting monthly
• Pregnancy mode with week-by-week tracking, included free
• Apple Health integration and an Apple Watch companion app

Pros

• The largest community in the category, with anonymous discussions on nearly any symptom or question
• An extensive, medically reviewed content library
• Free pregnancy mode with week-by-week updates

Cons

• Free users see ads, and the AI Health Assistant sits behind Flo Premium (~$59.99/year as of 2026)
• No nutrition, habit, or sleep tracking built in
• The privacy history (below) is the biggest thing to weigh before committing your data

Pricing

Free: Cycle and symptom tracking, pregnancy mode, community access. Includes ads.

Flo Premium: ~$12.99/month or ~$59.99/year as of 2026. Adds the AI Health Assistant, an ad-free experience, and full content library access. Check current pricing in-app, as it can shift with promotions.

Download: Available on iOS and Android

---

Clue: What You Get

Clue was founded in Berlin in 2012 and has built its identity around a science-first approach to cycle prediction. It's the tracker that scientists, researchers, and privacy advocates tend to recommend, and its algorithm has been studied in published research on menstrual cycle variability.

Features

• Cycle and symptom tracking with prediction algorithms informed by published research
• CE mark in the EU for its cycle-tracking and ovulation-prediction features, reflecting regulatory-grade validation there
• Wearable sync (Oura, Fitbit, WHOOP) with Clue Plus
• Pregnancy mode and deeper cycle insights with Clue Plus
• A clean, minimal interface with no ads

Pros

• The strongest privacy reputation of the three, with a decade-long clean track record
• A science-first build, with a CE mark reflecting regulatory validation in the EU
• Flexible, detailed symptom logging that works well for cycles that aren't textbook

Cons

• The free tier is thinner than it used to be. Pregnancy mode, wearable sync, and deeper insights are locked behind Clue Plus (~$39.99/year), and free users see frequent prompts to upgrade
• Smaller community than Flo, with less content and fewer discussion features
• No astrology or lifestyle framing if that's part of what keeps you engaged with a tracker

Pricing

Free: Basic cycle and symptom tracking.

Clue Plus: ~$39.99/year as of 2026. Adds pregnancy mode, wearable sync, and deeper cycle insights. Check current pricing in-app.

Download: Available on iOS and Android

---

Stardust: What You Get

Stardust pairs standard period tracking with moon phases, hormone-stage explanations, and a distinct visual style that's made it one of the more-discussed period apps on TikTok. It has more than 5 million downloads and a 4.76 out of 5 rating across roughly 110,000 App Store ratings.

Features

• Cycle tracking with a daily readout of where you are hormonally and what that can feel like
• Cycle syncing content that aligns your cycle with lunar phases, plus a moon calendar
• "Cycle Horoscope" and zodiac-matched content
• Cycle Recap, added in 2026, summarizing your last cycle's sleep and activity patterns by phase
• Friend syncing so you can compare cycles with people you share the app with

Pros

• Genuinely fun to open, which is a real reason people stick with a tracker instead of abandoning it after a week
• Core cycle tracking, symptom logging, and daily content are all free
• Has made real, credit-worthy changes since 2022, including dropping an overstated encryption claim and law-enforcement language

Cons

• Symptom tracking is lighter than Flo's or Clue's, and there's no pregnancy mode
• Requires an account, with no local-only option for data that stays entirely on-device
• Its privacy policy has changed twice in the last seven months as of mid-2026, each revision disclosing more ad-partner data sharing (see below)

Pricing

Free: Core cycle and symptom tracking, moon-phase and hormone content.

Stardust Plus: ~$2.99/week, ~$3.99/month, or ~$24.99/year as of 2026. Adds deeper insights, unlimited friend syncs, and additional content. Check current pricing in-app.

Download: Available on iOS and Android

---

Privacy Architecture: How Each App Actually Handles Your Data

This is the section most comparisons skip, and it's arguably the most important one. Cycle and fertility data is some of the most sensitive information you can put in an app, and "privacy" means something different for each of these three depending on where they're based, how they're regulated, and what their public record actually shows.

Flo: FTC Settlement, Then a 2025 Verdict

In 2021, the FTC settled with Flo over sharing users' health data with companies including Facebook and Google without proper consent. A related class action against Flo and Google got preliminary court approval for a combined $59.5 million settlement in April 2026, with a final approval hearing set for October 2026, and a jury separately found Meta liable in August 2025 for its role in receiving that data.

Flo has since added Anonymous Mode, which separates your health data from your identity, and open-sourced it. These are real changes, made after years of public scrutiny. Whether that history changes your decision is a personal call, and it's worth reading Flo's current privacy policy directly.

Clue: Berlin, GDPR, and a CE Mark

Clue is based in Berlin, Germany, which means it's subject to strict EU GDPR privacy laws. It has publicly committed to not sharing user data with US authorities and states it does not sell personal data. Its cycle and ovulation-prediction features also carry a CE mark in the EU, a regulatory designation tied to its science-first approach to how it builds and validates predictions. Clue has no major public enforcement actions or class actions on record.

Stardust: 2022 Criticism, Revised Since, With New Scrutiny in 2026

In 2022, reporting found that Stardust had shared users' phone numbers with a third-party analytics service, and that the app had marketed itself as "encrypted" using language that implied end-to-end encryption when its actual encryption was standard, not end-to-end. Its privacy policy at the time also stated it would comply with law enforcement requests for user data whether or not legally required to, a detail that drew attention after Roe v. Wade was overturned that year. Stardust has since made real changes: it removed the overstated encryption claim and dropped the "whether or not legally required" language, and the company says it has never actually received a law enforcement request for user data.

More recently, a Mozilla Foundation review published in July 2026 found that Stardust's privacy policy had been revised twice in roughly seven months, with each revision disclosing more device and advertising data sharing, including naming Meta's and Google's ad-measurement tools as data partners as of May 2026. Its separate Health Data Privacy Policy, unchanged since October 2025, still states that health data itself sits under a randomized ID, separated from your name or contact information. Read the current version of both policies yourself if this is a deciding factor for you.

Taken together, the three apps sit in a fairly clear order on paper: Clue has the cleanest and longest public record, Flo has the most public enforcement history balanced against real remediation, and Stardust is the newest and least tested of the three, with privacy terms that are still actively changing. None of that means any one app is "unsafe," but it's the kind of thing worth knowing before you decide where three years of period, mood, and symptom data lives.

---

The Fourth Option: Go Go Gaia

Flo, Clue, and Stardust all approach the same core job, tracking your period, from different angles: community and depth, science and privacy, or daily ritual. None of them track your mood, sleep, fitness, or nutrition alongside your cycle in real depth. Go Go Gaia takes a different approach: instead of being a cycle tracker with a few extras, it's built to track your whole health picture, cycle included, in one place.

What It Adds

• Cycle tracking with automatic phase detection and fertility predictions
• 350+ metrics across mood, sleep, fitness, and nutrition tracked alongside your cycle
• 1-click logging for fast daily tracking
• Correlation insights showing how your lifestyle connects to your cycle
• Available on iOS and as a web app
• No ads, no data selling

Pros

• Cycle, mood, sleep, fitness, and nutrition tracking in one free app
• No ads and no data selling
• Correlation insights that connect lifestyle patterns to cycle data, something none of the other three do

Cons

• iOS only. There's no Android app. A web app is available for other platforms, but the full experience is iPhone-only right now.
• No community, no moon-phase content. It doesn't try to be either Flo's discussion forums or Stardust's daily astrology narrative.
• Smaller, newer app. It doesn't have Flo's 77 million active users, Clue's decade-plus track record, or Stardust's TikTok-driven following. Fewer reviews, a shorter history.
• AI features are premium. Advanced insights require a subscription (~$9.99/month or ~$49.99/year).

Pricing

Free: Cycle, mood, sleep, fitness, and nutrition tracking. No ads.

Premium: ~$9.99/month or ~$49.99/year for AI features and advanced insights.

Download: Available on iOS App Store

---

Which Should You Choose?

There's no single "best" app here. It comes down to what actually gets you to open a tracker consistently, and what you're comfortable with on the privacy side. Here's the honest breakdown of when each is the better pick:

---

Frequently Asked Questions

How do Flo, Clue, and Stardust compare?

All three track your cycle, but they're built around different priorities. Flo has the largest community and the deepest content library (Flo Premium about $59.99/year). Clue is a Berlin-based, CE-marked app built on a science-first approach with a strong privacy reputation (Clue Plus about $39.99/year). Stardust wraps cycle tracking in moon-phase and astrology content aimed at making tracking feel like a daily ritual (Stardust Plus about $24.99/year). None of the three are birth control. Which one fits depends on whether you want community and depth, science and privacy, or a tracker that feels fun to open.

Which is best for privacy: Flo, Clue, or Stardust?

Clue has the strongest privacy reputation of the three. It's based in Berlin, Germany, subject to strict EU GDPR rules, and CE-marked as a medical device, with a clean public record. Flo settled with the FTC in 2021 over sharing health data with Facebook and Google. A related class action against Flo and Google got preliminary court approval for a combined $59.5 million settlement in April 2026, with a final approval hearing set for October 2026, and a jury separately found Meta liable in August 2025. Flo has since added Anonymous Mode. Stardust drew criticism in 2022 for sharing phone numbers with a third-party analytics service and overstating its encryption. It has since revised its practices, but a Mozilla Foundation review in July 2026 found its privacy policy had been revised twice in about seven months, disclosing more ad-partner data sharing, including with Meta's and Google's ad-measurement tools as of May 2026. Read each company's current privacy policy before you decide.

Which app has the best free version: Flo, Clue, or Stardust?

All three have usable free tiers, but they differ in what's included. Flo's free tier includes pregnancy mode but shows ads. Clue's free tier covers basic cycle and symptom logging, but pregnancy mode, wearable sync, and deeper insights sit behind Clue Plus. Stardust's core cycle tracking and daily content are free, with deeper insights and unlimited friend syncing behind Stardust Plus. If a fully free experience with pregnancy tracking matters most, Flo has the edge. If ad-free basic tracking matters more, Clue or Stardust may fit better.

Is Clue a medical device?

Clue carries a CE mark in the EU for its cycle-tracking and ovulation-prediction features, which means it meets certain regulatory standards for a software medical device there. That's different from being FDA-cleared as birth control in the US, which Clue is not, and its own app guidance says not to use it as contraception. The CE mark reflects Clue's science-first approach to how it builds and validates its predictions, not a claim that it prevents pregnancy.

What happened with Stardust's privacy policy in 2026?

A Mozilla Foundation review published in July 2026 found that Stardust's privacy policy had been revised twice in roughly seven months, with each revision disclosing more device and advertising data sharing, including naming Meta's and Google's ad-measurement tools as data partners as of May 2026. This came after Stardust's 2022 criticism over sharing phone numbers with a third-party analytics service and overstating its encryption, both of which the company addressed at the time. Stardust's separate Health Data Privacy Policy, unchanged since October 2025, still states health data sits under a randomized ID separated from your name or contact information. Read the current version of both policies yourself before logging sensitive symptoms.

What's a good alternative to Flo, Clue, and Stardust?

Go Go Gaia is worth a look if you want cycle tracking folded into a broader health picture, tracking 350+ metrics across mood, sleep, fitness, and nutrition with 1-click logging and correlation insights showing how your lifestyle connects to your cycle. Core features are free with no ads. The tradeoffs are that it's iOS only (a web app covers other platforms), doesn't have Flo's community or Stardust's daily content, and is a newer, smaller app than any of the three.

Can you use Flo, Clue, or Stardust as birth control?

Flo, Clue, and Stardust are all period and cycle trackers, and none of them are cleared by the FDA to prevent pregnancy. Clue's own app guidance states it should not be used as a contraceptive, and neither Flo nor Stardust markets itself as one. If app-based birth control is what you're after, that's a distinct category of app (Natural Cycles is the FDA-cleared example) and a conversation to have with a healthcare provider.

---

Want the Deeper Head-to-Head?

This guide covers all three at once, with a focus on the privacy side. If you're weighing two of them specifically, or want a different third brand in the mix, these go further.

• Clue vs Flo vs Natural Cycles: 2026 Comparison →
• Flo vs Stardust: Which Period Tracker Fits You? →
• Clue vs Flo: Which Period Tracker Is Actually Better? →

Related Articles

• Flo Alternatives 2026: 7 Period Trackers Compared
• How Accurate Are Period Tracker Apps, Really?
• Best Period Tracker App 2026: Clue vs Flo vs Ovia (6 Apps Compared)

Other App Comparisons

• Flo vs Natural Cycles: Which One Should You Use?
• Clue vs Natural Cycles: Which One Should You Use?
• Flo vs Go Go Gaia: Which One Should You Use?
• Best Cycle Syncing Apps 2026: 28 vs Stardust vs MyFlo vs Flo