Flo vs Clue vs Stardust: 2026 Period App Showdown

Flo, Clue, and Stardust show up together in a lot of "which period app should I download" threads right now, and the honest answer is that they're not solving the same problem. Flo is the feature-complete option, with over 570 million downloads according to its App Store listing. Clue is the science-first option, built in Berlin under EU data law. 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.

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The Short Version

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

Want more detail? Keep reading.

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What do you get with Flo?

Flo is one of the most widely downloaded period trackers, with over 570 million downloads worldwide according to its App Store listing (as of October 2026). It may well be on your friends' phones already, and that scale shows up in the feature list.

Features

• Cycle tracking with AI-powered predictions
• A Premium virtual Health Assistant that checks in on symptoms like cramps, fatigue, and mood
• A health article library reviewed by medical experts, per Flo
• Secret Chats: anonymous community discussions (listed as a Premium feature on the App Store)
• Pregnancy mode with week-by-week updates (in-depth pregnancy features are Premium)
• Apple Health integration and an Apple Watch companion app

Pros

• A big community, with anonymous discussions on many symptoms and questions
• An extensive content library that Flo says is reviewed by medical experts
• Pregnancy mode with week-by-week updates (in-depth features are Premium)

Cons

• Some features, including the virtual Health Assistant, sit behind Flo Premium (annual plans are listed at $47.99–$59.99 in the US App Store as of October 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: Core cycle and symptom tracking; some features sit behind Premium.

Flo Premium: annual plans are listed at $47.99 and $59.99 in the US App Store (as of October 2026). Adds the virtual Health Assistant, expert-led videos and more, per its App Store listing. Check current pricing in-app, as it can shift with promotions.

Download: Available on iOS and Android

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What do you get with Clue?

Clue is made by BioWink GmbH in Berlin and has built its identity around a science-first approach to cycle prediction. A 2016 Obstetrics & Gynecology study that scored 20 accurate, free cycle apps gave Clue the top score (13 of 15). Its App Store listing shows a 4.8 out of 5 rating from about 405K ratings (as of October 2026).

Features

• Cycle and symptom tracking with ovulation and fertile-window predictions and a "clinically validated algorithm" claim (per its App Store listing)
• Modes for period tracking, trying to conceive, pregnancy, and perimenopause
• Connects to Apple Watch, Oura, WHOOP, Withings, Fitbit and more (per its App Store listing)
• Clue Plus adds deeper analysis, advanced predictions, and personalized insights
• Tracking for 200+ symptoms and experiences, per its App Store listing

Pros

• A strong privacy reputation: Mozilla's July 2026 review scored Clue 8 out of 10, the highest of the three apps here
• A science-first build, with a published study ranking it first among 20 accurate free apps
• Detailed symptom logging that suits cycles that aren't textbook

Cons

• Deeper analysis and advanced predictions sit behind Clue Plus ($9.99/month or $39.99/year as of October 2026), and free users may see prompts to upgrade
• A smaller community than Flo's, with fewer discussion features
• No astrology or lifestyle framing if that's part of what keeps you engaged with a tracker

Pricing

Free: Free to download, with cycle and symptom tracking; Clue Plus adds more.

Clue Plus: $9.99/month or $39.99/year as of October 2026, per its App Store listing. Adds deeper analysis, advanced predictions, and personalized insights. Check current pricing in-app.

Download: Available on iOS and Android

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What do you get with Stardust?

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. Its App Store listing shows a 4.8 out of 5 rating across about 119K ratings (as of October 2026).

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
• Sleep and activity insights layered onto cycle tracking, plus the option to connect wearables like Apple Watch and Oura Ring for basal body temperature
• Sharing with partners or close friends, plus Pregnancy Mode with week-by-week tracking

Pros

• Genuinely fun to open, which is a real reason people stick with a tracker instead of abandoning it after a week
• Free to download, with in-app purchases
• Revised its privacy policy to remove end-to-end encryption mentions after 2022 reporting

Cons

• Its privacy label lists purchases, identifiers and usage data among the data used to track you (App Store listing)
• Mozilla's July 2026 review scored it 2 out of 10, the lowest of the six apps tested
• Its main privacy policy was revised twice in roughly seven months and now names Meta's and Google's ad-measurement tools as partners (see below)

Pricing

Free: Free to download; the paid tier unlocks more.

Paid plans: the US App Store lists a $6.99 Monthly Plan and annual plans at $24.99–$39.99 (as of October 2026, per the listing). Check current pricing in-app.

Download: Available on iOS and Android

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How do Flo, Clue, and Stardust handle your data?

This is the section most comparisons skip. 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 and what their public record shows. Everything below is sourced and current as of October 2026.

Flo: FTC Order, Class Action, and a 2025 Verdict

The FTC finalized an order against Flo in June 2021 after alleging Flo shared sensitive health data from millions of users with firms including Facebook and Google despite promising privacy; the order did not include a fine. A separate class action over the same 2016–2019 data sharing reached a proposed $59.5M settlement with Google, Flo and Flurry (Flo's share: $8M; the defendants deny wrongdoing). It received preliminary approval in April 2026, with a final approval hearing set for October 29, 2026 (court-approved notice). Separately, a jury found Meta liable in August 2025 (Femtech Insider).

Flo has since added Anonymous Mode, which its App Store listing describes as letting you track without personal identifiers linked to your health data. 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 Its Public Statements

Clue is based in Berlin, Germany (BioWink GmbH), so EU GDPR applies to its handling of your data. Clue said in June 2022 that it would not respond to any disclosure request or subpoena of its users' health data by US authorities and had never received such a request (Clue statement). Its privacy policy says tracked health data is never shared with or sold to advertisers, while disclosing that ad networks receive technical data such as app-install and subscription events, and notes that non-EU processors could be subject to access by public authorities. Clue's App Store listing describes the app as a regulated medical device, but its privacy label still lists identifiers used to track you. Mozilla's July 2026 review gave Clue 8 out of 10. We found no FTC action or class action against Clue in our research.

Stardust: 2022 Criticism, Then a 2026 Mozilla Review

In June 2022, TechCrunch reported that Stardust periodically sent users' phone numbers to the analytics firm Mixpanel (TechCrunch saw no health data shared with it), and that Stardust's promised end-to-end encryption was unclear: the founder described standard SSL traffic and AES-256 storage on AWS. Its privacy policy at the time allowed disclosure to law enforcement "whether or not legally required," which drew attention after Roe v. Wade was overturned. After TechCrunch got in touch, Stardust revised the policy to remove its end-to-end encryption mentions.

On July 16, 2026, Mozilla published a hands-on review of six period trackers. As reported by PPC Land, Stardust scored 2 out of 10, against 8 for Clue and 7 for Flo. TechCrunch reported that Stardust was the only one of the six to send sensitive health data (birthdate, contraceptive method, family-planning intentions and symptoms) to another company, the analytics firm RudderStack, tied to an identifier rather than a name. A Stardust spokesperson said RudderStack is "contractually prohibited from selling or using it for its own purposes." Mozilla also found the main privacy policy had been revised twice in roughly seven months, naming Meta's and Google's ad-measurement tools as partners as of May 2026 (per PPC Land). Stardust told TechCrunch it "has never received any requests, demands, or legal process for user data from authorities or third parties." Read the current version of the policy yourself if this is a deciding factor for you.

Taken together, the picture on paper: In Mozilla's July 2026 review of six period trackers, Clue scored 8 out of 10, Flo 7 and Stardust 2 (PPC Land). That is one review of six apps, and Flo's record includes an FTC order and a class action that Flo has settled while denying wrongdoing, alongside real changes since. None of that means any one app is "unsafe," but it's worth knowing before you decide where years of period, mood, and symptom data lives.

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Is there a fourth option besides Flo, Clue, and Stardust?

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. Veya 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, alongside mood, sleep, fitness, and nutrition.

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

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 570M+ downloads, Clue's long 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

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Should you choose Flo, Clue, or Stardust?

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:

If OPK and LH-strip tracking matters more to you than general cycle tracking, our Premom vs Flo comparison is the more direct pick.

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Frequently Asked Questions

How do Flo, Clue, and Stardust compare?

All three track your cycle, but they're built around different priorities. Flo has a very large community and a deep content library (Flo Premium annual plans are listed at $47.99–$59.99). Clue is a Berlin-based, science-first app (Clue Plus is $39.99/year). Stardust wraps cycle tracking in moon-phase and astrology content (annual plans are listed at $24.99–$39.99). Prices are from the US App Store as of October 2026. Standard tracking in all three is not birth control. Which one fits depends on whether you want community and depth, science and privacy, or a tracker that feels like a daily ritual.

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

In Mozilla's July 2026 review, Clue scored 8 out of 10, Flo 7 and Stardust 2 (PPC Land). Clue is based in Berlin and subject to EU GDPR, and said in 2022 it would not respond to US disclosure requests for user health data (Clue statement). The FTC finalized an order against Flo in June 2021 after alleging Flo shared sensitive health data from millions of users with firms including Facebook and Google despite promising privacy; the order did not include a fine. A separate class action over the same 2016–2019 data sharing reached a proposed $59.5M settlement with Google, Flo and Flurry (Flo's share: $8M; the defendants deny wrongdoing). It received preliminary approval in April 2026, with a final approval hearing set for October 29, 2026 (court-approved notice). Separately, a jury found Meta liable in August 2025 (Femtech Insider). Flo has since added Anonymous Mode, which its App Store listing describes as letting you track without personal identifiers linked to your health data. For Stardust, in 2022, TechCrunch reported that Stardust periodically sent users' phone numbers to the analytics firm Mixpanel (TechCrunch saw no health data shared with it), and that Stardust's promised end-to-end encryption was unclear: the founder described standard SSL traffic and AES-256 storage on AWS. Its privacy policy at the time allowed disclosure to law enforcement "whether or not legally required," which drew attention after Roe v. Wade was overturned. After TechCrunch got in touch, Stardust revised the policy to remove its end-to-end encryption mentions. Check each app's current privacy policy yourself.

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

All three are free to download, but they differ in what's included. Flo lists some features, such as its virtual Health Assistant, as Premium. Clue's free version covers cycle and symptom tracking, with Clue Plus adding deeper analysis, advanced predictions, and personalized insights. Stardust is free with in-app purchases. Compare what's free in each app before subscribing.

Is Clue a medical device?

Clue's App Store listing describes the app as a regulated medical device. Its standard period and cycle tracking is not birth control. Clue also received a 2021 FDA clearance for a separate Clue Birth Control feature, but its current listing doesn't list a birth-control mode. A regulated-device status for prediction features is not a promise that predictions are accurate for you.

What happened with Stardust's privacy policy in 2026?

Mozilla published a review of six period trackers on July 16, 2026 and, as PPC Land reported, scored Stardust 2 out of 10. TechCrunch reported that Stardust was the only one of the six to send sensitive health data to another company (RudderStack), tied to an identifier rather than a name. The main privacy policy was also revised twice in roughly seven months, and it names Meta's and Google's ad-measurement tools as partners as of May 2026. This came after the 2022 criticism over phone numbers shared with an analytics firm and unclear encryption claims (TechCrunch, 2022).

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

Veya, our app, 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?

Standard period and cycle tracking in Flo, Clue, and Stardust is not birth control, and none of them should be used as contraception. Natural Cycles is an app the FDA has authorized for contraception (FDA De Novo grant). Clue also received a 2021 FDA clearance for a separate Clue Birth Control feature, but its current App Store listing doesn't list a birth-control mode. If app-based birth control is what you're after, that's a conversation to have with a healthcare provider.

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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

• Clue vs Stardust: Which Period Tracker Fits You? (2026)
• Flo vs Natural Cycles: Which One Should You Use?
• Clue vs Natural Cycles: Which One Should You Use?
• Flo vs Veya: Which One Should You Use?
• Best Cycle Syncing Apps 2026: 28 vs Stardust vs MyFlo vs Flo