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Clue vs Stardust: Which Period Tracker Fits You? (2026)

Clue and Stardust sit at close to opposite ends of what a period tracker can be. Clue is the Berlin-based, science-forward option, CE-marked as a medical device in the EU, with a clinical design and a research pedigree. Stardust is the New York-based, design-led option, wrapping cycle tracking in moon phases and astrology content that's made it a fixture on TikTok. This guide covers what each tracks, how their predictions work, how their privacy architecture actually differs, pricing, design, and who each one suits.

By Go Go Gaia Team • Published September 7, 2026 • 9 min read • App Comparison

Full Transparency

This comparison is published by Holland Neurotech Inc., the company behind Go Go Gaia. We've included Go Go Gaia as a third option where relevant. We've done our best to compare Clue and Stardust fairly based on each app's published features, pricing, and public record. If Clue or Stardust is the better fit for you, use it.

Quick Answer

Clue and Stardust hold close to opposite ideas of what opening a period tracker should feel like. Clue leans on documentation: a CE mark, published research partnerships, and a decade-plus clean privacy record. Stardust leans on personality, with moon-phase content and a visual style you either love or don't. Go Go Gaia sits outside that split, folding cycle tracking into a broader health record. Here's how the three compare:

  • If science and privacy matter most: Go with Clue. Berlin-based, CE-marked as a Class 1 medical device, with research partnerships and a clean public record.
  • If the tracker itself needs personality to hold your attention: Go with Stardust. Moon-phase and hormone-stage content, cycle sharing with friends.
  • If you want cycle, symptom, mood, and lab tracking in one free app: Try Go Go Gaia.
Person journaling in the morning, comparing Clue and Stardust period trackers

Clue and Stardust rarely get compared directly, and that's part of why the comparison is useful. They're not chasing the same user. Clue was built in Berlin in 2012 around a clinical, research-backed approach to cycle prediction, and it's since become a CE-marked medical device in the EU. Stardust was built in New York around a design-forward, moon-phase, astrology-flavored take on the same core job, tracking your cycle, and it's built a large following on TikTok off the back of that look.

Both companies also handle your data very differently, and that difference showed up clearly in a Mozilla Foundation privacy review published in July 2026. We'll walk through what you get with each app, how their approaches to privacy actually compare, and a third option built around a different premise: tracking your whole health picture rather than just your cycle.

The Short Version

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

Clue Stardust Go Go Gaia
Best for Science and privacy Daily ritual, astrology feel Whole-health tracking
Company base Berlin, Germany New York, US US-based
Platform iOS + Android iOS + Android iOS only (+ web app)
Design Clinical, minimal Moon-phase, astrology visuals Simple, metric-focused
Premium price (annual) ~$39.99/yr ~$24.99–$39.99/yr ~$49.99/yr
Privacy record CE-marked, GDPR, clean record 2/10 in a Jul 2026 Mozilla review No ads, no data selling

Want more detail? Keep reading.

Clue: What You Get

Clue was founded in Berlin in 2012 by Ida Tin, Hans Raffauf, Moritz von Buttlar, and Mike LaVigne, and it's built its identity around a clinical, research-driven approach to cycle tracking.[1] The app is CE-marked as a Class 1 medical device in the EU as of 2023, and its US App Store listing carries an FDA Owner/Operator number for its regulated operations there.[1][3] Clue's own materials describe its algorithm and product decisions as grounded in research partnerships with institutions including Oxford and the Kinsey Institute.[1]

Features

  • Cycle tracking with predictions Clue describes as clinically validated
  • 200+ symptom and experience categories, including cramps, mood, energy, skin, and sleep
  • Ovulation and fertile-window predictions
  • 400+ science-backed articles
  • Wearable sync, including Apple Watch, Oura, WHOOP, Withings, and Fitbit (some syncing may require Clue Plus, check the app for your tier)
  • Clean, gender-neutral, clinical interface

Strengths

Privacy is Clue's clearest advantage. It's based in Berlin, subject to strict EU GDPR rules, and states on its own site that it has never sold health data or shared it with any authority.[2] There's no public enforcement action or class action on record for Clue.

The science-first framing is real, not just marketing copy. Clue points to specific research partnerships and describes its prediction approach as clinically validated, and the app is CE-marked as a medical device in the EU.[1] If you want a tracker built with that kind of documentation behind it, Clue is one of the few that offers it.

The design stays out of the way. No zodiac signs, no lunar framing. Just cycle and symptom data in a minimal interface, which a lot of people specifically want after trying trackers with more personality baked in.

Limitations

The free tier has gotten thinner over time. Basic cycle and symptom tracking is free, but pregnancy mode, deeper insights, and full wearable sync sit behind Clue Plus (~$39.99/year, or ~$9.99/month, as of September 2026).[3] Some users find the upgrade prompts frequent.

No nutrition, fitness, or mood-focused tracking beyond symptoms. Clue stays centered on cycle and reproductive health. If you want meal logging, workout tracking, or a dedicated mood log alongside your cycle, that's a separate app.

No astrology or lifestyle framing, which is either a strength or a limitation depending on what keeps you opening a tracker consistently.

Pricing

Free: Cycle and symptom tracking, ovulation predictions, article library.

Clue Plus: ~$9.99/month or ~$39.99/year as of September 2026. Adds pregnancy mode, deeper cycle insights, and fuller wearable integration. Check current pricing in-app, as it varies by region.[3]

Download: Available on iOS and Android

📆 Period Calculator

Predict your next 6 periods instantly.

Try It Free

Stardust: What You Get

Stardust is developed by Stardust App LLC, based in New York, and describes itself as founded and led by women.[4] It pairs standard period tracking with moon-phase visuals, zodiac-flavored "witch type" content, and a distinct look that's made it one of the more design-forward period apps around, with a 4.8 out of 5 rating from roughly 116,000 App Store ratings as of September 2026.[4]

Features

  • Cycle, ovulation, and hormone-stage tracking with a daily readout of what a given phase can feel like
  • A moon-phase wheel that lines up lunar phases with your cycle, plus zodiac and "witch type" content
  • Pregnancy tracking, including a 3D and AR baby visualization feature[4]
  • Symptom logging covering flow, cervical mucus, feelings, cravings, and cycle disruptors
  • Wearable data from Apple Watch and Oura Ring[4]
  • Friend and partner sharing for comparing cycles

Strengths

It's genuinely fun to open. Stardust is one of the few trackers people describe that way. The daily hormone narrative and moon-phase framing make cycle tracking feel less like a chore, and that's a real reason people keep using a tracker instead of abandoning it after a week.

The core experience is free. Cycle tracking, symptom logging, and the daily content are available without paying, with Stardust Plus as an optional add-on.

The feature set has grown. Pregnancy tracking and wearable sync with Apple Watch and Oura Ring are both listed as current features, which is more than some lighter astrology-flavored trackers offer.[4]

Limitations

Its privacy record is the biggest thing to weigh. A Mozilla Foundation review published in July 2026 gave Stardust a score of 2 out of 10, the lowest of six period apps it tested, after finding the app sent data to third-party tracking services before users entered any information, and separately shared sensitive details like birth control type and specific symptoms with a data management firm.[5][6] That sits alongside Stardust's own public claim that it never sells or shares personal health information, so it's worth reading the current policy yourself.[4]

Its privacy policy has kept changing. The same Mozilla review found the policy had been revised twice in about seven months, with the version live as of May 2026 naming Meta's and Google's ad-measurement tools as data partners.[5]

Requires an account, with no local-only mode for people who want cycle data to stay entirely on-device. If any of this rules Stardust out, our Stardust alternatives roundup covers six other trackers.

Pricing

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

Stardust Plus: roughly $6.99/month, or $24.99 to $39.99 a year depending on the offer, as of September 2026. Shorter All Access plans run $2.99 to $4.99. Adds deeper insights and unlimited friend syncs. Check current pricing in-app.[7]

Download: Available on iOS and Android

The Third Option: Go Go Gaia

Clue and Stardust both approach the same job, tracking your period, from different angles: clinical science on one side, daily ritual and design on the other. Neither one tracks mood, sleep, nutrition, or lab results alongside your cycle in real depth. That's the gap Go Go Gaia is built to fill: instead of being a cycle tracker with a few extras, it tracks your whole health picture, cycle included, in one place.

Where It Adds Scope

  • Cycle tracking with automatic phase detection and fertility predictions
  • Whole-health logging: 350+ metrics across mood, sleep, fitness, and nutrition tracked alongside your cycle
  • Support for uploading lab results so they sit next to your cycle and symptom history
  • 1-click logging for fast daily tracking
  • Correlation insights showing how your lifestyle connects to your cycle
  • No ads, no data selling

Honest Limitations

  • No CE mark or clinical research partnerships like Clue's, and no moon-phase or astrology content like Stardust's.
  • iOS only. There's no Android app. A web app covers other platforms, but the full experience is iPhone-only right now.
  • Smaller, newer app. It doesn't have Clue's decade-plus track record or Stardust's TikTok-driven following.
  • 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

🥚 Ovulation Calculator

Find your fertile window and ovulation day.

Try It Free

Side-by-Side Feature Comparison

Here's every major feature compared across all three apps. Check marks mean the feature is included, locks mean it requires a paid subscription, warning signs mean it's limited, and X marks mean it's not available.

Feature Clue Stardust Go Go Gaia
Cycle tracking ✅ ✅ ✅
Pregnancy mode 🔒 Paid ✅ ✅
Symptom tracking ✅ 200+ categories ⚠️ Lighter ✅ Detailed
Mood / whole-health logging ❌ ⚠️ Basic ✅ Mood, sleep, fitness, nutrition
Lab result uploads ❌ ❌ ✅
Moon-phase / astrology content ❌ ✅ Core feature ❌
Wearable integration ⚠️ Apple Watch, Oura, WHOOP, more ⚠️ Apple Watch, Oura ✅ Apple Watch, Oura, Garmin
Medical device / regulatory status ✅ CE-marked (EU), Class 1 ❌ ❌
Content library ✅ 400+ articles ⚠️ Daily readouts, lighter depth ⚠️ Limited
Privacy practices ✅ GDPR, clean record ⚠️ 2/10 Mozilla review, Jul 2026 ✅ No ads, no data selling
Free tier quality ⚠️ Basic, with upsell prompts ✅ Usable core tracking ✅ Generous, no ads
Price (annual) ~$39.99/yr ~$24.99–$39.99/yr ~$49.99/yr

Which Should You Choose?

Neither app is the right answer for everyone. What decides it is which one you'll still be opening in three months, and how heavily Stardust's privacy record weighs on you. Here's the honest breakdown:

Choose Clue if:

  • Privacy and a documented, research-backed approach matter most to you
  • You want a CE-marked app with a clean regulatory and public record
  • You prefer a clinical, no-frills design without lifestyle framing
  • You're comfortable with a focused cycle tracker (no mood, nutrition, or lab tracking built in)

Choose Stardust if:

  • You stopped opening other trackers because they felt like a chore
  • You like moon-phase and daily hormone content more than a plain symptom log
  • You want to sync cycles with friends inside the app
  • You've read the current privacy policy and are comfortable with what it discloses

Choose Go Go Gaia if:

  • You want cycle tracking folded into whole-health logging, symptoms, mood, and lab results
  • You want to see how your lifestyle habits connect to your cycle
  • You want a generous free tier with no ads
  • Astrology framing and clinical certifications aren't why you open a tracker

If your cycles are unpredictable and neither app's calendar-based forecast is working for you, our guide to period trackers for irregular cycles looks at what actually helps there. And if you want Flo added to the mix, Flo vs Clue vs Stardust covers all three together.

Privacy: Two Different Architectures

Cycle and symptom data is sensitive, and Clue and Stardust represent genuinely different approaches to handling it, not just different marketing language. Here's the factual record for each, with dates.

Clue: Berlin, GDPR, and a CE Mark

Clue is based in Berlin, Germany, which puts it under EU GDPR law. Its own site states plainly: "We have never, and will never, sell your health data or share it with any authority."[2] The app became a CE-marked Class 1 medical device in the EU in 2023, a regulatory status tied to how its cycle and ovulation-prediction features are built and documented, not a claim that it functions as birth control. Clue's own listing states it isn't intended for contraceptive use.[1][3] There are no public enforcement actions or class actions against Clue on record.

Stardust: A Low Score From an Independent Review

Stardust's own marketing states it never sells or shares personal health information.[4] A Mozilla Foundation review published in July 2026, part of its Nothing Personal series testing period trackers, found a different picture: Stardust sent data to third-party tracking services from the moment the app opened, before a user entered anything, and separately shared health details including birthdate, birth control type, reproductive goals, and specific symptoms with a data management company.[5] A TechCrunch report on the same research specifically named the third-party recipient as RudderStack, noting a Stardust spokesperson said the company is contractually barred from selling the data or using it for its own purposes.[6] Mozilla scored Stardust 2 out of 10, the lowest of the six period apps it tested.[5]

The same review found Stardust's privacy policy had been revised twice in roughly seven months, with the version live as of May 2026 naming Meta's and Google's ad-measurement tools as data partners receiving activity data.[5] None of this means Stardust is unique in sharing data with third parties, plenty of apps do, but it's the kind of detail worth knowing before deciding where months or years of cycle and symptom data lives. Read Stardust's current privacy policy directly if this is a deciding factor for you.

Go Go Gaia: Privacy-Focused, Smaller Scale

Go Go Gaia doesn't run ads and doesn't sell user data. That said, it's a newer, smaller company without the years of independent privacy review that Clue or Stardust have been through, and it doesn't carry Clue's CE mark. The no-ads, no-data-selling approach is a meaningful commitment, but it hasn't faced the same level of outside scrutiny yet.

Frequently Asked Questions

Is Clue or Stardust more accurate for period predictions?

Both apps use algorithm-based prediction that improves with more logged history, and neither publishes independent accuracy figures against outside data. Clue describes its predictions as built on published cycle research and clinically validated modeling. Stardust layers moon-phase and hormone-stage content on top of its own cycle predictions, but the core method is the same calendar and symptom-based approach most trackers use. For irregular cycles, expect either app's forecast to be less reliable, and lean on the patterns you log rather than the prediction itself.

Which is better for privacy, Clue or Stardust?

Clue has the stronger public privacy record. It's based in Berlin under EU GDPR law, states on its own site that it has never sold health data or shared it with any authority, and has no public enforcement actions on file. Stardust, based in New York, states it never sells or shares personal health information, but a Mozilla Foundation review published in July 2026 found Stardust was the only period app of six tested that sent sensitive health data (including birth control type and specific symptoms) to a third-party analytics company, and that its privacy policy had been revised twice in about seven months, disclosing more ad-partner data sharing including Meta's and Google's ad-measurement tools as of May 2026. Read each company's current privacy policy yourself before logging sensitive symptoms.

Is Clue a medical device?

Clue became a CE-marked Class 1 medical device in the EU in 2023, and its app also lists an FDA Owner/Operator Number for its US operations. That regulatory status covers how its cycle-tracking and prediction features are built and documented, not a claim that the general tracking app functions as contraception. Clue's own listing states it isn't intended to be used for contraceptive purposes.

What happened with Stardust's privacy policy in 2026?

A Mozilla Foundation review published in July 2026, part of its Nothing Personal series on period trackers, gave Stardust a score of 2 out of 10, the lowest of the six apps it tested. The review found Stardust sent data to third-party tracking services before users had entered any information, and separately shared health details like birthdate, birth control type, reproductive goals, and specific symptoms with a data management company. It also found the app's privacy policy had been revised twice in roughly seven months, with the most recent version (as of May 2026) naming Meta's and Google's ad-measurement tools as data partners. Stardust's public marketing states it never sells or shares personal health information, so read its current policy directly if this affects your decision.

What's a good alternative to Clue and Stardust?

If the reason you're comparing is that neither app tracks anything outside your cycle, Go Go Gaia covers different ground: mood, sleep, fitness, nutrition, and uploaded lab results sit in the same record as your cycle, with correlation insights across them. Core features are free with no ads. It's iOS only (a web app covers other platforms), it carries neither Clue's research partnerships nor Stardust's daily content, and it's newer and smaller than both.

References

  1. Clue (Biowink GmbH). About Clue. helloclue.com/about-clue. Fetched September 7, 2026.
  2. Clue (Biowink GmbH). Home. helloclue.com. Fetched September 7, 2026.
  3. Clue. App Store listing. apps.apple.com/us/app/clue-period-tracker-calendar. Fetched September 7, 2026.
  4. Stardust (Stardust App LLC). App Store listing. apps.apple.com/us/app/stardust-period-tracker. Fetched September 7, 2026.
  5. Mozilla Foundation, Nothing Personal. Hands-on privacy testing of six period tracking apps by Shoshana Wodinsky, published July 16, 2026, scoring Stardust 2 out of 10. mozillafoundation.org/en/nothing-personal. Findings summarized in PPC Land, "Mozilla rates Stardust 2 of 10 over symptom data sent to third parties," ppc.land. Fetched September 7, 2026.
  6. TechCrunch. "Period tracker Stardust shares users' health data with analytics firm, says Mozilla research." techcrunch.com. Published July 16, 2026.
  7. Stardust (Stardust App LLC). In-app purchase tiers listed on the App Store. apps.apple.com/us/app/stardust-period-tracker. Fetched September 7, 2026.

Facts checked against official pages and independent reporting, September 2026. Prices and policies change, so confirm current details on each company's site before subscribing or logging sensitive data.

Want to See More Apps Compared?

This guide focused on Clue vs Stardust, but there's more to look at depending on why you're comparing. If Flo is also in the mix, or you want the science-vs-privacy angle taken further, these go deeper.

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Cycle, symptom, mood, sleep, fitness, and nutrition tracking in one app. No ads. 1-click logging.

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