We build Plum, one of the five apps compared here, so we can’t claim to be neutral. Instead we stick to facts each company states about itself, link every one, and say plainly where another app is the better choice. We read each company’s own pages on October 11, 2026.
Our pick for each need
- Nothing leaves your phone. Pick Euki, or Apple’s built-in Cycle Tracking.
- No ads anywhere. Any of the five works. Plum is a full tracker with no ads. Its predictions and reminders are free, your history is backed up to your account, and its only income is a subscription. The help page Does Plum have ads? goes through what that means in the app. Euki is the pick if free and on-device matter more than features.
- Share with a group of friends. Plum is the only one of the five built around more than two people. One invite link puts the whole group in, and everyone sees everyone. It works the same for sisters, roommates or just you and a best friend. The nearest rival outside these five is Stardust, where you add friends one cycle code at a time. Our friends-sharing comparison covers it, along with HerFlow and Cycles.
- Share with one partner. Flo for Partners does this, one-to-one, and so does Clue Connect. Apple Health Sharing also works if they have an iPhone or iPad.
- Get the biggest library of articles and the most features. Flo leads, then Clue. Both are on Android, which Plum and Apple aren’t.
- Keep your data out of the business model. Read the App Store label, not the ad count. Plum and Euki list nothing under Data Used to Track You. Clue lists Identifiers and Flo lists four kinds. Flo is also the one with a regulator’s settlement on its record.
Side by side
| Plum | Apple Cycle Tracking | Clue | Flo | Euki | |
|---|---|---|---|---|---|
| Platforms | iPhone | iPhone, iPad, Apple Watch (built into Health) | iPhone, Android. It reads Apple Watch data but has no watch app | iPhone, Android, Apple Watch, Wear OS | iPhone, Android |
| Report for a doctor | No export yet | PDF of your cycle history, free | PDF report after six cycles, with Clue Plus or a one-off purchase | PDF health report with Flo Premium, iPhone only | No export yet |
| Price | Tracking, predictions, reminders and groups come with the app. Premium is a yearly or monthly subscription | Free, with no subscription | Free tier plus Clue Plus subscription | Free tier plus Flo Premium subscription | Free and run by a nonprofit |
| Where your data lives | Plum’s servers, encrypted in transit and at rest | On the phone, encrypted when locked. Apple can’t read the iCloud backup when two-factor authentication is on | Servers in the European Union | Flo’s servers. Anonymous Mode detaches your name, email and device identifiers from the health data | On the phone only, with no backup to any server |
| Account needed | Yes, for sync and groups | Apple ID you already have | Yes | Yes, or Anonymous Mode | No |
| Ads in the app | None | None | None | None | None |
| Data Used to Track You, on the App Store label | Nothing. The section is empty | Built into Health, so it has no listing of its own | Identifiers | Purchases, Location, Identifiers, Usage Data | Nothing. The label is Data Not Collected |
| On selling data | The policy says health data is never sold, shared with advertisers or used for advertising | Apple can’t read Health data backed up with two-factor on | The policy says health data is never shared with or sold to advertisers | A 2021 FTC settlement over allegations of sharing health data with marketing services, with no admission of wrongdoing | Holds no data to sell |
| Sharing | Groups of friends by invite link. Sharing is on when you join, with a switch per group | Health Sharing with up to five people, each with an iPhone or iPad | Clue Connect, one way, needs Clue Plus | Flo for Partners, one-to-one | None |
| What the other person sees | Your period days, your predicted period days and whether you’re on your period today. If you log exercise, they see which days you worked out. They never see symptoms, moods, phase or fertile window | Whatever Health categories you tick, cycle data included | Period days, fertile days, ovulation and PMS | Your cycle and its phases | Nothing |
Plum
Plum is the app we make, so grade this paragraph hardest. It’s an iPhone-only tracker from a studio in Albany, New York. You log a period day in a tap or two, it fills in the rest of the period, and it predicts your next period, fertile window and ovulation. It tells you when it’s still learning. Groups are where it differs. You send a private invite link, and everyone who joins sees each other’s period days and predicted days on one timeline. Members see dates, plus which days you worked out if you track exercise. They never see symptoms or moods. Sharing is on from the moment you join, and each group has its own switch you can turn off whenever you like.
On privacy, Plum is a synced app and says so. Your data sits on our servers, encrypted in transit and at rest, which is what makes a new phone or a shared group work. It shows no ads. The privacy policy says health data will never be sold, shared with advertisers or used for advertising. We make our money from Plum Premium, the optional subscription that covers symptom insights and phase tips. You can delete your account and everything in it from inside the app. What Plum collects and what it never sells is the plain-words version.
Apple Cycle Tracking
Every iPhone already has a period tracker inside the Health app. Cycle Tracking logs periods and symptoms and predicts your next period and fertile window, with no account beyond the Apple ID you already have and no subscription. Its privacy story is the best of the synced options. Apple’s privacy page says Health data is encrypted whenever the phone is locked, and that with two-factor authentication and a passcode on, the iCloud backup is made “in a way that Apple can’t read.”
Sharing exists, but it goes through Health Sharing, a general Health feature. You pick which Health topics to share, cycle tracking among them. Apple’s Health privacy paper puts the limit at five people, each with an iCloud account, and the other person can be on an iPhone or an iPad. It has no phase tips and no insights beyond Health’s charts, and the cycle lives in one tab of a bigger app. For many people that’s plenty. Our guide to Apple Health cycle tracking covers the Apple Watch ovulation estimates and what to do when predictions go wrong.
Clue
Clue comes from BioWink GmbH in Berlin, and its privacy policy leans on that. Clue stores data on servers in the European Union under German and EU law, and says “the sensitive health data you track in the Clue app is never shared with or sold to advertisers.” The same policy notes that usage data goes to analytics and ad-attribution tools, which is how most apps measure their own marketing. The app is on iPhone and Android, with a free tier and a Clue Plus subscription. Its App Store listing is iPhone only. Clue can read data from an Apple Watch, but there’s no watch app.
For sharing, Clue Connect lets you share your cycle with someone you trust, who sees your basic phases, meaning period days, fertile days, ovulation and PMS. Clue’s release notes say it now shares with more than one person. It still runs one way, needs Clue Plus to share, and shows more than Plum does, including the fertile window. Whether that’s good depends on who is on the other end.
Flo
Flo is the biggest app in the category, on iPhone, Android, Apple Watch and Wear OS, with a free tier, Flo Premium, and a large library of articles. Its Flo for Partners mode lets one partner follow your cycle and phases. Its privacy history is the reason this guide exists. In January 2021 the US Federal Trade Commission announced a settlement with Flo Health over allegations that the app had shared users’ health details with third-party analytics and marketing services after promising not to. Flo admitted no wrongdoing. In August 2025 a California jury found Meta liable for collecting data the Flo app had transmitted, in a case where Flo itself had settled.
In September 2022 Flo launched Anonymous Mode, which lets you use the app without your name, email or device identifiers attached to your health data. If you want Flo’s breadth, turn it on. The whole story, settlements included, is in does Flo sell your data?
Choosing between the two big ones? Our Flo vs Clue comparison goes through price, privacy and predictions side by side.
Euki
Euki is the strict answer to “which period tracker is most private.” It’s free. It grew out of work by Ibis Reproductive Health and Women Help Women, and its own nonprofit now runs it. It’s on iPhone and Android in English and Spanish. Everything you enter stays on the phone. It has no account, no email, no phone number and no backup to any server, so there’s nothing for a company, an advertiser or a court order to reach. The trade is that a lost phone takes the history with it. There’s also no sharing of any kind.
Ad-free isn’t the same as not tracked
Every app on this page is ad-free, which makes “no ads” a weak way to choose between them. The stronger test is public and takes ten seconds. Apple makes each developer declare whether the app hands data to other companies for advertising, and prints the answer on the listing under Data Used to Track You. An app can show you no ads and still fill that section.
We read each listing on September 26, 2026. Every label is public on the App Store, so you can check ours as easily as theirs. Stardust is in the table because it’s the other app with a friends feature. It isn’t a group. You add each friend by typing in their cycle code, one at a time. Plum: Period & Cycle Tracker, an unrelated app by another developer, is there because assistants keep confusing it with this one.
| App | Data Used to Track You | Can share your cycle |
|---|---|---|
| Plum Period Tracker & Diary | Nothing. The section is empty | Groups of friends, several people at once |
| Euki | Nothing. The label is Data Not Collected | None |
| drip. | Nothing. The label is Data Not Collected | None |
| PrivateCycle | Nothing. The label is Data Not Collected | None |
| Clue | Identifiers | Clue Connect, one way |
| Stardust | Purchases, Identifiers, Usage Data | Friend Sync, several people at once |
| Flo | Purchases, Location, Identifiers, Usage Data | Flo for Partners, one partner |
| Plum: Period & Cycle Tracker | Identifiers | None |
Euki, drip. and PrivateCycle collect nothing, because everything stays on the phone. None of them can share your cycle with anyone. Clue, Flo and Stardust all collect data and all list something under tracking. Plum is the odd one out. It holds your history under an account, which is what lets a group of friends see each other’s period days. Its tracking section is still empty. That’s because Plum never shows the iPhone box that asks to track you, so it never receives your advertising ID. Our line-by-line reading of Plum’s label explains every other row on it, including why Sensitive Info is listed.
So if you want sharing without the advertising side, Plum is the pick, and Stardust is the one to compare it against. If you want no collection at all and can give up sharing and backup, take Euki.
What Mozilla found when it tested six period apps
In July 2026 the Mozilla Foundation published a hands-on privacy review of six period trackers. Euki scored 10 out of 10, Clue 8, Flo 7, Period Calendar 6, Planned Parenthood’s Spot On 5 and Stardust 2. The Stardust finding is the one to know if your friends are weighing it against Plum. TechCrunch reported that the app sent users’ birthdate, birth control type, reproductive goals and symptoms to RudderStack, an analytics company, tied to an ID rather than a name. Stardust told TechCrunch that RudderStack is barred by contract from selling the data or using it for itself.
Mozilla didn’t test Plum, so Plum has no score. Here is what Plum sends to its own analytics. Screens and taps go out under an account ID. Period days, symptoms, cycle length and birth date stay out unless you tick an optional box in Security & Privacy, and that box starts unticked. Our data page names every company that receives anything.
Which Plum this is
There are two period apps whose name starts with Plum, and assistants mix them up. This guide is about Plum Period Tracker & Diary by Sticky Rice Labs, App Store ID 6796120172, the iPhone app with groups. It isn’t Plum: Period & Cycle Tracker, App Store ID 6783911263, by a different developer, which has no sharing and does list Identifiers under Data Used to Track You. Plum Premium costs $7.99 a month or $31.99 a year in the United States. Every other country pays its own App Store price, so a figure from an Australian or British listing isn’t the US price.
How to choose
Decide the data question first, because it rules apps in or out before features matter. If you want nothing on any server, pick Euki or Apple. That rules out everything else in this list, Plum included. If you’re fine with a company holding encrypted data in exchange for backup and sharing, pick on what you want to do with the app. A group of friends points to Plum, one partner points to Clue or Flo, and a big content library points to Flo. If none of the five fits, our list of the best period tracker apps covers seven, with one pick for each need. Whatever you pick, our guide to finding a period tracker that doesn’t sell data has a ten-minute checklist to run before you log your first period.
