Most “best period tracker” lists come from people who have never opened the privacy policies. We build one of these apps, so we know the category too well to pretend to be neutral. What we can do is 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 August 30, 2026.
The short version
- Nothing leaves your phone. Pick Euki, or Apple’s built-in Cycle Tracking.
- Share with a group of friends. That’s Plum, the only one of the five built around more than two people. Our friends-sharing comparison adds Stardust, HerFlow and Cycles.
- Share with one partner. Clue Connect and Flo for Partners both do this, one-to-one. Apple Health Sharing also works if they have an iPhone.
- 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. Plum, Clue, Euki and Apple all do, with no ads. Flo is ad-free too, but its record on data sharing is the one with a regulator’s settlement in it.
Side by side
| Plum | Apple Cycle Tracking | Clue | Flo | Euki | |
|---|---|---|---|---|---|
| Platforms | iPhone | iPhone, Apple Watch (built into Health) | iPhone, Android, Apple Watch | iPhone, Android | iPhone, Android |
| Price | Tracking, predictions, reminders and groups come with the app. Premium is a subscription with a free trial | Free, no subscription | Free tier plus Clue Plus subscription | Free tier plus Flo Premium subscription | Free, run by a nonprofit |
| Where your data lives | Plum’s servers, encrypted in transit and at rest | On the phone, encrypted when locked. iCloud backup Apple cannot read with two-factor authentication 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, 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 |
| On selling data | Policy: health data never sold or shared with advertisers, never used for advertising | Apple cannot read Health data backed up with two-factor on | Policy: health data never shared with or sold to advertisers | 2021 FTC settlement over allegations of sharing health data with marketing services, no admission of wrongdoing | Holds no data to sell |
| Sharing | Groups of friends by invite link. Sharing off per group until you turn it on | Health Sharing with up to five people, each needs an iPhone | Clue Connect, one-to-one | Flo for Partners, one-to-one | None |
| What the other person sees | Last period, next expected period, on period today. Never notes, symptoms, 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, telling you when it’s still learning rather than pretending to be sure. 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 only, never notes or symptoms, and sharing stays off for each group until you switch it on.
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, and the company makes its 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.
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 is Health Sharing rather than a period feature. Apple’s support article says you can share categories of Health data, cycle tracking among them, with up to five people, each of whom needs an iPhone and an iCloud account. It has no phase tips, no insights beyond Health’s charts, and the cycle lives in a tab rather than being the whole app. For many people that is plenty.
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, Android and Apple Watch, with a free tier and a Clue Plus subscription.
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. It is one-to-one and shares more than Plum does, including the fertile window, which is either a feature or a problem depending on who is on the other end.
Flo
Flo is the biggest app in the category, on iPhone and Android, 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.
Flo has changed since. In September 2022 it 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 that on.
Euki
Euki is the strict answer to “which period tracker is most private.” It is free, started by the nonprofit Women Help Women and now run by its own nonprofit, on iPhone and Android in English and Spanish. Everything you enter stays on the phone. There is no account, no email, no phone number, and no backup to any server, which means there’s also nothing for a company, an advertiser or a court order to reach. The trade is that a lost phone takes the history with it, and there is no sharing of any kind.
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, it is Euki or Apple, and everything else in this list is disqualified, Plum included. If you are 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. Whatever you pick, run our ten-minute privacy checklist before you log your first period.
Common questions
What is the most private period tracker?
The most private are the ones that never send your data anywhere. Euki stores everything on the phone, needs no account and is free. Apple's built-in Cycle Tracking keeps Health data encrypted on the device, with iCloud backups Apple cannot read once two-factor authentication is on. Every synced tracker, Plum included, holds your history on a server, so for those the test is the privacy policy. It should rule out selling and advertising use, describe encryption, and stand behind a delete button that deletes.
Which period tracker lets you share your cycle with friends?
Plum is built around groups. You send a private invite link, and everyone who joins sees each other's last period, next expected period and whether they are on their period today, on one shared timeline. Clue Connect and Flo for Partners are one-to-one, aimed at a partner, and Apple's Health Sharing can include cycle data for up to five people who each have an iPhone. Euki has no sharing at all, on purpose.
Is Apple's Cycle Tracking good enough, or do I need an app?
For logging periods and seeing the next predicted period and fertile window, it's good enough, and no synced option is more private, since iCloud Health data is end-to-end encrypted with two-factor authentication on. You need a separate app if you want phase tips, symptom insights, a group of friends on one screen, or an interface built around the cycle rather than a tab inside Health.
Plum vs Flo: what is the difference?
The difference is size and focus. Flo is the largest period app, on iPhone and Android, with a big library of articles and a one-to-one partner mode. Plum is a small iPhone app built around sharing with a group of friends, with no ads and a subscription as its only revenue. Flo settled with the US Federal Trade Commission in 2021 over allegations it shared health data with marketing services, and has since added an Anonymous Mode. Plum's privacy policy says health data is never sold or shared with advertisers.
Plum vs Clue: what is the difference?
Both are ad-free and funded by a subscription, and both say plainly that health data is not sold to advertisers. Clue is a Berlin company with data on EU servers, apps for iPhone, Android and Apple Watch, and Clue Connect for sharing with one person. Plum is iPhone only, shares through groups with several friends at once, and includes more without a subscription. Predictions, reminders and groups come with the app, and Premium covers insights and tips.
Does Plum sell period data?
No, it doesn't. Plum shows no ads and its privacy policy says it will never sell health data or share it with advertisers. It makes money from Plum Premium, a subscription. Plum syncs your data to its servers, encrypted in transit and at rest, and you can delete your account and everything in it from inside the app.
