We make Plum, one of the apps on this list. That’s the first thing to know about any “best period tracker” article, because most of them are written by a company that sells one, and they rarely say so up top. Here is how this one works. Every claim about another app comes from that company’s own site, help centre or App Store listing, linked, and we read each of them on September 3, 2026. Where another app is the better choice, this page says so. Where Plum is, it says that too, and you can grade that paragraph hardest.
The short version
- Sharing with a group of friends. Plum. It’s the only app here built around more than two people.
- Nothing on any server. Euki, or Drip if you want it open source and on Android.
- Already on your iPhone. Apple’s Cycle Tracking, inside the Health app.
- Irregular cycles, perimenopause and clinical detail. Clue.
- The most features and the biggest library. Flo, with Anonymous Mode turned on.
- Birth control. Natural Cycles, the only app here cleared for that. None of the others is, Plum included.
How we chose
We didn’t score anything, and there are no affiliate links. We read each company’s own pages and asked the same six questions of every app. What platforms is it on? What does it cost, and what is behind the subscription? Where does your data live, and does the privacy policy rule out selling it or using it for ads? Do you need an account? Can you share your cycle, with whom, and what do they see? And what is the one thing it does better than the rest? An app made the list if it is the clear pick for at least one of those answers. Popularity alone wasn’t enough, which is why a few big names are absent.
We set one rule from the start. No dollar amounts, because App Store prices change by country and by month, and a stale price is worse than none. Where a subscription exists, the table says what it unlocks and the store shows the price.
Plum, for sharing with a group of friends
Plum is an iPhone app from a small 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. When it hasn’t seen enough cycles yet it says it is still learning rather than pretending to be sure. Predictions, reminders and groups come with the app. Plum Premium, the subscription, adds symptom insights and phase tips.
Groups are the reason it’s on this list. 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. Members see dates only. Notes, symptoms, phase and fertile window are never shared, and sharing stays off for each group until you turn it on. Every other app here shares one-to-one, or not at all. Our friends-sharing comparison covers Stardust, HerFlow and Cycles as well.
There are caveats. Plum is a synced app. Your data sits on its servers, encrypted in transit and at rest, and you need an account. The privacy policy says health data will never be sold, shared with advertisers or used for advertising, there are no ads, and you can delete your account and everything in it from inside the app. There is no Android version. And its predictions are not a form of contraception, which is true of every app here except one.
Euki, for keeping everything on the phone
Euki is the strict answer to “which period tracker is most private”. Its own site carries the WIRED line that the five most popular period apps all falter next to more secure options like Euki. It’s free, open source, and run by an independent nonprofit. There is no account, no email and no backup to any server, so there’s nothing for a company, an advertiser or a court order to reach. It’s on iPhone and Android in English and Spanish, and it tracks pregnancy too. The trade is that a lost phone takes the history with it, and there is no sharing of any kind, by design.
Drip, for open source on Android
Drip is the other on-device option, an open-source project whose code is public on GitLab. Its own site puts it plainly. Everything you enter stays on your device. It tracks periods, and if you want it to, fertility by the symptothermal method, with temperature and cervical mucus. It’s on iPhone and Android, and you can install the Android build directly as an APK without the Play Store. It’s deliberately not cute, in its own words, and it’s the pick if you want to read the code that predicts your cycle. No account, no sharing, no subscription.
Apple Cycle Tracking, for the app you already have
Every iPhone ships with a period tracker inside the Health app. Cycle Tracking logs periods and symptoms, predicts your next period and fertile window, and needs no account beyond the Apple ID you already use. Apple’s privacy page says Health data is encrypted whenever the phone is locked, and that with two-factor authentication on, the iCloud backup is made in a way Apple can’t read. For dates and a prediction, that is hard to beat.
Sharing is Health Sharing, not a period feature. Apple’s support article says you can share categories of Health data, cycle tracking among them, with up to five people who each need an iPhone. They see your data inside their own Health app, one-to-one, so it’s private and not very social. There are no phase tips and no insights beyond Health’s charts.
Clue, for irregular cycles and clinical detail
Clue comes from Biowink GmbH in Berlin, and its product pages go further into the hard cases than anyone else’s, with dedicated modes for trying to conceive, pregnancy, perimenopause and cycles with no period at all. It runs on iPhone, Android and Apple Watch, with a free tier and a Clue Plus subscription, and it publishes its own research. Its privacy policy keeps data on servers in the European Union and says the health data you track is never shared with or sold to advertisers.
For sharing, Clue Connect lets you share with one person at a time, who sees your period days, fertile days, ovulation and PMS on their own calendar. Sharing needs Clue Plus; viewing is free. It’s a partner feature and works well as one.
Flo, for the most features
Flo is the largest app in the category. Its own site claims over 420 million people have used it to track periods, ovulation, pregnancy and perimenopause, and the app carries a health library, a symptom checker, calculators and Flo for Partners, a one-to-one partner mode. It’s on iPhone and Android with a free tier and Flo Premium. If you want the most things in one app, this is it.
Its privacy record is the reason people ask for alternatives. In 2021 the US Federal Trade Commission announced a settlement with Flo Health over allegations that the app shared users’ health details with analytics and marketing services after promising not to. Flo admitted no wrongdoing, and in 2022 it launched Anonymous Mode, which detaches your name, email and device identifiers from your health data. Use Flo with that on.
Natural Cycles, for birth control
Natural Cycles is the only app here cleared by the US Food and Drug Administration as a form of birth control, which is the reason it’s on this list. It says so on its home page, along with its own effectiveness figures. It works from your body temperature, taken with a measuring device the app pairs with, and it costs a subscription plus that device. If the question you’re asking is “can I use a period app instead of contraception”, the answer is no for every other app on this page, Plum included, and this is the one built and regulated for that job.
Side by side
| Platforms | Cost | Where your data lives | Account | Sharing | |
|---|---|---|---|---|---|
| Plum | iPhone | Tracking, predictions, reminders and groups included. Premium subscription for insights and tips | Plum’s servers, encrypted in transit and at rest | Yes | Groups of friends by invite link, dates only |
| Euki | iPhone, Android | Free, nonprofit | On the phone only | No | None |
| Drip | iPhone, Android | Free, open source | On the phone only | No | None |
| Apple Cycle Tracking | iPhone, Apple Watch | Free, built in | On the phone, iCloud backup Apple can’t read with two-factor on | Apple ID | Health Sharing with up to five people, one-to-one |
| Clue | iPhone, Android, Apple Watch | Free tier plus Clue Plus | Servers in the European Union | Yes | Clue Connect, one person, needs Clue Plus |
| Flo | iPhone, Android | Free tier plus Flo Premium | Flo’s servers, Anonymous Mode available | Yes, or Anonymous Mode | Flo for Partners, one partner |
| Natural Cycles | iPhone, Android | Subscription | Natural Cycles’ servers | Yes | Not a sharing app |
What to look for in any period tracker
- A privacy policy that names advertisers. The good ones say health data is never sold or shared with them. A policy that only says “we take privacy seriously” hasn’t said anything. Our ten-minute checklist walks through one.
- A prediction that admits doubt. Cycles vary, and an app that pins a date with no range will be wrong and confident about it. Look for a range, or a plain “still learning”. This matters most with PCOS and other irregular cycles.
- Sharing you control. Know who can see what before you connect anyone, and whether the fertile window travels with the period dates. In some apps it does.
- A diary you’ll keep. Symptoms and notes logged the same day are what a clinician can read later. Our period diary guide covers what to put in it.
- A delete button that deletes. Deleting the app is not deleting the account. The app should do the second one from inside its settings.
- No contraception claims, unless it is cleared for that. A fertile window is an estimate. Only Natural Cycles on this list is regulated as birth control.
Common questions
What is the best period tracker app for iPhone?
It depends on what you want from it. Apple's Cycle Tracking is already in the Health app, costs nothing and keeps your data on the phone, so start there if you only want dates and a prediction. Clue and Flo add symptom insights, articles and Android apps. Euki is the pick if you want no account and nothing on a server. Plum is the pick if you want a group of friends to see each other's period dates on one timeline.
Which period tracker doesn't need an account?
Euki, Drip and Apple's Cycle Tracking all work without one. Euki and Drip keep everything on the phone and never sync, which also means a lost phone takes the history with it. Apple uses the Apple ID you already have and backs Health data up to iCloud in a form Apple can't read once two-factor authentication is on. Plum, Clue and Flo all need an account, because syncing and sharing need a server.
What is a good alternative to Flo?
Clue is the closest match. It has the same breadth of tracking, apps for iPhone and Android, EU servers and a privacy policy that rules out sharing health data with advertisers. If your reason for leaving Flo is privacy, Euki goes further and keeps everything on the phone. If your reason is that you want to share with several friends rather than one partner, that's Plum.
Which period tracker is best for irregular periods?
Pick one that shows you a range rather than a single confident date, and that lets you log symptoms alongside dates so a doctor can read them. Clue's product pages cover irregular cycles and perimenopause directly. Plum tells you when it's still learning your cycle instead of guessing. Whatever you use, a cycle that swings by more than about eight days, or goes past 35 days often, is worth a conversation with a clinician.
Is Plum a good period tracker?
We make it, so weigh this answer accordingly. Plum is a small iPhone app with no ads that logs a period in a tap or two, predicts your period, fertile window and ovulation, and lets a group of friends see each other's period dates by private invite link. It syncs to a server, so it isn't the pick if you want on-device only. Predictions, reminders and groups come with the app, and Premium adds insights and phase tips.
Which app is best for keeping a period diary?
Any of Plum, Clue or Flo works, because each lets you log symptoms, mood and notes against a date and read them back by cycle. Plum's diary keeps notes private even inside a group. For what belongs in a diary and what to leave out, our period diary guide covers it.
Which period tracker is best for PCOS?
The best one for PCOS is the one that stays honest when it can't predict. PCOS cycles are long and uneven, and every app's forecast drifts, so what matters is symptom logging you'll keep up and a prediction that says when it's unsure. Clue and Flo both have PCOS material in their libraries. Plum marks a prediction as still learning rather than pinning a date. Our PCOS tracking guide goes into what to log.
