Best Period Tracker Apps
The best period tracker apps trade privacy for features: cloud apps like Flo predict and sync, while an offline planner keeps your whole cycle on your device.
For private, offline cycle tracking, PeriodOS is the strongest pick in this guide. It is a single HTML file that keeps every entry in your own browser, with no account, no server and no cloud, so nothing you log ever leaves your device. If you want algorithmic predictions, a symptom-pattern engine and a community to compare notes with, Flo is the most complete cloud app and Clue is the best-designed one, held under EU privacy law. And if your real goal is birth control rather than tracking, Natural Cycles is the only FDA-cleared option here and the only one built for that job.
| Tool | Best for | Price | Subscription | Works offline |
|---|---|---|---|---|
| PeriodOS | Private, offline cycle tracking | $23 one-time | No | Yes |
| Flo | Predictions, content, community | Free plus premium | Optional | No |
| Clue | Clean design under EU privacy law | Free plus Clue Plus | Optional | No |
| Stardust | Astrology-themed tracking | Free | No | No |
| Natural Cycles | FDA-cleared contraception | Subscription only | Yes | No |
Why privacy is the real differentiator
Period data is among the most sensitive data anyone types into a phone. It records when you had sex, when you were trying to conceive, when you were pregnant, and when you stopped being pregnant. That is not a step count, and where it lives matters.
This is not a hypothetical worry. In 2021 the FTC settled with Flo Health over sharing users’ sensitive health information with third parties including Facebook and Google, despite what its policy promised at the time. Stardust scrubbed end-to-end encryption claims from its privacy policy after researchers found it was using standard server-side encryption instead, and by 2026 its policy names Meta and Google ad-measurement tools among the partners it shares activity data with. Both are legitimate products used by many people. The point is simply this: when your cycle data lives on a company’s server, its safety depends on that company’s decisions, its business model and its lawyers, indefinitely.
There is a real trade in return. Server-side data is what powers adaptive predictions, backups when you lose your phone, sync across devices, and communities of people going through the same thing. Those are genuine benefits, not marketing, and if you want them you should pick a cloud app and stop fighting it. The architectural alternative is a tool with no server at all, so there is nothing to transmit, nothing to breach and nothing to hand over. That is the category PeriodOS sits in.
1. PeriodOS - best for keeping your cycle on your own device
PeriodOS is a single HTML file you download and open in your browser. There is no login, no server and no cloud. Everything you type is saved in your browser’s local storage on that device, and Ecuato never receives it, because nothing in the file sends it anywhere.
It has seven sections. Today shows your cycle day and phase, a flow level from none through spotting, light, medium and heavy, tappable symptom chips, and a one-word mood picker (calm, tender, tired, bright, anxious, soft, fierce, quiet), plus a daily gentle reminder line. Cycle takes your last period start, cycle length and period length and returns a countdown to your next period, an estimated ovulation day, a fertile window and your current phase, alongside a three-month calendar colored by phase (menstrual, follicular, ovulatory, luteal). Flow logs intensity, color and cramping on a 1 to 5 scale, and charts the last 30 days. Symptoms is a ten-symptom library you tap to log, with a 30-day frequency chart. PMS holds a journal, self-care ritual tags, trigger notes and a running record of what helped. History tracks periods logged, your average cycle and period length, a cycle-length trend chart and an editable period log. Settings lets you export and import your data as JSON so you can back it up or move it.
It costs $23 once. No subscription, no renewal, no expiry. It opens on a laptop, adds to the home screen on iPhone via Safari or Android via Chrome, and works fully offline after the first load.
Where it loses, honestly: it does not send push notifications. It shows a countdown when you open it, but it will not ping your phone the day before your period, so if you rely on an alert, keep a calendar reminder or a mainstream app for that. There is no algorithm learning from millions of cycles; predictions are simple calendar math from your own history. There is no community, and no sync between your phone and your laptop, because the data lives on each device. Backing up is your job, and clearing your browser data clears the planner. It is a record you keep and control, not a service that thinks for you.
2. Flo - best for predictions, content and community
Flo is the biggest of these by a wide margin, and it is polished. The free tier covers ordinary cycle and symptom tracking without paying, and the prediction engine, the health library and the anonymous community forums are all strong. Flo Premium is an optional subscription, offered monthly or yearly, that adds daily personalized insights, expert-led video courses, deeper pregnancy features and a virtual health assistant.
Flo also has Anonymous Mode, a free feature that lets you use the app without attaching your name or email, so that if the company receives a request to identify you, it cannot tie the account back to you. That is a real, meaningful option and a credible response to the 2021 FTC settlement.
Where it loses: it is still a cloud service with a data-driven business, the app pushes premium upsells constantly, and Anonymous Mode reduces exposure rather than eliminating it, since your cycle data is still processed on Flo’s servers. If you want zero server involvement, this is not the tool.
3. Clue - best for clean design under EU privacy law
Clue is the quiet, well-designed one. It is based in Berlin, holds most user data in Germany, and operates under GDPR, which gives you enforceable rights to access and delete your data rather than a promise in a policy. Clue says it does not sell your data and processes health data on the basis of your consent, and its cycle-science content is unusually solid. The free version covers period and cycle tracking; Clue Plus is a subscription, typically sold yearly at around $40, that adds deeper analysis.
Where it loses: it is still a cloud account, GDPR or not, and it shares some non-health usage data with third parties for advertising unless you opt out in settings. If you want a loud, feature-packed app with a big community, Clue will feel sparse.
4. Stardust - best for astrology-minded tracking
Stardust wraps cycle tracking in astrology, tying your phases to moon cycles and horoscopes to explain your energy and moods. It is free, funded by a merchandise shop rather than a subscription, and it surged in downloads in the United States after the 2022 overturning of Roe v. Wade as people looked for alternatives. If an astrological lens genuinely helps you pay attention to your body, it is a friendly, well-made app.
Where it loses: its privacy story is rocky. It removed end-to-end encryption claims from its policy after researchers found it was using standard server-side encryption, and by 2026 its policy names Meta and Google ad tools among its data partners. It is still a cloud app, and if the astrology framing is not for you, it gets in the way of plain tracking.
5. Natural Cycles - best for FDA-cleared contraception, and only that
Natural Cycles is a different category of product from everything else here. The FDA cleared it in 2018 as the first contraceptive app, which makes it a regulated medical device with a defined intended use, and it is CE marked and hormone-free. It works from your daily basal body temperature, entered with a thermometer or pulled from a compatible wearable such as an Oura ring, and it marks which days it considers fertile. The company publishes typical-use and perfect-use effectiveness figures on its site, 93% and 98% by its own data, and those numbers are the entire point of the product. It is subscription-only, roughly $14 a month or about $107 a year, with thermometer bundles adding hardware cost on top.
Where it loses: it is a medical device, not a casual tracker, it demands daily temperature discipline to be worth anything, and it is expensive overkill if you simply want to know when your period is due. If contraception is not your goal, you are paying a medical-device price for cycle tracking you can get elsewhere. Talk to a clinician before relying on any app for pregnancy prevention.
How to choose
- Pick PeriodOS if the idea of your cycle data living on a company server bothers you, and you want one file you own forever for $23.
- Pick Flo if you want the best predictions, the most content and a community, and you are comfortable with a cloud account.
- Pick Clue if you want clean design and cloud sync but prefer your data held in the EU under GDPR.
- Pick Stardust if you enjoy an astrology lens on your cycle and do not mind a free cloud app funded by merchandise.
- Pick Natural Cycles only if your goal is contraception, and you are willing to pay a subscription and take your temperature every morning.
Predictions, and why no tracker is birth control
Every app here estimates a fertile window, but an estimate from past cycle lengths is not contraception. PeriodOS predictions are simple calendar math from your own logged cycles, useful for planning and for spotting when something is off, not for preventing pregnancy. The only tool on this list cleared to prevent pregnancy is Natural Cycles, and even that carries a real failure rate. If you want a starting window before you have any data of your own, our free period calculator and ovulation calculator give you one from your last period and cycle length, with no signup. If you are trying to conceive rather than track, our best ovulation and fertility tracking apps guide covers that case specifically. None of this is medical advice; it is a record you bring to the person who can read it.
Frequently asked questions
What is the best period tracker app?
It depends on what you weigh more heavily, features or privacy. Flo is the most complete cloud app, with adaptive predictions, symptom insights and a community, and Clue is the best-designed one under EU privacy law. If you would rather your cycle data never leave your device, PeriodOS is a $23 offline planner that keeps every entry in your own browser with no account and no server.
Is there a period tracker with no subscription?
Yes. PeriodOS is a one-time $23 purchase with no subscription, no renewal and no account. Stardust is free and funded by a merchandise shop rather than a subscription. Flo and Clue both have usable free tiers with optional paid upgrades, and Natural Cycles is the only tool here that is subscription-only with no free tier.
Which period tracker keeps my data most private?
The most private option is one with no server to leak, which is what PeriodOS is: a single HTML file that saves everything in your browser's local storage, so nothing you type is transmitted anywhere. Among the mainstream cloud apps, Clue holds most data in Germany under GDPR and says it never sells it. Flo added a free Anonymous Mode that lets you track without attaching your name or email.
Can I track my period offline with no internet?
PeriodOS can, because it is a single HTML file that runs in your browser and works fully offline after the first load. The mainstream apps need a connection to sync and load content, though most let you log a day and sync later. If offline use matters, test any app in airplane mode before you trust a full cycle to it.
Does PeriodOS predict my next period and ovulation?
Yes, using straightforward calendar math from your own history. It shows a countdown to your next period, an estimated ovulation day and a fertile window, plus a three-month calendar colored by cycle phase. These are planning estimates from your logged cycle lengths, not an algorithm trained on millions of users and not a medical prediction.
Is a period tracker app safe to use as birth control?
No. A fertile-window estimate from past cycle lengths is not contraception, and that includes PeriodOS. The only app here cleared to prevent pregnancy is Natural Cycles, which the FDA cleared as a contraceptive device, and even that has a real failure rate. Talk to a clinician before relying on any app for birth control.
What happened with Flo and privacy?
In 2021 the FTC settled with Flo Health over sharing users' sensitive health information with third parties including Facebook and Google, despite what its policy said at the time. The settlement required Flo to get affirmative consent before sharing personal health data and to have its privacy practices independently reviewed. Flo later launched Anonymous Mode as a response. It remains a legitimate app used by millions.
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