Apple Health has a full period tracker built in. It’s called Cycle Tracking, it’s free on every iPhone, and it predicts your next period and fertile window from the dates you log. Add an Apple Watch Series 8 or later and it can also estimate, after the fact, the day you ovulated. For most people who only want dates, a prediction and strong privacy, it’s enough. A separate app makes sense if you need birth control, a group to share with, or more guidance than charts.
Everything below comes from Apple’s own support pages, its Health privacy paper and the studies Apple has published, checked in October 2026.
How does Apple Health predict your period?
From your history. Apple’s Cycle Tracking support page says predictions use the periods you’ve logged, how long they usually last and how long your cycle usually runs. When you set it up you can type in your last period and typical lengths, or confirm data another app already wrote to Health. Logging every day of each period makes the prediction better.
The fertile window is simpler than many people expect. Apple calls it a traditional calendar method. It takes the date your next period is expected and counts back 13 days for the luteal phase, then marks six days as your likely fertile window. If you log a positive ovulation test, the window shifts so that test lands on day five. Heart rate data from an Apple Watch can fine-tune it, and that option is on by default.
In the calendar, solid red circles are logged period days and red stripes are predicted ones. A light blue oval marks the fertile window and a light purple oval marks an estimated ovulation day.
How accurate is the Apple Health period tracker?
For a period prediction based on dates, it behaves like any good tracker. It’s close when your cycles are steady and drifts when they aren’t. The fertile window is the weaker part, because a fixed 13-day count assumes your luteal phase is the same length every cycle. Our guide to how accurate period tracker apps are explains why every date-based app shares that limit.
The Apple Watch estimate is the more interesting number. Apple published a study in Human Reproduction in 2025 with 262 participants who also did urine ovulation tests. In cycles where wrist temperature rose by at least 0.2°C, the estimate made during the cycle was off by about a day and a half on average. Around 80% of estimates landed within two days of the test result. Looking back over a finished cycle did a little better, at about 1.2 days. Keep two things in mind. The study was funded by Apple and most authors work there, and it didn’t produce an estimate in roughly one cycle in five.
Irregular cycles make every prediction harder. Research from the Apple Women’s Health Study found that people with PCOS, or cycles that never settled in their teens, had longer and more variable cycles in their twenties than others. The gap shrank with age. If that sounds like you, the irregular period calculator shows how wide your own range is.
How does Apple Watch estimate ovulation?
It watches your temperature while you sleep. Apple’s ovulation estimate page says the watch looks for the biphasic shift, the small rise in temperature that often follows ovulation. It then combines that with your logged periods to name the day you likely ovulated. You get a notification, and the day appears as the purple oval.
| What you need | Details from Apple |
|---|---|
| A watch with a temperature sensor | Apple Watch Series 8 or later, or any Apple Watch Ultra. The SE 3 records wrist temperature, but Apple’s ovulation page doesn’t list it. |
| Sleep tracking | Track Sleep with Apple Watch on, and Sleep Focus on for at least four hours a night. |
| Time | About five nights for a temperature baseline, then about two cycles before ovulation estimates appear. |
| Cycle Tracking set up | Fertility predictions on, and no ongoing factor such as pregnancy, lactation or contraception logged. |
| A good fit | Snug enough that the back of the watch touches your wrist all night. |
The catch is in the word retrospective. The estimate arrives after ovulation, so it can’t tell you your fertile days are coming. It mainly sharpens your next period prediction and shows you what your cycles actually do. Apple also notes that some cycles don’t show a clear rise, and that ovulation doesn’t happen every cycle. The feature is only offered in some countries. If you’re choosing a watch, our answer to does Apple Watch track periods goes model by model, the SE included.
How private is Apple Health cycle tracking?
Very, for an app that backs up. Apple’s support page says Health data other than your Medical ID is encrypted whenever your phone is locked. With two-factor authentication and a passcode, the copy synced to iCloud is end-to-end encrypted, and Apple says it doesn’t hold the key to read it. Its Health privacy paper adds that Cycle Tracking predictions are calculated on the phone, so Apple never sees your dates to work them out.
Other apps can only see your cycle data if you let them, one data type at a time. Apple’s privacy page says apps that use Health data can’t pass it on for advertising. Once an app has it, though, its own privacy policy applies. Our guide to whether period tracker apps are safe covers what to check.
Can you share Apple Health cycle tracking with a partner?
Yes. Health Sharing is a general Health feature, and cycle tracking is one of the topics you can include. In the Health app, tap Sharing, then Share with Someone, pick the person from your contacts and choose what to share. Apple’s iPhone guide walks through it, and you can change topics or stop sharing from the same tab.
The privacy paper sets the rules. You can share with up to five people, both sides need an iCloud account with two-factor authentication, and the data stays end-to-end encrypted on the way. Stop sharing and your data is removed from their device. Since they read it in their own Health app, they need an iPhone or iPad.
It works well for one partner or a parent. It’s one-way and private, and there’s nothing social about it. Each person sees your data in a separate list, and nobody sees a shared view. Our guides to sharing your cycle with a partner and sharing your period with friends compare the other ways to do it.
Apple Health period tracker not working? Fixes to try
Most problems come down to a setting or a missing log. Open Health, tap Browse, then Cycle Tracking, and work through this.
| Problem | What to check |
|---|---|
| No prediction at all | Log the first day of your last period. Predictions only start after that. Then check Period Predictions is on under Options. |
| No period or fertility reminders | Turn on Period Notifications and Fertility Notifications under Options. If your period came before the predicted date, you won’t get that cycle’s reminder. |
| Predictions feel off | Log every bleeding day, not only the first. Fix old entries that are wrong, since they feed the average. |
| No fertile window | Turn on Fertile Window Estimates under Options. Check for an ongoing factor, such as contraception, under Factors. |
| No ovulation estimate | You need a Series 8 or later or an Ultra, Sleep Focus on each night, about two cycles of data, and no ongoing factor. A loose band can spoil the readings. |
| No cycle deviation alerts | Logging a factor turns deviation detection off automatically. It works from your last six months of logs. |
Deviation detection is worth switching on if you haven’t. It reviews your last six months and can flag irregular, infrequent or prolonged periods, or persistent spotting. From there you can export a year of cycle history as a PDF to share with a doctor.
Apple Cycle Tracking vs Flo, Clue and Natural Cycles
Apple covers the basics well and charges nothing. The dedicated apps each add one or two things it doesn’t do.
| Apple Cycle Tracking | Flo | Clue | Natural Cycles | |
|---|---|---|---|---|
| Cost | Free | Free, with Premium | Free, with Clue Plus | Monthly or yearly subscription for core features |
| Apple Watch | Built-in app, temperature on Series 8 or later and Ultra | Has a watch app | Reads Apple Watch data, iPhone app only | Uses wrist temperature from Series 8 or later, Ultra and SE 3 |
| Birth control | No, Apple says not to use it that way | No | No | Yes, FDA-cleared |
Pick Natural Cycles if you want to avoid pregnancy without hormones. It’s the one here built and cleared by the FDA for that, and its App Store listing says it works with a Series 8 or newer watch. It reads your temperature each day and tells you whether you’re fertile. Apple’s estimate only looks back. Natural Cycles also reads and writes Apple Health, so your periods can show in both.
Flo suits you if you want lots of symptom insights, expert videos and Flo for Partners, its partner mode. Clue is stronger on modes for trying to conceive, pregnancy and perimenopause, and it pulls in temperature and sleep from a range of wearables. Our Flo vs Clue comparison goes deeper on those two, and does Flo sell your data covers its privacy history.
When does a separate period app make sense?
Stay with Apple if you want dates, a prediction, a fertile window and the strongest privacy of any tracker that backs up. Add an Apple Watch if you’re curious when you ovulate. Look elsewhere when you need one of these.
- Contraception without hormones. That’s Natural Cycles, and no ordinary period app.
- Guidance rather than charts, like tips for each phase or a symptom pattern explained in words. Our list of apps that show cycle phases starts there.
- Android, or a friend on Android. Apple’s tracker only runs on Apple devices.
- A group of friends who all see each other’s dates. Health Sharing is one person at a time.
The best period tracker apps guide ranks the full field if none of these fits.
Where Plum fits
Plum, a period tracker app for iPhone, is a different tool, so it’s worth being clear. Plum doesn’t read from Apple Health or write to it, and it has no Apple Watch app. Its predictions come from the dates you log, with no temperature. You sign in with Apple or Google, and your history is saved to your account so a new phone picks up where you left off.
Its sharing is invite-only groups of friends, and everyone in a group sees each other’s period days on one timeline. There’s no one-to-one partner mode. A partner can join a group like anyone else. If you want Apple Watch ovulation estimates and one partner reading your data, stay with Apple Health. Pick Plum if you want a few friends on the same screen.
