Fitness age on Apple Watch: where to find it and how to read it

Updated October 29, 2026 · 7 min read · How we write these

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Short answer

Apple Watch does not show a fitness age by name. It estimates your VO2 max, which Apple calls Cardio Fitness, and that is what every fitness age is built from. On iPhone, open Health, tap Browse, Heart, Cardio Fitness. Tap the info button in the corner to see the average level for every age, then find the age whose average matches your number: that is your fitness age. Apps such as Fitness Age read the same value from Apple Health and do the lookup for you.

A friend says their fitness age is 31, ten years under their real one, and that it came from their Apple Watch. You scroll through every screen on your own watch and find rings, workouts and a heart rate, but nothing called fitness age.

What a fitness age actually is

A fitness age is one number translated into years. The number is VO2 max: the most oxygen your body can use during hard exercise, written in millilitres per kilogram of body weight per minute (mL/kg/min). It falls as people get older. In the Norwegian HUNT3 Fitness Study, which NTNU's CERG research group uses for its own fitness calculator, maximal oxygen uptake was about 7% lower with every 10 years of age.

That steady slope is what makes the trick work. Take your VO2 max, find the age at which that value is the average, and call it your fitness age. If your VO2 max is typical for people ten years younger, your fitness age is ten years under your real one. If it is typical for people older than you, it runs the other way.

So a fitness age contains nothing your VO2 max does not. It just puts it on a scale people already understand. It also ignores sleep, resting heart rate on its own, HRV and everything else that apps fold into a "biological age". Those are a different kind of score, compared in our guide to biological age apps for Apple Watch.

Where Apple Watch keeps the number

Apple Watch does not show a fitness age by name, on the watch or on the iPhone. What it records is the input: an estimated VO2 max, which Apple calls Cardio Fitness. Apple says the watch estimates it during Outdoor Walk, Outdoor Run and Hiking workouts by measuring how hard your heart works, and factors in your age, sex, weight, height and any medications you have entered that might affect your heart rate. It needs Apple Watch Series 3 or later.

To see it on iPhone:

  1. Open the Health app.
  2. Tap Browse, then Heart, then Cardio Fitness.
  3. Tap Show All Cardio Fitness Levels to see where you sit for your age and sex.

That last screen sorts you into one of four ranges: Low, Below Average, Above Average or High. Apple says the ranges are based on data from FRIEND, the Fitness Registry and the Importance of Exercise National Database, a US registry of lab exercise tests. The ratings are only shown to users aged 20 or older, and the watch supports VO2 max values from 14 to 65 mL/kg/min.

If the screen is empty, that is usually the workouts. Apple says a first estimate takes at least 24 hours of wear followed by several outdoor walks, runs or hikes. Indoor workouts, treadmills and gym equipment do not count. Apple's 2021 white paper on the feature adds that the estimate comes from walking, running or hiking on fairly flat ground (under a 5% grade) with a good GPS and heart rate signal and enough effort to raise your heart rate. A slow dog walk on a hilly street may never produce one.

How to read your fitness age off the Health app

The step most guides skip: the Health app already has the table you need. On the Cardio Fitness screen, tap the info button in the upper corner (some regions label it Show information). Apple says it shows the average cardio fitness levels for all ages, for Female, Male or All.

  1. Note your latest VO2 max at the top of the Cardio Fitness screen.
  2. Tap the info button and pick the option that matches the sex in your Health Details.
  3. Find the age whose average is closest to your number. That is your fitness age.

Two checks before you trust it. First, your real age, sex, height and weight all feed the estimate, and they come from Health Details: tap your profile picture or initials in Health, tap Health Details, then Edit. A wrong birth year shifts both the estimate and the comparison. Second, Apple warns that conditions or medications that limit your heart rate can make the watch overestimate VO2 max, which would make your fitness age look younger than it is. Apple's cardio fitness support page covers how to tell the Health app about them.

The watch can also send a notification if your level falls into Low for your age and sex. For users aged 20 to 59, Apple's white paper says that threshold is the lowest fifth of the FRIEND data for your sex and decade. A notification is a prompt to look at the trend, not a diagnosis; if it worries you, talk to a doctor.

Why your fitness age may read older than it should

Apple Watch is good at heart rate, but VO2 max from a wrist is an estimate, and independent studies say it tends to read low.

That matters more for a fitness age than for the raw number. If fitness drops by roughly 7% a decade, an error of around 13% can move a fitness age by more than ten years. Both studies are small, so this is not the last word. But it is a good reason to read the trend over months, in the 6M or Y view, rather than celebrate or panic over one reading.

Apps that do the lookup for you

If you would rather not read a chart, a few App Store apps take the Cardio Fitness value from Apple Health and convert it. Check each one's In-App Purchases list before granting Health access.

Apple's own age score, Health Age, will use VO2 max alongside resting heart rate, sleep and HRV, but it is not in iOS 27.2. Our guide on how to see Apple Health Age tracks where it stands.

Where Nularo fits (and where it does not)

Nularo is an iPhone app with a creature that lives on your Apple Health data, and its Age tab shows a Creature Age. To be upfront: it is not a fitness age. It does not use VO2 max. It is recalculated every week from six habits: sleep duration (anchored at 7h30 a night), bedtime consistency, steps (8,000 a day), active minutes (30 a day), resting heart rate and HRV.

That makes it the other half of the picture. A fitness age tells you about your engine. Creature Age tells you about the week you put it through, with a per-habit breakdown of which one added years. A good stretch can make the creature up to 1.5 years younger than you, and it stays hidden until 7 days of data exist. It reads everything from Apple Health on its own, so there is nothing to log. If HRV is the habit dragging it up, read why Apple Watch HRV is always low before you believe it.

Nularo's Age tab: a Creature Age of 27.9 against a real age of 22, with the age history graph
Nularo's Age tab: a Creature Age of 27.9 against a real age of 22, with the age history graph.

The honest limitations: Creature Age is a rules-based, for-fun number built from public-health guidelines, not a medical measurement. Nularo is iPhone only, without an Apple Watch the heart and sleep data behind it gets thin, and it reflects last week rather than today. It judges, it does not coach. It is a subscription, $39.99 a year with a 3-day free trial or $9.99 a month. If you want something that reacts to your data more like a pet than a score, see our list of virtual pet apps that use Apple Health.

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Frequently asked questions

Does Apple Watch tell you your fitness age?

Not by that name. It estimates your VO2 max, shown as Cardio Fitness in the Health app, and rates it as Low, Below Average, Above Average or High for your age and sex. The info button on the Cardio Fitness screen shows the average level for every age, which is all you need to read off a fitness age yourself.

Why does my Apple Watch not show Cardio Fitness?

Apple says the watch needs at least 24 hours of wear followed by several Outdoor Walk, Outdoor Run or Hiking workouts before a first estimate. Indoor workouts and gym equipment do not count. It needs Apple Watch Series 3 or later, and the Low to High ratings only appear for users aged 20 or older.

Is my Apple Watch fitness age accurate?

Treat it as a rough guide. Two independent studies found Apple Watch read VO2 max about 6 mL/kg/min lower than a lab test on average, with errors around 13%. In the 2026 study, the watch put only 14% of participants in their correct fitness percentile band. A lower reading makes the fitness age look older.

Is fitness age the same as biological age?

No. Fitness age only translates one number, VO2 max, into an age. Biological age apps combine several metrics, and lab tests such as epigenetic clocks measure something else entirely. If any of these numbers worries you, talk to a doctor.

Does Nularo show a fitness age?

No. Nularo's Creature Age is built from sleep duration, bedtime consistency, steps, active minutes, resting heart rate and HRV. It does not use VO2 max, so it is a habits number rather than a fitness age, and it is a rules-based, for-fun estimate, not a medical one.

Nularo is an entertainment and wellness app, not a medical device. Nothing on this page is medical advice. If something about your sleep or heart worries you, talk to a doctor.

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