Fitness age
Your fitness age on
Apple Watch.
There is no screen that says "fitness age" - but your watch is already measuring the ingredient. Here is where it hides.
If you have a Garmin in your past, you are used to a single tidy number: your fitness age. Open the app, and there it is, telling you your body performs like someone five years younger or eight years older. So you got an Apple Watch, went looking for the same thing, and came up empty. There is no screen on Apple Watch that says "fitness age."
That is not a missing feature so much as a missing label. Your fitness age apple watch number is already half-built: your watch is measuring the exact signal a fitness age comes from. It just hands you the raw ingredient under a different name and stops short of turning it into an age. Once you know where to look, the number is right there, and turning it into your fitness age is the easy part.
The signal you are after is called Cardio Fitness, and it is Apple's estimate of your VO2 max.
What Apple Watch actually measures: Cardio Fitness.
VO2 max is the single most studied marker of whole-body fitness and one of the strongest predictors of long-term health that exists. It is the peak rate at which your body can take in and use oxygen, and it falls naturally with age unless you train against the slide. Garmin reads it, turns it into a fitness age, and shows you the age. Apple reads the same thing, calls it Cardio Fitness, and shows you the raw estimate plus a plain label - low, below average, above average, or high for your age and sex.
So Apple Watch is not behind here. It is quietly doing the hard part: estimating your VO2 max in the background from your heart rate during everyday walks, hikes, and runs outdoors. What it does not do is take the last step and translate that estimate into the one framing people actually find motivating, the age.
That last step is the whole game, because a VO2 max figure means almost nothing to most people, while "your heart and lungs perform like someone seven years younger than you" lands instantly.
Where to find your Cardio Fitness number on iPhone.
You do not check this on the watch face. It lives in the Health app on your iPhone. Here is the path:
- Open the Health app on your iPhone.
- Tap Browse at the bottom right.
- Tap Heart.
- Scroll to and tap Cardio Fitness.
There you will see your current Cardio Fitness estimate, its level for your age and sex, and a trend over time. If the section is empty, your watch has not gathered enough outdoor walking, hiking, or running data yet. A few brisk outdoor walks with the watch on, arms swinging freely, and it will start filling in.
One thing worth knowing: Apple records this in the background, so the number reflects your real movement, not a one-off treadmill test. That makes it honest, but it also makes it easy to ignore, because nothing on your wrist ever surfaces it.
Turning Cardio Fitness into a fitness age.
Here is the translation Apple leaves out.
A fitness age compares your VO2 max against the typical values for people of different ages and the same sex. If your Cardio Fitness matches the average for a 40-year-old and you are 48, your fitness age is roughly 40 - your cardiorespiratory system is performing eight years younger than your birthday. If it matches the average for a 55-year-old, the gap runs the other way, and that gap is the signal worth acting on.
The science underneath this is well established. The reference curves come from large population studies of VO2 max across age and sex, most notably the HUNT study out of Norway, which tracked the fitness of tens of thousands of people and produced the age and sex norms that fitness-age calculations lean on. This is why the framing is trustworthy rather than gimmicky: it is your measured oxygen uptake, read against a real population, not a wellness score invented from thin air.
The reason Apple Watch does not show you this is a product choice, not a data gap. The data is sitting in Apple Health. It only needs to be read and translated.
Why the number is worth watching.
A fitness age is motivating in a way a raw VO2 max value never is, and it is responsive in a way your chronological age never is. Your birthday only goes one direction. Your fitness age can move both. Steady aerobic work, more daily movement, better sleep and recovery, and it drifts younger. Months on the couch, and it drifts older. It is one of the few longevity-relevant numbers you can genuinely change, and watching the trend is more useful than any single reading.
The honest caveat is the same one that applies to Garmin: this is an estimate from wrist heart rate, not a lab test with a mask and a treadmill. Treat the trend as the truth and the exact figure as a close approximation, and it will serve you well.
Reading the number your watch already has.
If your Apple Watch has the ingredient and Apple just does not plate it as an age, the work left is small: read Cardio Fitness out of Apple Health and translate it against the population curves into a fitness age you can track.
That translation is one of the things Body Insights does. It reads your Cardio Fitness from Apple Health and reads it against your age and sex, so the fitness age your Apple Watch was always capable of producing finally shows up as a number you can watch move - against your own past self, not a stranger. Your watch tracks the oxygen. We translate it into the age.
If the gap between your fitness age and your real age is what you are really chasing, the next piece is what that gap actually means - and how to close it.