Health Age vs fitness age: what Apple, Garmin and the rest are really telling you

Your watch thinks you are 34. Your friend’s watch thinks they are 29. Someone does the maths at dinner, decides they are fitter than you, and orders a celebratory second dessert on the strength of it. The number that started that argument does not mean what either of you thinks it means.

Apple added Health Age to its Longevity tab in September 2026, joining Garmin’s Fitness Age and the body-age estimates several other platforms already show. The idea is genuinely useful. The comparison at the dinner table is not. Here is what these scores actually measure, and why yours only makes sense against itself.

One idea, several names

Strip the branding and they are the same concept: take the metrics your wearable can measure, and estimate how your body is tracking against your chronological age.

Apple’s version leans on its new higher-frequency HRV and heart data, and will fold in lab results like A1c and LDL if you add them. Garmin’s leans hardest on the VO2 max it estimates from your runs. WHOOP, Oura and others have their own takes. Same intent, four different engines.

Why the numbers disagree, on purpose

Two things make these scores personal rather than portable, and they are the same two that make recovery scores incomparable.

First, the inputs are themselves estimates that vary by brand. The biggest driver is usually VO2 max, and as we found in VO2 max across devices, the same body gets different VO2 max readings on different watches. An age score built on a number that already varies is going to vary more.

Second, each vendor picks its own reference population and its own weighting, and none of them publish either. So your Apple Health Age and your Garmin Fitness Age are two defensible estimates of the same body, and they can sit years apart without either being wrong. Putting your number next to a friend’s, on a different platform, compares two private formulas against two different references. It is noise.

What the number is actually good for

Read against yourself, over time, it is a clean signal. If your Health Age drops a year over a training block, the habits underneath it, the cardio, the sleep, the resting heart rate, are moving the right way. That is real feedback, and it is motivating in a way a raw VO2 max figure is not.

And the way to move it is not a trick. Every version of the score is a summary of the same underlying inputs, so the lever is the boring one: cardiorespiratory fitness, built by enough regular activity to clear roughly the 150 active-minutes-a-week guideline, plus decent sleep and a resting heart rate that trends down over months. Improve those and every brand’s age score follows, each on its own scale.

That scale problem is also why Fit, the cross-brand fitness competition app, never turns a fitness age into a leaderboard, and it is our app, so read that with the bias in mind. Fit ranks crews only on the units that carry between people, active minutes and distance, and leaves each person’s Health Age or Fitness Age where it belongs, on their own device as a private trend. Where Fit loses: it will not compute a body-age estimate of its own or tell you your VO2 max. Your watch does that, well, and for yourself. Fit is for the part that is actually a contest.

What to do with this

1. Track your own, over months. A Health Age or Fitness Age is a trend line for you, not a verdict against anyone else.
2. Do not compare across platforms. Your Apple number and a friend’s Garmin number are different formulas against different references.
3. Move it through the inputs. Cardiorespiratory fitness, sleep and resting heart rate; there is no honest shortcut, because VO2 max itself varies by device.
4. Compete on units, not ages. For a number to argue about with friends, argue about active minutes and kilometres.