Garmin's Fitness Age metric explained – Gadgets & Wearables

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Garmin’s Fitness Age is a metric that lets you know how fit you are compared to your actual age. There are a couple of ways this is calculated and it depends on which watch you own.
I’ve had a Forerunner 935 for several years. In my early 50s and with a Vo2Max that fluctuated between excellent and superior for my age, the watch would tell me my fitness was the equivalent to someone in their 20s. That was very nice to hear, even if it did sound a bit unrealistic.
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In late 2021 Garmin revamped the metric for a select group of watches. Now Fitness Age is not based only on your Vo2Max, but also on several other factors. It is also not as generous when telling you how old you are fitness-wise.
Here’s everything you need to know.
As mentioned, Garmin watches measure Fitness Age differently depending on which device you own.
Older Garmin devices continue to display Fitness Age using VO2 max. This is the simplified figure that is very generous when it comes to estimating how you compare with others. This metric can fluctuate quite a bit because the only factor it depends on is your VO2Max. Basically, all that metric does is reinterpret your VO2 max score in terms of age, in order to make it more relatable. 
Perhaps this is why Garmin has revamped the metric for the latest crop of its watches to take account of Mayo Clinic recommendations. Their Fitness Age calculation takes into consideration activity intensity, resting heart rate and body fat percentage or body mass index (BMI). Lets refer to this as improved Fitness Age, or Fitness Age 2.0.
To view the metric simply go to Garmin Connect, select Performance Stats > Vo2Max > View your Fitness Age. On the web, you can find it if you go to All Activities > Vo2Max > View Your Fitness Age. On a compatible watch go to Menu > Health Stats > Fitness Age.
A benefit of the revamped calculations is that Garmin will spit out recommendations on how you can improve your Fitness Age. This could be by reducing your BMI, reducing Body Fat, increasing the number of Vigorous Days, lowering your resting heart rate and more. Below that Garmin shows which of your stats are “on target” for your age. Just keep maintaining those.
All of these contributing factors are self-explanatory and there are various things you can do to improve the metrics. It basically boils down to exercising regularly, eating well, getting enough sleep, reducing stress, maintaining a healthy weight, etc.
The smartphone app and web software will let you view 7 day, 4 week and yearly charts on how your Fitness Age has changed. This is useful for following trends.
Watches with improved Fitness Age include:
It is worth noting, you must have a Garmin Index Smart Scale (S1 or S2) to receive a body fat percentage measurement. Sure you can link up other scales to Garmin Connect but they will only sync weight, not body fat.
In that case Garmin will take your BMI into consideration instead of body fat. Which can be a bit misleading because you can have high BMI due to muscle, not fat. So for most precise Fitness Age calculations, it is recommended you link up a Garmin scale.
The other bit of bad news for those of us who have grown used to the old Fitness Age metric, is that it is not as easy to lower your Fitness Age. Garmin will spit out an Achievable Age which is up to 10 years lower than your actual age.
Which means, if you are in your 40s and 50s, no matter how hard you try Garmin will not say you have the fitness level of a 20 year old. Perhaps saying that would be a bit unrealistic, so it is just as well. I didn’t question it before because why would I not want to be as fit as someone so much younger. The improved Fitness Age metric “aged me” badly!
But this goes to show, you should not put too much stock into these types of calculations. A simple change in the way Garmin calculates the metric can vastly change your perceived Fitness Age. It is never a good idea to become addicted to these types of tools.
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I am 62 and have a Garmin 245. It tells me my fitness age is 20. So yes, it is achievable! My v02max is in the 1% for ny age .
You have a device that is on the previous version of Fitness Age. On the newer devices Garmin has changed the way it calculates the metric. If you update to the 255 or another newer device your fitness age would drastically change.
Why do you care so much?
This was a bug in earlier versions – I’m 50
And my fitness age was 21 – since I got a new garmin this went to 45
Also, this works well if you run a consistent course but doesn’t take onto account things like running hills/trails when you normally run flats, or running at elev when you normally run at sea level. My actual fitness level doesn’t change but the fitness age shows lower.
Ill stick to the old 245 for a good fitness age then. No benefit in upgrading if I read this 😉😂
Yup! 🙂 I was pretty disappointed to go from a young 20 year old to a mid-age 45 year old after upgrading to 955!!
Thanks for this interesting article. Do you also have an explanation of the calculation Garmin uses to evaluate each activity for your performance condition? I have see some pretty strange results over the years. I feel the calculation should take such factors as ambient temperature and time of day into consideration in addition to looking as pace, heart rate and heart rate variability.
Glad you enjoyed it. The newer watches do take ambient temperature and altitude into account when calculating vo2max and training status – but the older watches don’t. Here’s a link that explains:
But yes, even with that, you do sometimes get strange results!
You reference body fat and then equate it to BMI. If you are more than just average muscular, BMI can be sku’d…. Is it possible to enter body fat? My scale (although not totally accurate) indicates 12.5% but my BMI is 26.
Noone is equating body fat to BMI. As you say, the two are different. In fact, the article specifically says that using BMI “can be a bit misleading because you can have high BMI due to muscle, not fat.” Exactly what you are saying.
But Garmin uses Body Fat only if you have a Garmin Index scale. If you don’t – they use BMI because body fat will not sync with non-Garmin scales – only weight. I don’t think there’s any way to manually enter body fat.
I use an Android app called WeightLogger to manually enter metrics from my non-Garmin scales. It creates a FIT file which it then uploads to Garmin or you can do it yourself. All the metrics then appear in Connect as they would with Garmin scales. Fitness age is using the uploaded body fat value.
Thanks! Good to know there’s a workaround.
I have Garmin MK2i and it the last few days my fitness age change dramatically from 35 to 32 to 31 and today to 26. My VO2Max is 44. I’m 67 yo. My heat acclimation is 100%. My BMI is 24 and my heart rate in rest is 51.
I still wonder how can it be 26!
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