Garmin and Polar total calorie discrepancy

Interesting. If this kind of difference (over 10%) is considered normal (which I gather from responses to this post) than calorie burned is more of an arbitrary number than correct value. Good to know.

Note the word "estimate" and "group" which means any algorithm will have to make adjustments for age, physiology etc etc - and different people, using different algorithms, will skew it in different ways

https://www.runnersworld.com/training/a20796192/how-accurate-is-your-wearables-calorie-count/

Its factored off of a wide range of physiological metrics - Vo2 is used

Without getting too deep in the weeds, smartwatches, like the Garmin Forerunner 955 Solar I use, estimate energy expenditure (EE) utilizing the wearer’s heart rate data, respiration rate, oxygen consumption, and the personal information you enter (gender, age, height, and weight).

VO2 max, or the maximal oxygen uptake an individual needs to perform aerobic work, is a metric used in determining EE. Ideally, VO2 max would be collected in a laboratory setting. Smartwatches, like Garmin’s, use the personal information you provide plus your heart rate and speed of the activity (for exercise like running or walking). Accuracy of this method has its limitations because of outside variables, such as the type of terrain you’re running on and the amount of wind.

And Polar and Garmin definitely offer different values for VO2

The moral of this story, embrace its not as accurate as we'd like and use one app and stick to it.

Do the Polar VO2 test and the Garmin one. if they disagree, there may be part of it. There's a load of different factors on calorie burnt in activities.

One thing you could also do is track the discrepancy over time - does the difference stay static, or does it vary...

EDIT - I just realised as the article says, respiration is involved. Garmin gets that indirectly from HRV, but it looks like Polar Flow doesnt have respiration data in that summary, does it?

INterestingly while looking I found this

https://wellwisp.com/is-garmin-calorie-burn-accurate/

NOW - while I do urge caution in that wed need to find its sources, it does say this.. which may also factor in and may be what you're seeing

Table 3: Garmin vs. Other Trackers (Accuracy Variations)