Your Apple Watch Calorie Tracker Is an Educated Guess, Not a Fact

Apple Watch and other wearables can track heart rate reasonably well, but their calorie-burn estimates are far less reliable.

The article says energy expenditure depends on many body and activity factors that wrist sensors cannot directly measure.

Studies from Stanford and other researchers found large calorie-estimation errors across devices like Fitbit, Microsoft Band, and Samsung Gear S2.

Bottom line: smartwatch calorie numbers are useful rough estimates, not precise measurements of calories burned.