What is the difference between ACTIVE and TOTAL calories?
There are two calorie values associated with workouts on the Apple Watch or iPhone: active and total calories. The difference between these two values is actually quite simple.
Your body will burn calories no matter what. It takes energy to rest, digest, breathe and think. The number of calories your body would burn if you were doing absolutely nothing at all is your Basal Metabolic Rate, or BMR.
When you work out and elevate your heart rate your body will burn more calories than it did at rest. These 'extra' calories burned because of physical activity are your ACTIVE calories.
Your TOTAL calories, on the other hand, includes both your ACTIVE calories as well as the calories your body burns at rest during that timeframe.
For example: if your body burns 1200 calories per day as your BMR that is equivalent to 50 calories per hour. If you work out for an hour and burn 300 ACTIVE calories your body will still burn those 50 BMR calories, bringing your TOTAL calories to 350.
How are ACTIVE and TOTAL calories reported?
By default, most iPhone apps paired with a Bluetooth heart rate monitor report TOTAL (ACTIVE + RESTING) calories during a workout. .
On iPhone, the app does all the calculations based on a formula using your weight, age, gender and AVG HR.
On Apple Watch, it's completely different. The Apple Watch does all the calories calculations based on the personal information that you've entered in the Apple Watch utility app (black icon with sideways watch).
To verify these settings, open the Apple Watch utility app on your iPhone and then tap on the "My Watch" tab. You will find your personal info under the HEALTH section.