The basal metabolic rate is the amount of calories needed to maintain basic body functions, such as breathing or heart beats.
When I estimate my caloric needs, I generally start with the sedentary amount and add in any added activity. For example, my BMR is approximately 2100 calories. Then I might burn a few hundred calories by walking a few miles during the day. A two hour pickleball session might burn 1000 calories. Overall, this is just an estimate but an important step to understanding how many calories you need to consume to maintain your current weight.