The number of calories you burn to maintain body functions is your resting metabolic rate (RMR).
It is determined by measuring your body's oxygen utilization while you are at rest - usually first thing in the morning. Your resting metabolic rate typically accounts for about 65-75 percent of your total daily calorie expenditure.
Resting metabolic rate decreases with age and with the loss of lean body mass. Increased cardiovascular exercise and muscle mass can increase your RMR. Illness, pregnancy, crash dieting , previously consumed food and beverages, environmental temperature and stress levels can affect your overall energy expenditure an in turn affect your resting metabolic rate.
RMR is measured by gas analysis but a rough estimation can be acquired through an equation using age, sex, height, and weight. Here is an equation that you can use to figure out your RMR:
Males: 66+ (6.22 x weight (lbs)) + (12.7 x height (inches)) - (6.8 x age)
Females: 655 + (4.36 x weight (lbs)) + (4.32 x height (inches)) - (4.7 x age)
To increase your RMR, try to include both cardiovascular and strength training activities in your exercise program. Try to exercise 2-4 times a week and consult with a personal trainer to help you will form and technique.