Your basal metabolic rate (BMR) is the number of calories your body burns in a day when operating at absolute minimum capacity. Basically, if you sat on the couch all day long and did nothing, your BMR is how many calories your body would burn just to maintain basic activities such as heartbeat, digestion, respiration, and tissue repair.
Your BMR is influenced by a number of factors, among them age, weight, height, gender, environmental temperature, and your diet and exercise habits.
The younger you are, the higher your BMR is likely to be, since younger people have higher rates of cellular activity. In addition, men will generally have higher BMRs than women, since men usually have a greater percentage of calorie-burning lean muscle tissue in their physical makeup. Because of these variations, it is hard to pin down your BMR to the exact calorie, but we can get close. Here are gender-specific formulas for figuring out your BMR, so get your calculator ready and plug your numbers into whichever formula applies to you.
66 + (6.3 × body weight in lbs.) + (12.9 × height in inches) – (6.8 × age in years)
655 + (4.3 × weight in lbs.) + (4.7 × height in inches) – (4.7 × age in years)
Keep that calculator handy. Your basal metabolic rate only accounts for approximately 75 percent of your total daily caloric expenditure.