If you are trying to lose weight, you have to burn more calories than you eat. As a matter-of-fact, to lose one pound per week, you have to have a daily calorie deficit of 500 calories. But you first have to figure out how many calories you should be eating to maintain your current weight. The first step in finding out is to calculate your Basal Metabolic Rate or BMR.
Basal Metabolic Rate
Knowing your BMR will give you the number of calories you need each day to sustain normal bodily functions like breathing keeping your heart beating. To lose weight, you have to either burn off or avoid eating the extra calories your body does not need.
To calculate your BMR, you have to factor in your height, weight, age and sex. For women the formula is 655 + (4.3 x weight in pounds) + (4.7 x height in inches) – (4.7 x age in years); for men 66 + (6.3 x weight in pounds) + (12.9 x height in inches) – (6.8 x age in years).
For example, let’s calculate the BMR on a 30-year old female 5 ft. 5 in, tall and weighing 150 pounds. Plugging the numbers into the formula 655 + (4.3 x 150) + (4.7 x 65 inches) – (4.7 x 30), we find she should be eating about 1,464 calories per day to maintain her current weight.
Note the formulas are based on a normal adult body. If you are extremely muscular or very obese, then your resulting figures will be underestimated or overestimated, respectively.
Factoring In Your Activity Level
Because how much activity you do in a day affects how many calories you burn, you have to adjust the number of calories in your BMR. If you are basically inactive most of the day, then multiply your BMR by 20%. If you exercise most days, use a 40% figure. For those that are very active, multiply your BMR by 50%.
Taking our example from above and adding in the 40% additional calories needed to support her activity level, the total number of calories she needs to maintain her weight while exercising most days is now 2,049.
Cutting Calories for Weight Loss
Keeping in mind a one pound per week weight loss, our example would have to cut 3,500 calories per week from her current diet. Break that down per day, and she should be eating 1,549 calories.
If you find you are losing more than one pound per week, you may want to add back in a few calories. If you are not losing at least some weight per week, consult your doctor for further guidance.