How To Figure Out How Many Calories You Need

Your body uses energy every minute of every day. Breathing, cardiac activity, digestion and even thinking all require significant amounts of energy, which you supply through your diet in the form of calories. Calories are simply units of energy, so giving your body the exact number of calories it needs to complete its daily functions results in a perfect balance of energy in, energy out. This balance is difficult to achieve daily, but if you know how many calories your body uses, you can plan your diet accordingly. There are several ways to find this number, and each method yields progressively more accurate results.

Step 1

Use the published averages for your age, gender and activity level to get a rough idea of your daily calorie needs. The American Heart Association presents the averages as a chart, so simply cross reference your age and gender with your activity level to find your ideal caloric intake. For example, an active, 25-year-old female uses roughly 2,400 calories per day for basic body processes plus activity.

Step 2

Enter more detailed information into the U.S. Department of Agriculture's Food Planner. The USDA's calculator includes more variables, such as height and weight. It also simplifies the activity evaluation by asking if you exercise less than 30 minutes per day, between 30 and 60 minutes per day or more than 60 minutes per day. An added benefit to using the USDA calculation is that it will not only tell you how many calories you should eat, but it will recommend a meal plan with specified portions of each food group that will help you hit the target.

Step 3

Calculate your actual basal metabolic rate, or BMR, using the Harris Benedict formula. BMR is an estimate of your body's baseline needs to maintain bodily function based on the variables of height, weight, age and gender. There are free online calculators that will do the math for you or you can work out the number yourself using the formulas. For women, the basal metabolic rate is 655 + (4.35 x weight in pounds) + (4.7 x height in inches) - (4.7 x age in years). For men, the basal metabolic rate is 66 + (6.23 x weight in pounds) + (12.7 x height in inches) - (6.8 x age in years).

Step 4

Add the calories required for your activity level to your BMR. The Harris Benedict formula defines activity levels as sedentary, lightly active, moderately active, active and extra active. Each level is assigned a specific multiplier: 1.2, 1.375, 1.55, 1.725 and 1.9, respectively. Multiply your BMR by the factor associated with your activity level to determine your actual caloric needs each day.