ExerciseCaloriesAndWeightLoss.com

'How many calories should I eat a day?' is a common question, although there is no single pat answer that applies to everybody. The amount of calories you should eat a day depends on many factors. These include your current weight, height, age, gender, and activity level. It also depends on your goal: whether you want to maintain, lose or gain weight.

You can calculate the number of calories you should eat a day using two different formulas that take all the variables in to account. The first formula, known as the Harris-Benedict equation, takes care of answering "how many calories should I eat a day" to maintain your body's functioning, or your basal metabolic rate, or BMR. The second formula calculates any additional calories you may need, or not need, based on your activity level, or active metabolic rate, or AMR.

Harris-Benedict Formula

The Harris-Benedict formula is different for men than it is for women, although both use numbers based on your weight in pounds, your height in inches, and your age in years. The equation for men adds up three numbers then subtracts a fourth number. The numbers you need to add up are the number 66; your weight multiplied by 6.23; and your height multiplied by 12.7. Your fourth number, which you subtract from the sum of the first three numbers, is your age multiplied by 6.8. The formula for a 40-year-old man who weighs 200 pounds and is 6-feet tall would look like this, for example: 66 + (200 x 6.23) + (6 x 12.7) – (40 x 6.8).  Calculate the equation and the amount of calories necessary to stay alive is 2278.

For women, the numbers to add are the number 655; your weight multiplied by 4.35; and your height multiplied by 4.7. Your fourth number, which you subtract from the sum of the first three numbers, is your age multiplied by 4.7. The formula for a 40-year-old woman who weighs 130 pounds and is 5 feet, 6 inches tall would look like this: 655 + (130 x 4.35) + (5.5 x 4.7) – (40 x 4.7). Calculate the equation and the amount of calories necessary to stay alive is 1560.

Acive Metabolic Rate

If you did nothing other than lie there breathing, the Harris-Benedict formula would be the end of the calculations. But most of us move around at least a little bit, which is where the second equation of AMR comes in. To calculate your AMR, or how many calories you need per day based on your activity level, you need to multiply your BMR by one of five numbers. If you never or rarely exercise, the number is 1.2. If you workout lightly one to three days a week, the number to use is 1.375. If you are moderately active, working out about three to five days per week, use the number 1.55. If you workout six to seven days a week with hard exercise, use the number 1.725, and if you workout six to seven days a week with very hard exercise, use 1.9.

That means a very active man from the example above would multiply his total of 2278 by 1.9 to come up with the calories he would need to maintain his weight with a very high activity level, or about 4328. If he were instead inactive, he would multiply his total of 2278 by 1.2 to maintain his weight with a fairly sedentary lifestyle, or about 2734.

Goals

Your question of “How many calories should I eat a day” is then answered, based on the above formulas, if you are happy maintaining your current weight. If you’d rather lose or gain weight, however, you need to make adjustments. Each pound is worth 3500 calories, which means you will gain a pound for every 3500 calories you eat above your daily calorie count and lose one pound for every 3500 calories you expend below your daily calorie count.

Weight loss and weight gain are not achieved in a day or two, but rather over a steady decrease or increase in calories over a certain amount of time. The general rule for healthy weight loss is to lose about 1 pound a week, which means a decrease of 3500 calories over a seven-day period, or 500 calories a day. Another healthy rule is to eat no fewer than 1200 calories per day. Increasing your activity level and exercise can speed up weight loss by burning additional calories.