How Many Calories Does the Body Naturally Burn Per Day?

The United States Department of Agriculture (USDA) says the amount of calories you burn in a day is about 2,000, but author and nutrition professor Marion Nestle reports it's more like 3,050 calories a day for the average man and 2,400 for the average woman. The differences in these estimates make clear that knowing how many calories the normal body burns per day varies and can't easily be calculated. Equations to estimate your calorie burn exist, but they're just that — estimates. The number of calories burned in a day will vary from person to person according to size, body composition, gender, age, and amount of daily physical activity.

Here's how to estimate how many calories you burn in a day. (Image: JohnnyGreig/iStock/GettyImages)

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Calories You Burn In A Day

A calorie is simply a measurement of energy — the amount of heat required to raise the temperature of a gram of water by 1 degree Celsius, according to the National Center for Biotechnology Information. Your body uses this energy to function.

You naturally burn calories through three actions — daily living, digesting food, and physical activity, according to the book Nutritional Foundations and Clinical Applications. The caloric amount used to simply survive is known as your resting energy expenditure, or REE. Your REE is the energy needed for automatic functions, such as breathing, heartbeat, circulation, and muscle repair — and accounts for approximately 70 percent of your daily calories.

Digesting food, known as the thermic effect of food, uses about 10 percent of the energy you use in a day — so you burn calories simply by digesting the food you eat. The final portion of your calorie burn is physical activity, which is about 20 percent. Physical activity includes all functions from walking your dog to running a marathon — all burning calories in varying amounts.

Calculate How Many Calories You Need In A Day

It is possible to estimate how many calories you need and could possibly burn in a day. Common mathematical formulas help you determine this, but can vary in accuracy. Which formula you choose is largely up to personal preference. Each of these equations will find your resting energy expenditure, or basal metabolic rate.

Harris-Benedict Equation

The Harris-Benedict equation is different for men and women. For a man, compute (88.4 + 13.4 x your weight in kilograms) + (4.8 x your height in centimeters) - (5.68 x your age in years). A woman's equation is: (447.6 + 9.25 x your weight in kilograms) + (3.10 x your height in centimeters) - (4.33 x your age in years).

Mifflin-St. Jeor Equation

The American Council on Exercise and the Academy of Nutrition and Dietetics notes that the Mifflin-St. Jeor equation is more accurate for determining how many calories you need in a day. For a man, compute (9.99 x your weight in kilograms) + (6.25 x height in centimeters) - (4.92 x your age in years) + 5. For a woman, compute (9.99 x your weight in kilograms) + (6.25 x your height in centimeters) - (4.92 x your age in years) - 161.

The Harris Benedict and Mifflin-St. Jeor equations both provide calorie amounts for resting energy expenditure. They can also figure in an activity factor for a total amount of calories needed in a day. Multiply your estimate by the following:

  • 1.2 - sedentary
  • 1.375 - light exercise 1 to 3 times per week
  • 1.55 - moderate exercise 3 to 5 times per week
  • 1.725 - moderate exercise 6 to 7 times per week
  • 1.9 - physically demanding profession

Additional, more detailed formulas exist, but they require you to know the percentage of lean body mass you have. Check with an exercise physiologist or medical provider to have a body fat measurement done.

Research published in the "Indian Journal of Endocrinology and Metabolism" gives predictive equations once you know your lean body mass. The formula for the Katch-McArdle method is: 370 + (21.6 x your lean body mass in kilograms). Another method, known as the Cunningham formula, gives you a slightly higher estimate: 500 + (22 x your lean body mass in kilograms). These formulas apply to both men and women.

Average Calorie Burn Per Day

If you don't feel like doing a lot of math to figure your daily burn, you can use the chart supplied by the USDA to estimate your calories. Note that the numbers are based on the energy needs of the average man, who is 5 feet, 10 inches tall and weighs 154 pounds; the average woman in these estimates is 5 feet, 4 inches tall and 126 pounds.

The USDA chart uses an estimation of activity level. Use the following to determine which is right for you:

  • Sedentary: Light activity - walking to and from your car, making dinner
  • Moderately Active: Those who have daily movement equal to 1.5 to 3 miles per day
  • Active: Physical activity that's equal to walking more than 3 miles per day.

The average daily calorie burn for a man between the ages of 31 and 50 is 2,200 to 2,400 if he's sedentary; 2,400 to 2,600 if he's moderately active; and 2,800 to 3,000 calories if he's considered active. For sedentary women, also between the ages of 31 to 50, the average calorie burn is 1,800 per day; for moderately active women, it's 2,000 calories; and for active women, it's 2,200 calories per day.

People who are larger or smaller than the average person used to determine these ranges will burn a different amount of calories. Younger people tend to burn more than these estimates, while older people tend to burn fewer calories. The estimates don't accurately take into account intensity of daily activity, genetics, or body composition.

Calorie Quality

For years, medical professionals have taught that a calorie is a calorie, however, it turns out, this is not the case. Even though two people can eat the same amount of calories, the quality of those calories is more predictive of health, according to the National Center for Biotechnology Information. Not all foods affect the body in the same way, so choose your calories wisely.

If you are curious how many calories you are eating in a day, try using a daily calorie tracker, such as MyPlate Calorie Counter. Once you have an estimate of how many calories you burn in a day, you can then project how much you should eat to either maintain, lose, or gain weight.

Keep track the best you can to stay in line with your calorie needs. If the scale starts to creep up, you know you're probably eating more than your body needs and that you should trim portion sizes slightly and exercise more.

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