How Many Calories Do I Need Each Day?

Using the Harris-Benedict Formula

Knowing how many calories you need to consume each day is essential for losing, gaining, or maintaining weight. One way to determine this with a technique called the Harris-Benedict formula.

The Harris-Benedict equation is a method used to estimate a person's basal metabolic rate (BMR). By definition, BMR is your rate of metabolism (the conversion of calories and oxygen to energy) at rest. It is the minimum level of energy required to sustain vital functions such as breathing, digestion, and circulation.

The Harris-Benedict formula is often used to assist weight loss by ensuring that you reduce the intake of calories below what you need to maintain weight.

Calculating Your Daily Calories

The Harris-Benedict formula is used to describe your basal metabolic rate (BMR) as a numeric value. Your BMR is determined by your sex, age, and body size, and calculating this number tells you how about how many calories you burn just being alive and awake.

The formula for the BMR is quite complex:

Step One: Calculate Your BMR

  • For women, BMR = 655 + (4.35 x weight in pounds) + (4.7 x height in inches) - (4.7 x age in years).
  • For men, BMR = 66 + (6.23 x weight in pounds) + (12.7 x height in inches) - (6.8 x age in years).

Once you get out of bed and begin to move around, you will need to adjust this figure as you expend more energy. This value, called active metabolic rate (AMR), is calculated by multiplying your BMR by an assigned number representing the various activity levels. This number ranges from 1.2 for being sedentary up to 1.9 for being very active.

Calculate your AMR multiplying your BMR and by your current level of activity:

Step Two: Calculate Your AMR

  • Sedentary (little or no exercise): AMR = BMR x 1.2
  • Light active (exercise 1-3 days/week): AMR = BMR x 1.375
  • Moderate active (exercise 3-5 days/week): AMR = BMR x 1.55
  • Active (exercise 6-7 days/week): AMR = BMR x 1.725
  • Very active (hard exercise 6-7 days/week): AMR = BMR x 1.9

Your AMR represents the number of calories you need to consume each day to stay at your current weight. If you want to lose weight, you need to increase your level of physical activity or decrease your caloric intake by eating less.

How to Use This Information

For the purpose of weight loss, the AMR provides you the means to figure out how many calories you either need to exclude, how many calories you need to burn through added exercise, to lose a specific amount of weight.

For example, if your BMR is 1,400 (the average for American women) and you are moderately active, your AMR would be 2,170 (1,400 x 1.55). Since a pound of fat is equal to 3,500 calories, you would need to cut 500 calories per day to lose a pound per week. This is called your calorie deficit.

If you plan to lose weight simply by diet, your daily calorie intake would be 1,670 (2,170 - 500 = 1,670). If you plan to do it by exercise alone, you would need to burn 500 calories each day above and beyond what you already do. For this reason, a combination of diet and exercise almost always achieves the best result.

Test Accuracy

Unfortunately, the Harris-Benedict formula isn't exactly perfect. According to the Academy of Nutrition and Dietetics, research studies have indicated the formula is about 90 percent accurate around 60 percent of the time.

That means it could be way off about 40 percent of the time, which is rather disheartening. Even worse, when the formula was wrong, it overestimated the calorie needs of the research subjects, so they were burning fewer calories than they thought.

The problems may be due to physical or genetic factors that impede or enhance metabolism in some people. Moreover, there's a good chance that many people overestimate how physically active they are.

Despite these shortcomings, the Harris-Benedict formula provides you with a relatively good picture of your general caloric needs. If you don't achieve weight loss based on the calculations, simply adjust your daily calorie count up or down or recalculate your AMR based on a lower activity level.

Never consume less than 1,200 calories per day without medical supervision. Doing so can send your body into starvation, slowing metabolism and increasing the risk of gallstones, gout, fatigue, irregular periods, and malnutrition.

A Word From Verywell

Though it really isn't difficult to grab a calculator and figure this all out by hand, there are plenty of online calculators that shortcut the process. Online calorie calculators make the perfect starting place for anyone who wants to get their calorie counts under control.

You can also find nutritional calculators and exercise calculators that keep track of the calories you burn each day.

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