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How do I know how many calories I need per day?

Dr. Vonda Wright, MD
Orthopedic Surgeon

There is a classic equation for predicting how much energy you need just to survive, or your basal metabolic rate (BMR). It is called the Harris Benedict Equation and uses sex, weight, height, and age to predict your energy requirements.

  • Women: BMR = 655 + (4.35 X weight in pounds) + (4.7 X height in inches) – (4.7 X age in years)
  • Men: BMR = 66 + (6.23 X weight in pounds) + (12.7 X height in inches) – (6.8 X age in years)

For example, for a 40-year-old woman who is 64 inches tall and weighs 116 pounds: BMR = 655 + (4.35 X 116 pounds) + (4.7 X 64 inches) – (4.7 X 40 years) = 1272.4

Then, to determine your total calorie needs to maintain your current weight, multiply your BMR by your activity factor:

  • Sedentary (little or no exercise): BMR X 1.2 = daily calorie needs
  • Lightly active (light exercise one to three times a week): BMR X 1.375 = daily calorie needs
  • Moderately active (moderate exercise three to five times a week): BMR X 1.55 = daily calorie needs
  • Very active (hard exercise six to seven times a week): BMR X 1.725 = daily calorie needs
  • Extra active (very hard exercise/sports/physical job): BMR X 1.9 = daily calorie needs

For example, for a 40-year-old woman who is 64 inches tall, weighs 116 pounds, and does five days of moderate exercise per week: BMR X 1.55 = 1272.4 X 1.55 = 1972.2 calories a day to maintain her current weight.

If she were a couch potato, the same woman could only eat 1526.8 calories per day without gaining weight.

This formula is good for most people but underestimates the energy needs of a highly muscular person since muscle burns more energy just for cells to function without doing any extra activity. The formula also overestimates the calories of a fat person since fat burns less energy for normal metabolism.

Fitness After 40: How to Stay Strong at Any Age

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Fitness After 40: How to Stay Strong at Any Age

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You can get a rough estimate of how many calories you need each day to maintain your weight by simply multiplying your weight in pounds by 15. But, the amount of calories you need depends on your age, height, weight, muscle mass, and activity level. To get a good estimate, go to the USDA's interactive tool (fnic.nal.usda.gov/interactiveDRI) for calculating daily caloric needs.
Your calorie needs depend on your:
  • body size
  • age
  • height
  • weight
  • activity level
  • gender
  • other conditions, such as being pregnant
Determine your activity level. Before you check out a calorie chart, choose which statement best describes your current activity level:
  • I don't do anything other than what I need to do for my usual activities, such as going to work or school, grocery shopping, or doing chores around the house. (This is considered not active.)
  • I do some moderate exercise every day in addition to doing my usual activities. For example, I walk about 1.5 to 3 miles a day at about 3 to 4 miles an hour. Or I do something else that's moderately active. (This is considered moderately active.)
  • I am very active every day in addition to doing my usual activities. For example, I walk more than 3 miles a day at about 3 to 4 miles an hour. Or I do something else that's very active. (This is considered very active.)
Next, find a calorie chart that includes activity levels and find the line on the calorie chart that applies to you based on your gender, age, and level of activity. Remember that the chart estimates how many calories you should eat per day to keep your body weight where it is now.

If you want to lose weight, you may need fewer calories. You should talk with your health care team for more personalized recommendations, but the chart can help you get started.

If you have gained weight over time, it is because on average you are eating more calories than your body burns off. Extra calories add up over time and will turn into extra pounds.

One pound is equal to 3,500 calories. So, if you want to lose 1 pound per week, you would need to cut 500 calories from the calories that you usually eat in a day.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.