Harris-Benedict Calculator

The Harris-Benedict calculator estimates your basal metabolic rate, the calories your body burns at complete rest, and then multiplies it by an activity factor to give your daily calorie needs. Example: a 35-year-old man at 5 ft 10 in and 180 lb has a Harris-Benedict BMR of 1,837 calories, or about 2,847 calories a day when moderately active.

Three sister tools cover neighboring questions. The BMR Calculator runs the same idea through the modern Mifflin-St Jeor equation, the TDEE Calculator focuses on the activity multiplier step and total daily burn, and the Calorie Calculator turns a maintenance number into a goal-based target. Use this page when you specifically want the Harris-Benedict number, either because a coach, a textbook or an older app asked for it, or because you want to see how the classic equation compares with the modern one.

How the Harris-Benedict equation works

The equation is a linear regression: it adds a fixed constant, adds calories for every kilogram of body weight and every centimeter of height, and subtracts calories for every year of age. Separate coefficients are used for men and women. The revised version published by Roza and Shizgal in 1984 is the default here:

where W is body weight in kilograms, H is height in centimeters and A is age in years. The result is calories per day at rest. Because the calculator is imperial-first, you can enter pounds and feet plus inches; the conversion to metric happens internally, so nothing is lost.

Translated into US units, the coefficients say something simple: each extra pound of body weight adds about 6.1 calories a day for men and 4.2 for women, each extra inch of height adds about 12.2 calories for men and 7.9 for women, and each decade of age subtracts about 57 calories for men and 43 for women.

Worked example: a 35-year-old man

Take a man aged 35, 5 ft 10 in tall, weighing 180 lb. First convert: 180 lb is 81.647 kg, and 70 inches is 177.8 cm. Now run the male coefficients:

• Constant: 88.362
• Weight term: 13.397 × 81.647 = 1,093.8
• Height term: 4.799 × 177.8 = 853.3
• Age term: 5.677 × 35 = 198.7, which is subtracted

Adding the first three and subtracting the fourth gives 1,837 calories per day as his basal metabolic rate. If he is moderately active (exercise three to five days a week), his maintenance level is 1,837 × 1.55 = 2,847 calories. To lose about a pound a week he would eat roughly 2,347 calories a day; to gain at the same pace, roughly 3,347.

From BMR to daily calories: the activity multipliers

BMR alone is not an eating target. It only covers the energy your organs use lying still, which is roughly 60% to 70% of what most people burn. The Harris-Benedict system pairs the BMR figure with a multiplier for everything else you do: walking, working, training and digesting food. Applied to the 1,837-calorie example above:

Notice the spread: the same man is predicted to need 2,204 calories if he sits all day and 3,490 if he trains hard and works on his feet. That 1,286-calorie range is far larger than the difference between competing BMR equations, which is why picking an honest activity level matters more than picking the perfect formula.

Second worked example: a 42-year-old woman

Now a woman aged 42, 5 ft 5 in tall, weighing 150 lb. That is 68.039 kg and 165.1 cm. Using the female coefficients: the weight term is 9.247 × 68.039 = 629.2, the height term is 3.098 × 165.1 = 511.5, and the age term is 4.330 × 42 = 181.9. Starting from the constant 447.593 and combining gives a BMR of 1,406 calories per day.

If she is lightly active, her maintenance level is 1,406 × 1.375 = 1,934 calories, and a 500-calorie deficit puts her at about 1,434 calories a day for roughly a pound of loss per week. That target sits above her BMR, which is exactly what you want: a deficit taken out of the activity portion of her budget rather than out of the energy her organs need.

Harris-Benedict BMR by weight and age

The table below applies the revised male equation at a fixed height of 5 ft 10 in, so you can see how weight and age pull the number in opposite directions.

The same grid for women, at a fixed height of 5 ft 5 in, runs lower and flatter because the female coefficients for weight and height are smaller:

Harris-Benedict vs Mifflin-St Jeor

The Mifflin-St Jeor equation, published in 1990, is the formula most dietitians use today because validation work found it more accurate for the general population. Harris-Benedict usually predicts a little higher. The table compares all three equations across six profiles, computed with the same converted metric inputs:

The gap column is revised Harris-Benedict minus Mifflin-St Jeor. Across these profiles it runs from 49 to 104 calories a day, roughly 3% to 7%. Multiplied by an activity factor of 1.55 that becomes 76 to 161 calories on the daily target, which is real but small next to the error in guessing an activity level. If you want the modern number instead, the BMR Calculator runs Mifflin-St Jeor directly.

Revised 1984 vs original 1919 coefficients

Harris and Benedict published their study in 1919 from a small sample of healthy adults measured with early calorimetry equipment. Roza and Shizgal reworked the coefficients in 1984 against a much larger dataset, producing the version this calculator uses by default. In practice the two rarely disagree by much for adults of typical size: our 35-year-old man is predicted at 1,837 calories by the revised equation and 1,842 by the original, about 6 calories apart, and the 42-year-old woman comes out at 1,406 versus 1,415, about 8 apart. The original equation weights height and age more heavily, so the two versions drift further apart at the extremes of height and at older ages. Switch modes in the calculator if a specific textbook, exam question or clinical protocol asks for the 1919 figures.

How to use this Harris-Benedict calculator

1. Pick your units. US units accept pounds and feet plus inches; metric accepts kilograms and centimeters. Conversion happens behind the scenes, so both give the same answer.
2. Enter sex, age, height and weight. Use your current scale weight, not a goal weight, and your real age rather than how old you feel.
3. Choose the equation version. Leave it on revised (1984) unless something specifically asks for the original 1919 coefficients.
4. Select an activity level. Be conservative. Desk work plus three gym sessions a week is normally lightly or moderately active, not very active.
5. Read the result. The headline number is your BMR. The tiles beneath show your maintenance calories, the Mifflin-St Jeor cross-check and the gap between them.
6. Use the tables. The activity table shows every multiplier at once so you can see the range, and the equation table shows how the three formulas compare on your own numbers.

Who this calculator is for

• Anyone told to use Harris-Benedict specifically by a coach, a nutrition course, a textbook or an older tracking app.
• Students and exam candidates in nutrition, nursing and exercise science, who need both the 1919 and 1984 coefficients and a worked example.
• People setting a first calorie target who want a defensible baseline rather than a guess.
• Anyone comparing formulas who wants to see the Harris-Benedict and Mifflin-St Jeor numbers side by side for the same body.
• Trainers and coaches who want a quick, consistent starting estimate for a client before adjusting from real-world results.

Key terms explained

• BMR (basal metabolic rate): calories burned at complete rest, measured fasted and lying still, to run your brain, heart, lungs, kidneys and basic cell function.
• RMR (resting metabolic rate): the same idea measured under slightly looser conditions. It usually comes out a little higher than BMR, and the terms are often used interchangeably in everyday planning.
• TDEE (total daily energy expenditure): BMR multiplied by your activity factor. This is the maintenance number you eat to hold your weight steady.
• Activity factor: the multiplier from 1.2 to 1.9 that scales BMR up for movement, exercise and the energy cost of digesting food.
• Calorie deficit or surplus: the gap between what you eat and your TDEE. About 500 calories a day corresponds to roughly a pound of weight change per week.
• Lean body mass: everything that is not fat, mostly muscle, organs, bone and water. It drives resting energy use, but a height-and-weight equation cannot see it.

What changes the result the most

• Activity level: by far the biggest lever. Moving one step up the scale changes the daily target by roughly 300 calories in the worked example.
• Body weight: each 20 lb adds about 121 calories for men and 84 for women in the revised equation.
• Sex: the male coefficients are larger across the board, so a man and a woman with identical height, weight and age are predicted several hundred calories apart.
• Age: a steady drain of about 57 calories per decade for men and 43 for women, which compounds over 30 or 40 years.
• Height: a smaller but real effect, about 12 calories per inch for men and 8 for women.
• Body composition: invisible to the equation, yet genuinely important. Two people at the same weight can differ by 200 calories or more if one carries far more muscle.

Tips for using your number well

• Treat it as a starting hypothesis. Eat at the predicted maintenance level for two to three weeks, weigh yourself consistently, and adjust by 100 to 200 calories based on the trend rather than a single weigh-in.
• Round down on activity. Most people over-rate how active they are. If you land between two levels, choose the lower one and let results argue you upward.
• Do not chase precision the equation cannot deliver. A 20-calorie difference between formula versions is noise next to normal day-to-day variation in intake and water weight.
• Keep protein and training in the plan. Preserving muscle in a deficit protects the resting metabolic rate this equation is trying to predict.
• Recalculate after real change. After losing or gaining 10 lb or more, run the numbers again. Your BMR moves with your body weight.

Limitations and assumptions

• The equation was built for healthy adults. It is not validated for children, and pregnancy and nursing add substantial needs it does not model.
• It uses total body weight, so it cannot distinguish muscle from fat and tends to over-predict at high body-fat percentages and under-predict in very lean, muscular people.
• It ignores medical and hormonal factors such as thyroid disorders, certain medications, fever and recovery from surgery or injury, all of which move resting energy use.
• The activity multipliers are coarse buckets, not measurements. Two people who both call themselves moderately active can differ by hundreds of calories.
• The 500 calories per pound per week rule is a simplification. Real weight change slows as you get lighter, because a smaller body burns less.
• The only exact measurement of resting energy use is indirect calorimetry in a clinical setting. Every formula on this page is an average.

How it compares to related calculators

This page answers "what does the Harris-Benedict equation say about me?" If your question is different, a sister tool fits better:

• For the modern Mifflin-St Jeor estimate of resting burn, use the BMR Calculator.
• To focus on activity multipliers and total daily burn, use the TDEE Calculator.
• To turn maintenance into a goal-based target, use the Calorie Calculator or the Maintenance Calories Calculator.
• To size a deficit and a timeline, use the Calorie Deficit Calculator or the Weight Loss Calculator.
• To split those calories into protein, carbs and fat, use the Macro Calculator or the Protein Calculator.
• For weight-for-height screening and body composition, use the BMI Calculator and the Body Fat Calculator.

Sources

• Roza AM, Shizgal HM (1984), "The Harris Benedict equation reevaluated: resting energy requirements and the body cell mass," American Journal of Clinical Nutrition - PubMed (National Library of Medicine, NIH).
• Mifflin MD, St Jeor ST, et al. (1990), "A new predictive equation for resting energy expenditure in healthy individuals," American Journal of Clinical Nutrition - PubMed (National Library of Medicine, NIH).
• Harris JA, Benedict FG (1919), A Biometric Study of Basal Metabolism in Man, Carnegie Institution of Washington - the original equation.
• National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK, NIH) - Weight Management.