๐งฎ Harris-Benedict BMR Calculator
The 1984 revised equation, with TDEE at five activity levels.
Estimates for planning only, not medical advice.
The Harris-Benedict equation is the grandparent of every calorie calculator on the internet, first published in 1919 and revised in 1984 by Roza and Shizgal. This calculator uses the 1984 revision: plug in sex, age, height, and weight, and it estimates your basal metabolic rate, the calories you burn doing absolutely nothing. It also shows your TDEE at five activity levels and, for honesty, the Mifflin-St Jeor number alongside so you can see the gap.
How to Use This Calculator
Enter your sex, age, height in centimeters, and weight in kilograms, then pick the activity level that matches your real life, not your aspirational one.
Enter your stats. Morning weight, height without shoes, age in whole years.
Choose activity honestly. A desk job with three gym sessions is lightly active, not very active. Most people overestimate by one full level.
Read your BMR, then the TDEE rows. The TDEE at your activity level is the maintenance calorie number to plan around.
Compare with the Mifflin-St Jeor row. Harris-Benedict usually reads a few percent higher. For the full Mifflin-based planner, see our BMR calculator and TDEE calculator.
The 1984 Revised Equations
Harris and Benedict derived the original 1919 equations from calorimetry measurements on 239 subjects. The 1984 revision by Roza and Shizgal refit the constants against a larger, more modern dataset, which is the version every calculator worth using runs today. Each term has a physical meaning: weight drives most of the burn because tissue costs energy to maintain, height adds a smaller frame-size correction, and age subtracts a bit each year as metabolism slows. The sex difference reflects average body composition, since muscle burns more at rest than fat does.
The activity multipliers come from the same tradition: 1.2 for sedentary, 1.375 light, 1.55 moderate, 1.725 very active, 1.9 for athletes and heavy labor. They are rough, and the honest error band on any BMR equation is about plus or minus 10 percent. Treat the output as a starting estimate to test against the scale over two to three weeks, not as a lab measurement.
Worked Example
A 35-year-old man, 177.8 cm (5 foot 10), 81.6 kg (180 lb). BMR = 88.362 + 13.397 x 81.6 + 4.799 x 177.8 - 5.677 x 35 = 88.362 + 1093.2 + 853.3 - 198.7 = 1,836 kcal/day. Mifflin-St Jeor for the same man: 10 x 81.6 + 6.25 x 177.8 - 5 x 35 + 5 = 1,757 kcal/day. Harris-Benedict reads 79 kcal higher, about 4.5 percent, which matches the literature: the 2005 review in the Journal of the American Dietetic Association found Harris-Benedict overestimates by roughly 5 percent versus Mifflin-St Jeor in most adults. Lightly active TDEE: 1,836 x 1.375 = 2,525 kcal/day.
Harris-Benedict vs Mifflin-St Jeor: Which to Use
For most adults, Mifflin-St Jeor. The Academy of Nutrition and Dietetics recommends it because validation studies show it lands within 10 percent of measured resting burn for more people. Harris-Benedict remains useful in two situations: clinical settings with older protocols built around it, and anyone who wants to see both numbers before committing to a calorie target. The practical move is to average the two when they disagree, then adjust based on what the scale does over two weeks. If they agree within 100 kcal, you have a solid number.
Neither equation knows your body composition. Very muscular people burn more than predicted and very high body-fat percentages burn less per pound, because muscle is metabolically expensive and fat is cheap. If you know your body fat percentage, the Katch-McArdle equation uses lean mass directly and beats both of these at the extremes. And if you are eating at the number and the scale is not moving after three honest weeks, the number is wrong, not your body: drop it by 10 percent and retest.
From BMR to a Real Plan
BMR is the floor, not the target. Nobody eats at BMR unless bedridden: your TDEE row is the maintenance number. To lose fat, eat 300 to 500 kcal under TDEE; to gain muscle, eat 200 to 300 over. Protein anchors everything at 0.7 to 1 gram per pound of body weight, and our macro calculator splits the rest into carbs and fat. Recalculate every 10 to 15 pounds of change, because a lighter body burns less and the old target quietly becomes a surplus.
For informational purposes only, not medical advice. Consult a healthcare professional.
Frequently Asked Questions
What is the Harris-Benedict equation?
A BMR formula first published in 1919 by J. Arthur Harris and Francis Benedict, revised in 1984 by Roza and Shizgal with updated constants. The revised version for men is 88.362 + 13.397 x weight(kg) + 4.799 x height(cm) - 5.677 x age, and for women 447.593 + 9.247 x weight(kg) + 3.098 x height(cm) - 4.330 x age.
Is Harris-Benedict or Mifflin-St Jeor more accurate?
Mifflin-St Jeor, for most adults. A well-known 2005 review found it predicts resting burn within 10 percent for more people, while Harris-Benedict overestimates by about 5 percent on average. The Academy of Nutrition and Dietetics recommends Mifflin-St Jeor for healthy adults. This calculator shows both so you can compare.
What is the difference between the original and revised Harris-Benedict?
The 1919 original was fitted to 239 early-1900s subjects. The 1984 revision refit the constants to a larger modern dataset. The revised constants are the ones every current calculator uses; if a site does not say which version it runs, assume revised, but the honest ones say so.
How do I convert BMR to TDEE?
Multiply by an activity factor: 1.2 sedentary, 1.375 lightly active, 1.55 moderately active, 1.725 very active, 1.9 extra active. The result is your estimated total daily energy expenditure, the maintenance calorie number. This calculator shows all five levels.
Why does Harris-Benedict give a higher number than Mifflin?
Its constants were fitted to a different, older population sample and it tends to overestimate resting burn by roughly 5 percent in modern adults. The gap is systematic, not random, which is why comparing the two is informative rather than confusing.
Does Harris-Benedict work for obese individuals?
Less well. Like all weight-based equations, it overestimates for very high body fat percentages because fat is metabolically cheaper than the formula assumes. For obesity, clinicians often use adjusted body weight or the Mifflin-St Jeor equation, and for the very muscular or very lean, Katch-McArdle.
What activity level should I choose?
Be honest and pick one level lower than your instinct. A desk job plus three workouts a week is lightly active. Five hard sessions plus an active job is very active. Almost no recreational exerciser is extra active; that factor is for athletes and manual laborers.
How accurate is my BMR result?
Expect plus or minus 10 percent versus a lab measurement. Equations estimate from population averages; your thyroid, muscle mass, and even room temperature shift the real number. Use the result as a starting estimate and adjust based on two to three weeks of scale data.
Should athletes use Harris-Benedict?
They can, but Katch-McArdle is better for athletes because it uses lean body mass directly instead of inferring composition from weight. A 220-pound lifter and a 220-pound sedentary person get very different Harris-Benedict numbers only through the same weight term, which misses the point.
How often should I recalculate my BMR?
Every 10 to 15 pounds of weight change, and yearly as you age. A lighter body burns less, so an old target quietly becomes a surplus. If the scale stalls for three honest weeks at your calculated target, the target is wrong: adjust by 10 percent and retest.