BMR Calculator

How to use this calculator

Choose US or metric units, then enter your sex, age, height and weight. The calculator shows your BMR from the Mifflin-St Jeor equation by default. Under Formula & body fat you can switch to the revised Harris-Benedict equation or, if you enter your body fat percentage, Katch-McArdle. You’ll see:

• your BMR in calories per day, and per hour
• a formula comparison table with each equation filled in with your numbers
• what your BMR means for maintenance calories at sedentary and moderate activity
• the full working for every formula

BMR is the floor of your calorie burn, not a target. To see what you burn on an average day including activity, use the TDEE calculator.

The BMR formulas

All three equations take weight (W) in kilograms, height (H) in centimeters and age (A) in years. The calculator converts US units for you: 1 inch = 2.54 cm and 1 kg = 2.2046 lb.

Mifflin-St Jeor (1990). Developed from measurements of 498 healthy adults, including people of normal weight and with obesity.

Harris-Benedict, revised by Roza and Shizgal (1984). The original Harris-Benedict equations date from 1918–1919. Roza and Shizgal recalculated the coefficients using the original data plus additional subjects Benedict published later.

Katch-McArdle. Uses lean body mass (LBM) instead of total weight, so it ignores sex and age:

Worked example

A 35-year-old woman who is 5 ft 5 in and 160 lb, with 30% body fat:

1. Convert: 65 in × 2.54 = 165.1 cm; 160 lb ÷ 2.2046 = 72.6 kg
2. Mifflin-St Jeor: 10 × 72.6 + 6.25 × 165.1 − 5 × 35 − 161 = 1,422 calories
3. Revised Harris-Benedict: 447.593 + 9.247 × 72.6 + 3.098 × 165.1 − 4.330 × 35 = 1,479 calories
4. Lean body mass: 72.6 × (1 − 0.30) = 50.8 kg; Katch-McArdle: 370 + 21.6 × 50.8 = 1,467 calories

The three estimates fall within 57 calories of each other, about 4%. Her BMR works out to roughly 59 calories an hour. If she were sedentary, her maintenance calories would be about 1,422 × 1.2 = 1,706 a day.

The formulas don’t always agree this closely. For a 40-year-old man who is 5 ft 10 in and 190 lb with 25% body fat, Mifflin-St Jeor gives 1,778, revised Harris-Benedict 1,869 and Katch-McArdle 1,766. In both examples, Harris-Benedict comes out higher than Mifflin-St Jeor.

BMR by weight

Mifflin-St Jeor estimates for 40-year-olds: women at 5 ft 4 in and men at 5 ft 10 in.

Each extra 20 lb adds about 91 calories a day. Each extra year of age subtracts 5, so the same man would have a BMR about 50 calories lower at 50 than at 40.

What affects your BMR

• Body size. Larger bodies have more tissue to maintain.
• Muscle mass. Lean tissue burns more energy at rest than fat tissue, which is why Katch-McArdle uses lean mass directly.
• Age. BMR tends to fall through adulthood, partly because muscle mass declines.
• Sex. At the same height and weight, men usually have more lean mass, so the equations give them a higher BMR.
• Other factors the equations can’t see: genetics, thyroid function, some medications, illness and recent dieting.

Using your BMR

Your BMR is the starting point for any calorie plan, but not a number to eat at. Multiply it by an activity factor to get your maintenance calories, as the TDEE calculator does, then adjust up or down for your goal with the calorie calculator. If you’re working toward a specific weight by a specific date, the calorie deficit calculator does the whole plan in one step.

Assumptions and limitations

• These equations predict averages. In a 2005 systematic review, Mifflin-St Jeor came within 10% of measured resting metabolism more often than the others, but some individuals were further off with every equation.
• Katch-McArdle is only as good as your body fat measurement. Bathroom-scale estimates can be off by several percentage points.
• The equations were developed in adults and don’t apply to children, teens, or pregnant or breastfeeding people.
• A lab test (indirect calorimetry) is the only way to measure your metabolic rate directly.

Sources

• Mifflin MD, St Jeor ST, Hill LA, et al. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 1990;51(2):241–247.
• Roza AM, Shizgal HM. The Harris Benedict equation reevaluated: resting energy requirements and the body cell mass. Am J Clin Nutr. 1984;40(1):168–182.
• McArdle WD, Katch FI, Katch VL. Exercise Physiology: Nutrition, Energy, and Human Performance. Wolters Kluwer (source of the Katch-McArdle equation).
• Frankenfield D, Roth-Yousey L, Compher C. Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review. J Am Diet Assoc. 2005;105(5):775–789.

These are estimates for healthy adults and aren’t medical advice. If you’re concerned about your metabolism, talk to your doctor.

Updated November 2026. Results are estimates for educational purposes and depend on the inputs you provide.