BMR Calculator

Your basal metabolic rate is the energy your body burns at complete rest, before you get out of bed or eat anything. This calculator uses Mifflin-St Jeor, the equation the Academy of Nutrition and Dietetics recommends, and puts Harris-Benedict and Katch-McArdle beside it so you can see how far apart the estimates land. BMR is also the base component of your TDEE: multiply it by an activity factor and you get what you actually burn across a full day.

BMR Details

Mifflin-St Jeor by default, with Harris-Benedict and Katch-McArdle alongside it

Sex

Age

Weight (lb)

Height (ft)

Height (in)

Body fat % (optional)

Only needed for the Katch-McArdle result. Leave blank if you don't know it.

Your BMR will appear here

Enter your details, then click calculate to see your BMR across three formulas.

CalcClearly Health & Fitness Team

Formula selection based on the Academy of Nutrition and Dietetics recommendation

This page is researched and maintained by CalcClearly's editorial team. The default equation used here is the one the Academy of Nutrition and Dietetics rates 'Strong' for adults, and every claim on this page is checked against the published research behind it. It's general education, not a substitute for advice from a doctor or registered dietitian.

BMR vs TDEE: Which Number To Eat

BMR is the base component of TDEE, so the two numbers are related but they answer different questions. BMR tells you what your body costs to keep running if you never moved. TDEE tells you what a real day costs, walking to the car and standing in the kitchen and training included.

TDEE = BMR × activity factor

Sedentary: ×1.2, desk job with little or no exercise
Lightly active: ×1.375, exercise 1 to 3 days a week
Moderately active: ×1.55, exercise 3 to 5 days a week
Very active: ×1.725, exercise 6 to 7 days a week
Extremely active: ×1.9, hard daily training or a physical job

The 35-year-old woman in the example below has a BMR of 1,345 calories. If she trains a couple of times a week, her TDEE is 1,345 × 1.375, about 1,850 calories a day. That gap of roughly 500 calories is the reason eating at your BMR feels so punishing: it ignores every calorie you spend actually living.

If you want calorie and macro targets rather than a resting baseline, run the numbers through the TDEE Calculator, which takes your activity level and your goal into account.

Why This Calculator Defaults To Mifflin-St Jeor

There are dozens of BMR equations in circulation, and plenty of calculators quietly pick one without saying which. This one leads with Mifflin-St Jeor (1990) because the Academy of Nutrition and Dietetics, the professional body for registered dietitians in the United States, recommends it for adults with a rating of "Strong", their highest evidence grade.

That recommendation rests on a systematic review by Frankenfield, Roth-Yousey and Compher, published in the Journal of the American Dietetic Association in 2005. The review compared the four equations most used in clinical practice, Harris-Benedict, Mifflin-St Jeor, Owen, and the WHO/FAO/UNU equations, against measured resting metabolic rate. Mifflin-St Jeor came out the most reliable of the group, predicting RMR within 10% of the measured value in more people, both nonobese and obese, than any other equation, and with the smallest margin of error.

Harris-Benedict is still shown here because it remains common in older tools, and Katch-McArdle earns its place for anyone who knows their body fat percentage, since it works from lean mass instead of total weight. Seeing all three at once makes the uncertainty visible rather than hiding it behind one confident-looking number.

Source: 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.

Quick Answer

BMR is the number of calories your body burns at complete rest. The Mifflin-St Jeor equation calculates it as (10 × weight in kg) + (6.25 × height in cm) − (5 × age), then adds 5 for men or subtracts 161 for women. It is a minimum, not an eating target: multiply it by an activity factor to get your TDEE, which is the number to plan meals around.

How It Works: Formula & Variables

W is weight in kilograms, H is height in centimeters, A is age in years, and every result is calories per day. All three equations were calibrated in metric, so imperial entries are converted to kg and cm before anything is calculated.

Mifflin-St Jeor, men = (10 × W) + (6.25 × H) − (5 × A) + 5

Mifflin-St Jeor, women = (10 × W) + (6.25 × H) − (5 × A) − 161

Harris-Benedict, men = 88.362 + (13.397 × W) + (4.799 × H) − (5.677 × A)

Harris-Benedict, women = 447.593 + (9.247 × W) + (3.098 × H) − (4.330 × A)

Katch-McArdle = 370 + (21.6 × LBM)

LBM = W × (1 − body fat percentage as a fraction)

Mifflin-St Jeor (1990): The default here, and the equation the Academy of Nutrition and Dietetics recommends for adults.
Harris-Benedict (1984): The revised version of the 1919 original. Still widely used, though it tends to read slightly high.
Katch-McArdle: Sex-neutral and driven by lean body mass, so it needs a body fat percentage to work.

Worked Examples

Example 1: Woman, 35 years, 65 kg, 165 cm

Mifflin-St Jeor: BMR = (10 × 65) + (6.25 × 165) − (5 × 35) − 161 = 650 + 1,031.25 − 175 − 161 = 1,345.25, so about 1,345 calories/day.

On the same inputs, Harris-Benedict revised gives roughly 1,408 calories/day, and Katch-McArdle at 30% body fat (lean mass 45.5 kg) gives about 1,353 calories/day. Three respected equations, three different answers, spread across about 60 calories. That spread is small next to the roughly ±10% each one carries against a real metabolic test, which is worth keeping in mind before treating any single figure as exact.

Example 2: Man, 40 years, 185 lb, 5'11"

Converted first: 185 lb is 83.9 kg, and 5'11" is 180.3 cm. Mifflin-St Jeor: BMR = (10 × 83.9) + (6.25 × 180.3) − (5 × 40) + 5 = 839 + 1,126.9 − 200 + 5, or about 1,771 calories/day. Harris-Benedict revised comes to roughly 1,851, and Katch-McArdle at 18% body fat (lean mass 68.8 kg) lands near 1,856.

At a moderate activity level his TDEE would be 1,771 × 1.55, close to 2,745 calories/day, which is nearly a thousand calories above his resting baseline.

Key Concepts

BMR is a minimum, not a target: it represents the calories burned by a body at total standstill. Eating at that level long term means underfeeding everything you do on top of lying still.

Lean mass does most of the work: muscle burns more energy at rest than fat does, which is why the equations split by sex and why Katch-McArdle skips sex entirely once it knows your lean body mass.

These formulas predict RMR: the numbers you see are technically resting metabolic rate, measured under looser conditions than true BMR. The industry labels them BMR anyway, so this page follows that convention.

Age pulls the number down: every equation subtracts calories per year of age, since resting metabolism tends to drop as muscle mass declines over time.

Common Mistakes

Eating at your BMR: the most common and most damaging mistake. BMR is an absolute floor, the calories burned at complete standstill, and it was never meant as a diet goal. The right reference point for what to eat is your TDEE, adjusted for whether you want to lose, maintain, or gain.

Confusing BMR with TDEE: people who read their BMR as a daily allowance often end up eating hundreds of calories below what they need, then wonder why energy, training, and mood all fall apart.

Confusing BMR with RMR: the two are measured under different protocols and RMR usually sits a little higher. Comparing a BMR estimate from one tool to an RMR reading from another will show a gap that has nothing to do with your metabolism changing.

Entering the wrong units: typing pounds where the formula expects kilograms, or inches where it expects centimeters, produces a number that looks plausible and is badly wrong. Pick a unit system at the top and stay in it.

Treating the estimate as exact: an equation using four inputs cannot know your thyroid function, your training history, or how much muscle you carry. Expect ±10%, and adjust based on what actually happens to your weight over a few weeks.

Frequently Asked Questions

BMR is what your body burns doing nothing at all, just keeping your heart, lungs, brain, and organs running. TDEE is that same number scaled up for everything else you do: TDEE = BMR × activity factor. The standard factors are 1.2 for sedentary, 1.375 for lightly active, 1.55 for moderately active, 1.725 for very active, and 1.9 for extremely active. Take a 35-year-old woman at 65 kg and 165 cm, whose BMR works out to about 1,345 calories a day. If she trains a couple of times a week, her TDEE is 1,345 × 1.375, which is roughly 1,850 calories. BMR is the floor. TDEE is the number you plan your eating around.

The two sit very close together and get used interchangeably all the time, but they are measured under different conditions. A true BMR reading is taken in a darkened room, lying down, after eight hours of sleep and twelve hours of fasting, which is about as strict a baseline as testing gets. RMR is measured under looser conditions, usually after an overnight fast without the full protocol. Since those conditions are more relaxed, RMR normally comes out a bit higher than genuine BMR. In practice, the Mifflin-St Jeor equation predicts RMR, and consumer tools like this one call that same number BMR.

For most people, Mifflin-St Jeor. It is the equation the Academy of Nutrition and Dietetics recommends, and it is the most validated one for the general population, which is why this calculator shows it first. If you know your body fat percentage and you are lean or athletic, run the Katch-McArdle result as a second check, since it works from lean body mass rather than total weight. Harris-Benedict is included mainly for comparison, because a lot of older tools and fitness apps still use it.

Even the best equation lands within roughly 10% of your real resting metabolism for about 80% of people, and it can miss by more than that if your body composition sits at either extreme. Someone carrying a lot of muscle or a lot of fat is exactly the case where a height-and-weight formula struggles. Treat the number as a starting estimate rather than a measurement. The only way to know your actual figure is indirect calorimetry, done in a clinic or a sports lab.

At the same height, weight, and age, men on average carry more muscle and less fat than women, and muscle tissue burns more energy at rest than fat tissue does. The Mifflin-St Jeor equation handles that difference with a single constant at the end: it adds 5 for men and subtracts 161 for women. Everything before that constant is identical. The Katch-McArdle equation skips the split entirely, since it already works from your lean mass.

Your current weight, your height, your age, and your sex. That covers Mifflin-St Jeor and Harris-Benedict. Add your body fat percentage if you know it and the Katch-McArdle result appears as well. Enter your details in whichever unit system you think in, imperial or metric, and the calculator converts to kilograms and centimeters behind the scenes, since that is what all three equations are built for.

Last reviewed 2026-07-23. For educational purposes only — not professional advice.