BMR Formula Comparison 2026: Which Formula Is Most Accurate?

Mifflin-St Jeor is the most accurate BMR formula for most adults, predicting basal metabolic rate (BMR) within 10% of your true value. Harris-Benedict overestimates BMR by 5 to 15%, and Katch-McArdle only outperforms both formulas when you know your exact body fat percentage.

This BMR formula comparison walks you through all 3 equations, shows you real numbers from the same person, and tells you exactly which formula fits your situation in 2026.

Which BMR Formula Is Most Accurate?

Mifflin-St Jeor wins this BMR formula comparison for the general population. A 2005 review in the Journal of the American Dietetic Association tested 4 BMR equations against direct calorimetry and found Mifflin-St Jeor predicted resting energy expenditure more accurately than any competing formula.

The Mifflin-St Jeor equation matched measured BMR within 10% for most non-obese and obese adults tested. Harris-Benedict, published in 1919 and revised in 1984, overestimated BMR by 5 to 15% in the same study population.

Katch-McArdle changes this ranking only when you supply an accurate body fat percentage. Because Katch-McArdle calculates BMR from lean body mass instead of total weight, it produces a more precise number for athletes and for people carrying unusually high body fat.

Mifflin-St Jeor vs Harris-Benedict vs Katch-McArdle: The 3 Formulas Explained

Each formula in this BMR formula comparison uses a different set of inputs and a different data source. Below are the exact equations, the year each one was published, and the population each was built from.

Mifflin-St Jeor Formula (1990)

To calculate BMR with Mifflin-St Jeor, multiply your weight in kilograms (kg) and height in centimeters (cm) by fixed coefficients, then subtract an age adjustment.

• Men:   BMR = (10 x weight in kg) + (6.25 x height in cm) - (5 x age) + 5
• Women: BMR = (10 x weight in kg) + (6.25 x height in cm) - (5 x age) - 161

Researchers M.D. Mifflin and S.T. St Jeor built this formula from 498 healthy adults spanning a wide weight range, including obese participants. The formula replaced Harris-Benedict as the clinical standard in 1990 because it reflected modern body composition more closely than a 1919 sample.

Harris-Benedict Formula (Revised 1984)

To calculate BMR with the revised Harris-Benedict formula, apply larger constants and slightly different weight and height coefficients than Mifflin-St Jeor uses.

• Men:   BMR = 88.362 + (13.397 x weight in kg) + (4.799 x height in cm) - (5.677 x age)
• Women: BMR = 447.593 + (9.247 x weight in kg) + (3.098 x height in cm) - (4.330 x age)

James Harris and Francis Benedict developed the original equation at the Carnegie Institution in 1919. Their sample of 239 adults skewed young, lean, and mostly male. Researchers Roza and Shizgal recalibrated the coefficients in 1984, but the formula still overestimates BMR for older, heavier, and more sedentary adults.

Katch-McArdle Formula (1996)

To calculate BMR with Katch-McArdle, find your lean body mass (LBM) first, then plug that number into a single equation.

• BMR = 370 + (21.6 x LBM in kg)

LBM equals your total body weight multiplied by 1 minus your body fat fraction. A 175-lb (79-kg) man at 20% body fat carries an LBM of 63.2 kg. Exercise physiologists Victor Katch and Frank McArdle designed this formula to remove body fat from the calculation, since fat tissue burns far fewer calories than muscle at rest.

For the same 175-lb (79-kg) man at 10% body fat instead of 20%, LBM rises to 71.5 kg and BMR rises to 1,914 calories per day. That 159-calorie jump comes entirely from lower body fat, not from any change in scale weight.

Why Do BMR Formula Results Differ for the Same Person?

BMR formula results differ because each equation weighs weight, height, age, and lean mass differently. Mifflin-St Jeor and Harris-Benedict both use total body weight, so 2 people with identical height, weight, and age receive different BMR numbers purely from the coefficients each formula applies.

Harris-Benedict predicts a higher BMR than Mifflin-St Jeor in nearly every adult profile, and that gap widens for older, heavier, sedentary people. A sedentary 50-year-old man at 5 ft 10 in (178 cm) and 220 lb (100 kg) shows a 145-calorie gap between the two formulas.

Katch-McArdle breaks from both formulas by ignoring total weight entirely. Body composition, not scale weight, drives the Katch-McArdle number, so a lean athlete and a sedentary adult at the same weight receive very different results. Measurement error in body fat percentage also swings the Katch-McArdle output more than any error in Mifflin-St Jeor or Harris-Benedict.

Age adjustments compound this gap further. Harris-Benedict subtracts a smaller age penalty for men than Mifflin-St Jeor does, which is why the gap between the two formulas grows with every decade past 30. By age 60, that compounding effect alone can add up to 60 extra calories per day to the Harris-Benedict estimate.

Do Clinicians and Nutritionists Prefer One BMR Formula?

This part of the BMR formula comparison looks at clinical practice rather than lab theory. Clinicians increasingly favor Mifflin-St Jeor over Harris-Benedict for everyday nutrition planning.

One clinical comparison found Mifflin-St Jeor correct in 82% of non-obese patients and 70% of obese patients, compared with 69% and 64% for Harris-Benedict.

Hospital nutrition support teams still reference Harris-Benedict in some protocols, largely because of its long validation history in clinical settings. Newer treatment guidelines increasingly favor Mifflin-St Jeor or direct calorimetry when equipment allows.

Registered dietitians recommend Katch-McArdle only after confirming a client's body fat percentage through a professional method such as a DEXA scan or skinfold calipers. Without that confirmation, dietitians default to Mifflin-St Jeor for the same reason home users should: consistent, low-error inputs beat a theoretically sharper formula fed with guessed numbers.

How to Choose the Right BMR Formula for Your Body

To finish this BMR formula comparison for your own body, start by asking whether you know your body fat percentage. That single answer determines which of the 3 equations gives you the most reliable number.

How to Choose a BMR Formula Without Body Fat Data

To choose a BMR formula without body fat data, default to Mifflin-St Jeor. Mifflin-St Jeor needs only 4 inputs, sex, age, height, and weight, all of which you can measure with a scale and a tape measure.

Use Harris-Benedict as a cross-check, not a primary source. If Mifflin-St Jeor and Harris-Benedict land within 50 calories of each other, treat that range as well-anchored. Our body fat percentage calculator gives you a fast estimate using the Navy tape method if you decide you need Katch-McArdle later.

How to Choose a BMR Formula With Body Fat Data

To choose a BMR formula with body fat data, switch to Katch-McArdle whenever your body fat percentage comes from a repeatable method. Reliable methods include DEXA scans, skinfold calipers, and consistent bioelectrical impedance analysis (BIA) readings taken at the same time of day.

Choose Katch-McArdle if you fall into 1 of 2 groups: athletes with low body fat, or adults with high body fat where Mifflin-St Jeor tends to overestimate BMR. Skip Katch-McArdle if your body fat percentage is a rough guess, since an inaccurate LBM input produces a less reliable BMR than Mifflin-St Jeor's simpler inputs.

Same Person, 3 Formulas: A Worked Example

To see how much these formulas actually diverge, take 1 example: a 35-year-old woman at 5 ft 5 in (165 cm) and 150 lb (68 kg), sedentary, with a measured body fat percentage of 28%.

Mifflin-St Jeor puts her BMR at 1,395 calories per day. Harris-Benedict puts the same woman at 1,485 calories per day, a 90-calorie overestimate. Katch-McArdle, using her measured lean body mass of 48.9 kg, calculates 1,426 calories per day, splitting the difference between the other 2 formulas.

The 90-calorie gap between Mifflin-St Jeor and Harris-Benedict looks small on paper. Over 8 weeks at a 20% cutting deficit, that gap can shift total fat loss by roughly 1.5 lb (0.7 kg), enough to stall progress if your calorie target sits on the wrong baseline.

Use this quick-reference table to finish your BMR formula comparison in seconds.

Your BMR formula choice also changes your metabolic age result. Metabolic age compares your BMR against age-group averages, so a formula that overestimates BMR by 90 calories can make your metabolic age look several years younger than it actually is. Run your inputs through Mifflin-St Jeor first, since most age-group average tables are built from that formula, then treat Harris-Benedict or Katch-McArdle results as secondary reference points.

BMR vs RMR: What Is the Real Difference?

BMR and resting metabolic rate (RMR) are not identical, though the terms get used interchangeably online. BMR measures energy expenditure under strict laboratory conditions: fasted for 12 hours, fully rested, and in a thermoneutral room.

RMR measures energy expenditure under looser resting conditions and typically comes out 5 to 10% higher than true BMR. Every formula in this BMR formula comparison, Mifflin-St Jeor, Harris-Benedict, and Katch-McArdle, technically predicts RMR rather than lab-measured BMR, since none of them require a fasting or thermoneutral protocol.

The distinction matters less for daily planning than the number itself. Whether you call your result BMR or RMR, treat it as a starting baseline, then adjust based on your metabolic age results and real-world weight trends over several weeks.

How to Use Your BMR Number for Weight Loss or Muscle Gain

To use your BMR number for weight loss, multiply it by an activity factor to reach your total daily energy expenditure (TDEE), then subtract 15 to 20% for a sustainable deficit. Activity factors range from 1.2 for a sedentary lifestyle to 1.9 for very intense daily training. Choosing a factor 1 level too high is the most common reason a calorie target stalls fat loss, regardless of which BMR formula supplied the starting number.

To use your BMR number for muscle gain, multiply BMR by your activity factor, then add 10 to 15% to create a lean surplus. Pair that surplus with resistance training at least 3 times per week, or the extra calories convert to fat rather than muscle.

Split your calorie target into protein, carbohydrate, and fat grams using a daily macro calculator once you settle on a number. Aim for 1.6 to 2.2 grams (g) of protein per kilogram (kg) of body weight regardless of your goal, since protein preserves muscle during a deficit and supports repair during a surplus.

Recalculate your BMR every 10 to 15 lb (4.5 to 6.8 kg) of weight change. BMR drops as body weight drops, so a target set 3 months ago no longer reflects your current calorie needs.

Common Mistakes When Comparing BMR Formulas

4 mistakes account for most of the confusion in BMR formula comparisons.

1. Using Katch-McArdle with a guessed body fat percentage creates the biggest error. A body fat guess that is off by 5 percentage points shifts your BMR estimate by more than 100 calories, which defeats the formula's main advantage.
2. Treating any single formula as a lab measurement causes a second common error. Mifflin-St Jeor, Harris-Benedict, and Katch-McArdle all produce estimates, not measurements. Indirect calorimetry remains the only direct measurement method available outside a hospital setting.
3. Ignoring body composition changes over time causes the third error. Muscle gain or fat loss changes your true BMR within 8 to 12 weeks, so recalculating on a fixed schedule keeps your numbers accurate.
4. Mixing measurement units causes the fourth error. Combining pounds with centimeters, or feet with kilograms, inside 1 formula produces a BMR number that is off by hundreds of calories. Convert weight to kilograms (kg) and height to centimeters (cm) before running any of the 3 equations.

The research behind this BMR formula comparison traces back to 3 original publications: Mifflin MD et al. (1990), Roza and Shizgal (1984), and the reference texts of Katch and McArdle. Frankenfield et al. (2005) later validated all 3 equations against direct calorimetry.

Frequently Asked Questions

Is Katch-McArdle more accurate than Mifflin-St Jeor?

Yes, Katch-McArdle can be more accurate than Mifflin-St Jeor, but only when your body fat percentage comes from a reliable, repeatable method such as a DEXA scan. A guessed body fat number erases that advantage immediately.

Is Harris-Benedict outdated?

Yes, Harris-Benedict is considered less accurate than Mifflin-St Jeor for modern populations, since the original 1919 sample skewed lean and young. It still works as a cross-check, not a primary source.

Which BMR formula should I use if I lift weights?

Katch-McArdle often wins this BMR formula comparison for lifters, since it calculates BMR from lean body mass rather than total scale weight. Confirm your body fat percentage with calipers or a DEXA scan before trusting the result.

Do BMR formulas measure my actual metabolism?

No, BMR formulas estimate resting energy expenditure from limited inputs like weight, height, age, and sex. Indirect calorimetry remains the only direct measurement method.

How often should I recalculate my BMR?

Recalculate your BMR every 10 to 15 lb (4.5 to 6.8 kg) of weight change, or every 90 days if your weight stays stable. Muscle and fat shifts change your true number even when the scale does not move.

Mifflin-St Jeor gives you the most reliable BMR formula comparison result if you are starting without body fat data. Katch-McArdle takes over the moment you have a trustworthy body fat percentage in hand. Set your first target with our calorie deficit calculator, then adjust it using 2 to 4 weeks of real weight trends.