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BMR formula: the three equations, and how BMR differs from RMR and TDEE
The most widely used BMR formula is Mifflin-St Jeor: 10 × weight (kg) + 6.25 × height (cm) − 5 × age, then + 5 for men or − 161 for women. Two other formulas are common, Harris-Benedict and Katch-McArdle. All three give estimates, and they can differ by close to 100 calories for the same person.
These are example numbers. Enter your own above.
Your maintenance calories, as a range across equations
Each equation's BMR × 1.2 for your activity level. Mean of the equations 2,157 kcal/day, and the equations disagree by 90 kcal.
Your activity choice moves this estimate more than the equations disagree. One step to “Lightly active” moves the mean about 314 kcal/day, while the equations on your row span 90 kcal/day.
Is exercise already included? Yes. The “Sedentary” multiplier (×1.2) already covers your workouts and daily movement. Do not add calories burned in the gym on top of this number. Double-counting exercise is the most common reason these estimates come out too high.
| Mifflin-St Jeor | 2,112 kcal |
|---|---|
| Revised Harris-Benedict | 2,202 kcal |
| Katch-McArdle | add body fat % to include it |
| Activity level | Factor | Maintenance |
|---|---|---|
| Sedentaryselected | ×1.2 | 2,112–2,202 kcal |
| Lightly active | ×1.375 | 2,420–2,523 kcal |
| Moderately active | ×1.55 | 2,728–2,844 kcal |
| Very active | ×1.725 | 3,036–3,165 kcal |
| Extra active | ×1.9 | 3,344–3,486 kcal |
Show the work
Each equation estimates your basal metabolic rate (BMR), the energy you use at complete rest, from your sex, age, height and weight. Katch-McArdle instead uses lean body mass, which is why it needs a body fat percentage. Every BMR is then multiplied by your activity factor (×1.2) to reach maintenance calories. The range you see is the spread between equations, not a margin of error for your body.
Your weight, height, age, sex and body fat stay in this browser, on this device. Nothing is uploaded, there is no account, and no other company receives any of it. The button below deletes what this page stored, where this browser allows it.
Supported inputs: ages 18–80; height 130–230 cm (4 ft 3 in – 7 ft 7 in); weight 35–250 kg (77–551 lb); body fat 8–55% or blank. Imperial figures are rounded; metric limits are exact. Results are shown in whole calories per day.
The BMR formula: three equations
Three equations commonly appear in BMR calculators. Mifflin-St Jeor uses weight, height, age and sex. Revised Harris-Benedict uses the same inputs with different coefficients. Katch-McArdle uses lean body mass instead of total body weight. All three are predictive equations: they estimate energy use from body measurements rather than measuring it.
| Formula | Men | Women | Needs body fat? |
|---|---|---|---|
| Mifflin-St Jeor (1990) | 10W + 6.25H − 5A + 5 | 10W + 6.25H − 5A − 161 | No |
| Harris-Benedict, revised (1984) | 88.362 + 13.397W + 4.799H − 5.677A | 447.593 + 9.247W + 3.098H − 4.330A | No |
| Katch-McArdle | 370 + 21.6 × LBM | same | Yes |
W = kg, H = cm, A = years, LBM = lean body mass in kg = weight × (1 − body fat % ÷ 100).
Mifflin-St Jeor BMR formula
The Mifflin-St Jeor equation was published in 1990 as a predictive equation for resting energy expenditure (Mifflin and colleagues, 1990). The Academy of Nutrition and Dietetics names it for overweight and obese adults when resting metabolic rate cannot be measured (Academy of Nutrition and Dietetics).
Harris-Benedict BMR formula
An original 1919 version exists (Harris and Benedict, 1919). The 1984 revision shown here is the one this calculator runs (Roza and Shizgal, 1984).
Katch-McArdle BMR formula
The Katch-McArdle equation works from lean body mass, the strongest single predictor in the 1990 study (Mifflin and colleagues, 1990). It is presented in McArdle, Katch and Katch, Exercise Physiology, and its result is only as good as the body fat figure entered.
How to calculate your basal metabolic rate
Calculating basal metabolic rate has three steps.
First, convert the inputs to the units the equation expects. Weight is in kilograms, height is in centimetres, and age is in years.
Second, pick one formula. Do not combine coefficients from different equations.
Third, apply the arithmetic and round the result as appropriate.
The maintenance calorie calculator applies the inputs for you. The worked example below shows why two calculators can produce different answers even when the same body measurements are entered.
The example is a man aged 30, 5 ft 10 in, 175 lb (79.38 kg, 177.8 cm), 20% body fat.
| Formula | Working | BMR |
|---|---|---|
| Mifflin-St Jeor | 793.8 + 1,111.25 − 150 + 5 | 1,760 |
| Revised Harris-Benedict | 88.362 + 1,063.4 + 853.3 − 170.3 | 1,835 |
| Katch-McArdle | 370 + 21.6 × 63.5 | 1,742 |
The widest gap in this example is 93 kcal, between 1,835 and 1,742. The formulas are estimates, so the equation selected changes the output.
The BMR formula in pounds and inches
The Mifflin-St Jeor equation can be written in pounds and inches as:
4.536 × lb + 15.875 × in − 5 × age + 5 for men
or:
4.536 × lb + 15.875 × in − 5 × age − 161 for women
This is the same equation with the unit conversions folded in. For the worked man, the result is 1,760.
TDEE vs BMR: what is the difference?
BMR is the resting estimate. TDEE is BMR multiplied by an activity factor from 1.2 to 1.9, so it represents a full-day estimate rather than the resting figure alone. The factor changes the arithmetic, which is why the same BMR can produce several TDEE values.
| What it estimates | Conditions | Relationship | |
|---|---|---|---|
| BMR | Energy at complete rest | Base figure | |
| RMR / REE | Energy at rest | What the formulas actually predict (Mifflin and colleagues, 1990; Roza and Shizgal, 1984) | |
| TDEE | Energy across a full day | Includes all movement | BMR or RMR × activity factor |
If my BMR is 1,500, what is my TDEE?
| Factor | Level | TDEE |
|---|---|---|
| 1.2 | Sedentary | 1,800 |
| 1.375 | Lightly active | 2,063 |
| 1.55 | Moderately active | 2,325 |
| 1.725 | Very active | 2,588 |
| 1.9 | Extra active | 2,850 |
These factors are a convention, not a validated output. The table shows the arithmetic of the calculator model, not a measured daily total.
Should I eat my BMR or my TDEE?
TDEE, not BMR, is the estimate of the energy that holds weight steady. BMR leaves out every step you take. This page does not set intake targets.
BMR vs RMR: what is the difference?
BMR means basal metabolic rate. RMR means resting metabolic rate, and REE means resting energy expenditure. Many calculators use the terms interchangeably. That label does not change the arithmetic inside the equation. It does mean that the result should be treated as a predicted resting value rather than a direct measurement.
Are BMR formulas really RMR formulas?
All three equations this site runs were fitted to resting energy expenditure, not basal energy expenditure. The 1990 Mifflin paper is titled "a new predictive equation for resting energy expenditure" (Mifflin and colleagues, 1990). The 1984 Roza and Shizgal paper uses the phrase "resting energy requirements" (Roza and Shizgal, 1984). The 2023 revision is titled "New Human Resting Metabolic Rate Equation" (Pavlidou and colleagues, 2023).
Calculators, including this one, call the result BMR by convention.
What does BMR stand for?
BMR stands for basal metabolic rate. It is an estimate of the energy the body uses at complete rest under basal conditions. The formulas above calculate that estimate from measured weight, height, age, sex and, for Katch-McArdle, lean body mass.
What is basal metabolic rate?
Basal metabolic rate is an estimate of the energy the body uses at complete rest. It is a resting figure, not a full-day total, because it does not include movement across the day. A BMR calculator uses a predictive equation rather than a direct measurement. The three equations above can give different results for the same body, as the 1,742 to 1,835 spread in the worked example shows.
What is a normal BMR?
There is no single normal BMR figure. The arithmetic changes with body size, age and sex, so a lower result can reflect a smaller or older body in the equation. A BMR is an estimate, not a diagnosis. The table below runs the Mifflin-St Jeor equation for six different bodies. A woman aged 75 who weighs 105 lb and stands 5 ft 0 in has a BMR of 893. A woman aged 25 who weighs 120 lb and stands 5 ft 3 in has a BMR of 1,258. The difference comes from age, height and weight in the arithmetic, not from a health rating.
| Body | BMR |
|---|---|
| Woman, 75, 5 ft 0 in, 105 lb | 893 |
| Woman, 25, 5 ft 3 in, 120 lb | 1,258 |
| Woman, 50, 5 ft 6 in, 160 lb | 1,362 |
| Man, 25, 5 ft 9 in, 160 lb | 1,701 |
| Man, 60, 6 ft 0 in, 200 lb | 1,755 |
| Man, 30, 6 ft 3 in, 240 lb | 2,134 |
This table uses Mifflin-St Jeor. It shows why a value such as 1,000 can result from the inputs and formula without establishing a health judgement. Talk to a qualified clinician or registered dietitian before making significant changes to what you eat.
What BMR does not tell you
BMR is not a measurement of your actual energy use. It is an estimate generated by an equation, and a different equation can give a different result. BMR is not a daily total. It excludes movement, including exercise, so it is not the same number as TDEE. It is also not an intake target. A BMR figure says nothing about health on its own, and it cannot diagnose a medical condition. Changing the formula or rounding the inputs changes the output without changing the body. The most useful interpretation is narrow: BMR is a predicted resting figure based on the inputs and formula used.
Frequently asked questions
Does BMR include exercise?
No. BMR is the resting estimate, while exercise is part of movement across the day. TDEE includes all movement through its activity factor.
Which BMR formula is most accurate?
No formula is best for everyone. For overweight and obese adults, the Academy of Nutrition and Dietetics names Mifflin-St Jeor when RMR cannot be measured: it is within 10% of measured RMR in 70% of obese individuals. Harris-Benedict falls within 10% of measured RMR in 39-64% of obese individuals (Academy of Nutrition and Dietetics).
Can I calculate BMR without knowing my body fat percentage?
Yes. Mifflin-St Jeor and Harris-Benedict do not need body fat percentage. Katch-McArdle does, because it uses lean body mass.
Why do BMR calculators give different numbers?
They can use different formulas, rounding and unit conversions. The worked example above applies three formulas to one body and gives results from 1,742 to 1,835.
Sources
- Mifflin et al. Am J Clin Nutr 1990;51(2):241-7.
- Roza AM, Shizgal HM. Am J Clin Nutr 1984;40(1):168-82.
- Harris and Benedict, Carnegie Publication 279, 1919.
- Pavlidou et al. Metabolites 2023;13(2):189.
- Academy of Nutrition and Dietetics EAL, AWM: Determination of RMR.
- McArdle, Katch and Katch, Exercise Physiology
This calculator provides general information, not medical or nutritional advice. It does not diagnose or treat any condition. Talk to a qualified clinician or registered dietitian before making significant changes to what you eat.
Written by the Maintenance Calorie Calculator editorial team.