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FitCalcs

BMR Calculator

Find out how many calories your body burns at complete rest. Enter your stats to get your Basal Metabolic Rate from two established formulas, plus estimated maintenance calories for every activity level.

Sex

Enter your stats to see your BMR.

  1. Select your sex. Choose male or female — the BMR formulas apply a different constant for each.
  2. Enter your age, height, and weight. Use metric or imperial units; the calculator converts internally.
  3. Read your BMR. You get results from both the Mifflin-St Jeor and Harris-Benedict formulas, plus their average and a table of estimated maintenance calories at different activity levels.

Your Basal Metabolic Rate is the number of calories your body needs just to stay alive — breathing, circulating blood, maintaining body temperature, and repairing cells — with no movement at all. It is the largest single component of your total calorie burn, typically making up 60-75% of TDEE for most people.

What BMR does not tell you is how many calories you should eat. For that you need TDEE — your maintenance calories — which multiplies BMR by an activity factor. The activity table in the results panel is a shortcut to that number. For a full breakdown with macros, the TDEE and Macro calculators go further.

Both formulas estimate BMR from weight, height, age, and sex, but they were developed in different eras using different populations. The original Harris-Benedict equations were published in 1919 and revised by Roza and Shizgal in 1984. Mifflin-St Jeor came later, in 1990, and used a broader dataset that is more representative of modern Western adults.

A 2005 analysis in the Journal of the American Dietetic Association compared five common BMR equations and found Mifflin-St Jeor to be the most accurate on average, particularly for non-obese adults. Harris-Benedict tends to run about 5% higher. This calculator shows both and uses the average, which smooths out the bias of either formula alone.

BMR is not fixed. It is driven primarily by how much metabolically active tissue — mainly muscle — your body carries. As people age, they typically lose muscle mass, which gradually lowers BMR. Losing weight also lowers BMR because there is simply less tissue to maintain.

Extended calorie restriction can lower BMR beyond what weight loss alone would predict, through a process called metabolic adaptation. The body becomes more efficient at running on fewer calories, which is one reason weight loss often plateaus. Resistance training and keeping protein intake adequate are the main tools for minimizing this effect.

Mifflin-St Jeor (1990)

Men:   BMR = 10 x weight(kg) + 6.25 x height(cm) - 5 x age + 5
Women: BMR = 10 x weight(kg) + 6.25 x height(cm) - 5 x age - 161
BMR
= basal metabolic rate, in calories/day
weight
= body weight in kilograms
height
= height in centimeters
age
= age in years

Mifflin-St Jeor is considered the most accurate formula for most non-obese adults per a 2005 Academy of Nutrition and Dietetics review.

Harris-Benedict (revised Roza-Shizgal, 1984)

Men:   BMR = 88.362 + 13.397 x weight(kg) + 4.799 x height(cm) - 5.677 x age
Women: BMR = 447.593 + 9.247 x weight(kg) + 3.098 x height(cm) - 4.330 x age
BMR
= basal metabolic rate, in calories/day
weight
= body weight in kilograms
height
= height in centimeters
age
= age in years

The original Harris-Benedict equations (1919) were revised by Roza and Shizgal in 1984. This formula tends to run about 5% higher than Mifflin-St Jeor.

What is BMR?

BMR stands for Basal Metabolic Rate — the number of calories your body burns just to keep you alive at complete rest. It covers breathing, circulation, cell repair, and maintaining body temperature. BMR does not include any movement, exercise, or digestion. It is the floor below which your calorie intake should rarely go.

What is the difference between BMR and TDEE?

BMR is your calorie burn at complete rest; TDEE (Total Daily Energy Expenditure) adds the calories you burn through movement and exercise. TDEE is your maintenance — the amount you need to eat to keep your weight stable. BMR is typically 60-75% of TDEE for moderately active people.

Which BMR formula is more accurate — Mifflin-St Jeor or Harris-Benedict?

Mifflin-St Jeor (1990) is generally considered more accurate for most adults because it was developed using a larger, more representative dataset. A 2005 review in the Journal of the American Dietetic Association found Mifflin to be the most reliable for non-obese adults. Harris-Benedict (revised 1984) tends to run slightly higher. This calculator shows both and averages them as a practical middle ground.

Can I use BMR to plan my diet?

BMR tells you the minimum your body needs at rest, but your actual intake target should be based on TDEE — your maintenance calories — adjusted up or down for your goal. The activity table shown alongside your BMR result is a quick estimate of your TDEE at different activity levels. For a detailed macro breakdown, use the TDEE or Macro calculator.

Why does my BMR seem high or low?

BMR is driven by body size and composition. Larger, heavier people burn more calories at rest simply because there is more tissue to maintain. Muscle burns more energy than fat, so two people of the same weight with different body compositions will have different BMRs. Age also lowers BMR slightly as muscle mass tends to decline over time.

Does eating less lower my BMR?

Yes, significantly restricting calories over time causes the body to adapt by reducing its resting metabolic rate — sometimes called adaptive thermogenesis or metabolic adaptation. This is one reason very low-calorie diets often become less effective over time. Maintaining muscle mass through adequate protein and resistance training helps slow this effect.

How often should I recalculate my BMR?

Recalculate whenever your weight changes by around 5 kg (10 lbs) or more, or if your age has increased by several years. BMR changes gradually with body weight, so frequent recalculation is not necessary unless you are actively gaining or losing weight.

Is BMR the same as resting metabolic rate (RMR)?

They are closely related but not identical. BMR is measured under strict laboratory conditions — lying still, fasted, in a temperature-controlled environment. RMR is measured under less strict conditions and is typically 10-20% higher than BMR because it includes some light movement and digestion effects. Most online calculators, including this one, calculate BMR but the practical difference for everyday diet planning is small.

References

FitCalcs calculators provide general estimates for healthy adults and are not medical advice.

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