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BMR calculator

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Using this BMR calculator, estimate your basal metabolic rate (BMR) – the calories your body uses at rest – and daily calorie needs by activity level.

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ages 15 – 80
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Results unit

BMR estimation formula

%
for Katch-McArdle

Result

Daily calorie needs based on activity level

Activity LevelCalories
  • Exercise: 15–30 minutes of elevated heart rate activity.
  • Intense exercise: 45–120 minutes of elevated heart rate activity.
  • Very intense exercise: 2+ hours of elevated heart rate activity.

BMR is estimated with the selected equation. Daily calorie needs are BMR multiplied by an activity factor. These are estimates only and are not medical advice.

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Fat intake calculatorProtein calculatorCarbohydrate calculatorMacro calculator

Basal metabolic rate (BMR)

Basal metabolic rate, or BMR, is an estimate of how much energy your body uses each day to keep essential processes running while you are at complete rest. Even when you are not moving, your body needs energy to breathe, circulate blood, regulate temperature, support the brain and nervous system, repair cells, and maintain the function of organs such as the heart, liver, and kidneys.

BMR is expressed in kilocalories per day, usually written simply as calories per day. It is generally the largest component of daily energy expenditure, but it does not represent all the calories you burn in a normal day.

BMR, RMR, and daily calorie needs

These terms are closely related, but they are not identical:

  • Basal metabolic rate (BMR) is measured under tightly controlled conditions. The person is awake, fully rested, fasted, and in a comfortable temperature-controlled environment.
  • Resting metabolic rate (RMR), also called resting energy expenditure, is measured under less restrictive conditions. It is often slightly higher than BMR because it may include small amounts of movement and recent daily activity.
  • Total daily energy expenditure (TDEE) is the total energy used over an entire day. It includes resting metabolism, physical activity, everyday movement, and the energy required to digest and process food.

Online calculators usually estimate BMR or RMR with a prediction equation. To estimate maintenance calories, the resting estimate is then adjusted for activity. This means that a BMR result should not be interpreted as the number of calories you burn during a typical day or automatically used as a daily calorie target.

How is BMR estimated?

BMR cannot be calculated exactly from height and weight alone. Instead, calculators use equations developed from measurements collected from groups of people. The result is a practical estimate, and an individual’s actual resting energy expenditure may be higher or lower.

Mifflin–St Jeor equation

The Mifflin–St Jeor equation is widely used to estimate resting energy expenditure in adults.

For men:

BMR = (10 × W) + (6.25 × H) − (5 × A) + 5

For women:

BMR = (10 × W) + (6.25 × H) − (5 × A) − 161

Revised Harris–Benedict equation

The original Harris–Benedict equations were developed in the early twentieth century and were later recalculated using a larger set of observations.

For men:

BMR = 88.362 + (13.397 × W) + (4.799 × H) − (5.677 × A)

For women:

BMR = 447.593 + (9.247 × W) + (3.098 × H) − (4.330 × A)

Katch–McArdle equation

The Katch–McArdle equation uses lean body mass rather than separate sex-specific constants:

BMR = 370 + (21.6 × L)

Lean body mass can be estimated as:

L = W × (1 − body fat percentage ÷ 100)

In these formulas:

  • W = weight in kilograms
  • H = height in centimeters
  • A = age in years
  • L = lean body mass in kilograms

The Katch–McArdle method may be useful when a reasonably accurate body-fat estimate is available. However, errors in the body-fat measurement flow directly into the BMR estimate. For most adults who do not know their body-fat percentage, the Mifflin–St Jeor equation is a practical starting point. The equations use male and female categories because that is how their underlying data were modeled; they may be less precise when those categories do not represent an individual’s physiology or body composition well.

What affects BMR?

Resting energy expenditure varies from person to person. Important influences include:

  • Body size: A larger body generally requires more energy to maintain, so height and weight are included in common equations.
  • Body composition: Fat-free mass includes muscle, organs, bone, water, and other non-fat tissue. Because these tissues use different amounts of energy, two people of the same weight can have different metabolic rates.
  • Age: Resting energy expenditure often decreases with age, partly because body composition and metabolically active tissue change over time.
  • Growth, pregnancy, and breastfeeding: Energy requirements can change during periods when the body is supporting growth or milk production. Standard adult BMR equations are not designed to determine calorie needs during pregnancy or breastfeeding.
  • Illness and recovery: Fever, infection, injury, surgery, and some chronic conditions can alter energy use.
  • Hormones and medications: Thyroid function and certain medications can affect metabolism. A calculator cannot diagnose a hormonal or metabolic condition.
  • Energy restriction and weight change: As body weight falls, a smaller body generally requires less energy. The body may also adapt to a sustained energy deficit, so actual expenditure can decline by more than a basic equation predicts.
  • Genetics and individual variation: People with similar age, size, and body composition may still have different resting energy needs.

Short-term factors such as recent exercise, food intake, caffeine, nicotine, stress, sleep, and room temperature can also affect a resting measurement. This is one reason laboratory testing follows a standardized protocol.

From BMR to total daily energy expenditure

Your body uses energy in several ways:

  1. Resting metabolism supports basic biological functions.
  2. The thermic effect of food is the energy used to digest, absorb, and process nutrients.
  3. Exercise activity includes planned activities such as walking, running, cycling, or strength training.
  4. Non-exercise activity includes standing, household tasks, commuting, fidgeting, and other everyday movement.

A calorie calculator may estimate TDEE by multiplying BMR by an activity factor. These factors are convenient, but activity levels can be difficult to classify and may vary substantially from one day to another. Someone with a desk job who trains several times a week may have a different total expenditure from someone who does not formally exercise but performs physical work throughout the day.

For that reason, estimated maintenance calories are best treated as a starting point. Tracking average food intake and body-weight trends over several weeks can help show whether the estimate is too high, too low, or reasonably close. Day-to-day weight changes often reflect water, sodium, stored carbohydrate, and digestive contents rather than immediate changes in body fat, so trends are more informative than a single reading.

Can you change your BMR?

BMR is not a fixed number, but most methods advertised as quick “metabolism boosters” have a small or temporary effect. Gaining fat-free mass can raise resting energy use, although the size of the increase varies and is often modest. Regular resistance training can help build or preserve muscle, while aerobic activity can increase total daily expenditure and support cardiovascular health even if it does not greatly change BMR.

Changes in body weight also change energy requirements. During weight loss, BMR usually decreases because there is less body tissue to maintain, and metabolic adaptation may reduce expenditure further. Extreme dieting is not a reliable way to improve metabolism and can make a nutrition plan difficult to sustain.

How accurate is a BMR calculator?

A BMR calculator is useful for planning, but its answer is not a direct measurement. Prediction equations describe average relationships in the populations from which they were developed. Accuracy may be lower for people with unusually high or low muscle mass, older adults, growing adolescents, pregnant or breastfeeding people, elite athletes, and people with certain medical conditions.

Resting energy expenditure can be measured more directly with indirect calorimetry, which estimates energy use from oxygen consumption and carbon dioxide production. This type of test is available in some hospitals, clinics, sports laboratories, and dietetic practices. Even measured values can vary with testing conditions, so preparation and protocol matter.

Using your result safely

Think of your calculated BMR as a reference point—not a diagnosis, a guaranteed maintenance level, or a universal minimum amount you must eat. Your actual needs depend on activity, health, goals, and individual physiology. If you are planning a major calorie restriction, are pregnant or breastfeeding, are under 18, have an eating-disorder history, take medication that affects weight or metabolism, or have a condition such as diabetes or thyroid disease, seek advice from a physician or registered dietitian.

Frequently asked questions:

Is a higher BMR better?

Not necessarily. A higher result generally means that the body uses more energy at rest, often because the person has a larger body or more fat-free mass. BMR is not a score of health or fitness.

Does eating below BMR stop weight loss?

No single calorie threshold causes the body to stop losing weight. However, a large or prolonged energy deficit can produce metabolic adaptation, fatigue, nutrient shortfalls, loss of lean tissue, and difficulty maintaining the plan. A BMR estimate should not be used by itself to design an aggressive diet.

Why do different calculators give different answers?

Calculators may use different equations, rounding rules, units, body-fat estimates, or activity multipliers. Small differences are normal and reinforce that the result is an estimate.

How often should BMR be recalculated?

Recalculate after a meaningful change in weight or body composition. There is usually little value in recalculating after ordinary day-to-day weight fluctuations.

Is BMR the number of calories needed to maintain weight?

No. Weight maintenance depends on total daily energy expenditure, which includes BMR plus digestion, exercise, and all other movement.

References

This calculator provides general educational information and is not a substitute for individualized medical or nutrition advice.