BMR Calculator

Basal Metabolic Rate (BMR) Calculator

Estimate your basal metabolic rate (BMR) and daily calorie needs with the Mifflin-St Jeor equation.

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Enter your sex, age, height and weight, then select Calculate BMR to see your resting and daily calorie estimates.

What Is Basal Metabolic Rate?

This basal metabolic rate (BMR) calculator estimates the calories your body burns at complete rest, before any movement, exercise or digestion is counted. Your basal metabolic rate (BMR) covers breathing, circulation, temperature regulation and cell repair, and it is usually the largest single part of your daily energy use.

Enter your sex, age, height and weight in US or metric units and the BMR calculator applies the Mifflin-St Jeor equation, the formula most widely used in current nutrition practice. It then estimates your total daily energy expenditure (TDEE) across five activity levels so you can see roughly how many calories you need each day.

Understanding Your Basal Metabolic Rate Result

Your BMR result is the estimated number of calories needed each day to keep essential functions running if you stayed completely at rest. It is close to, but not identical with, resting energy expenditure (RMR), which is measured under slightly less strict conditions and is usually a little higher.

On its own, BMR is not a calorie target. Daily calorie needs come from BMR multiplied by an activity factor, which is what the TDEE figures below your result show. Eating around your TDEE tends to maintain weight, eating below it tends to produce weight loss, and eating above it tends to produce weight gain - always at an individual rate that depends on adherence, body composition, medication, sleep and other factors.

How Is Basal Metabolic Rate Calculated?

Mifflin-St Jeor: BMR = (10 x weight_kg) + (6.25 x height_cm) - (5 x age) + 5 (male) or - 161 (female)

Mifflin-St Jeor Equation

The Mifflin-St Jeor equation estimates BMR from weight in kilograms, height in centimetres, age in years and sex:

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

The older Harris-Benedict equation (and its 1984 Roza revision) uses the same inputs with different coefficients and generally returns a slightly higher basal metabolic rate. Where body fat percentage is known, the Katch-McArdle formula estimates BMR from lean body mass instead. This calculator uses Mifflin-St Jeor because it has performed best in validation studies of healthy adults.

BMR vs TDEE

BMR is energy used at rest. TDEE is BMR plus everything else: the thermic effect of food, non-exercise movement such as walking and fidgeting, and deliberate exercise.

TDEE is estimated by multiplying BMR by an activity factor, roughly 1.2 for sedentary through to about 1.9 for very heavy training or physical work. Because the multiplier is a broad category rather than a measurement, TDEE is less precise than BMR. Use it as a starting point, then adjust based on two to four weeks of real weight and intake data.

How to Interpret Your BMR

Treat the number as an estimate with a realistic margin of error - published comparisons of predictive equations against measured metabolic testing commonly differ by roughly 10 percent in either direction for individuals.

A higher BMR usually reflects a larger body size or more lean mass rather than a faster metabolism in any medical sense. BMR also tends to fall slowly with age and with weight loss. If you are tracking a goal, the practical use of BMR is as an input to your TDEE and calorie target, not as a score to optimise.

Methodology

This calculator uses the Mifflin-St Jeor equation, published in 1990, which is widely used to estimate resting energy expenditure in healthy adults. Imperial inputs are converted to metric before the equation is applied (1 in = 2.54 cm, 1 lb = 0.45359237 kg).

Worked Example

A 35-year-old male who is 5 ft 10 in (177.8 cm) and 180 lb (81.65 kg): BMR = (10 x 81.65) + (6.25 x 177.8) - (5 x 35) + 5 = 816.5 + 1111.25 - 175 + 5 = 1,758 calories per day.

Important Limitations

These figures are estimates produced by a population equation. They do not account for body composition, thyroid function, medication, pregnancy, illness or training history. They are informational only and are not medical advice. Talk with a qualified healthcare professional before making changes to your diet.

Frequently Asked Questions

What is basal metabolic rate?
Basal metabolic rate is the number of calories your body uses at complete rest to sustain essential functions such as breathing, circulation, brain activity, temperature regulation and cell repair. For most people it accounts for the largest share of daily energy use.
What is a BMR calculator?
A BMR calculator is a tool that estimates your basal metabolic rate from your sex, age, height and weight using a validated predictive equation. This basal metabolic rate calculator uses the Mifflin-St Jeor equation and also estimates daily calorie needs at five activity levels.
How is BMR calculated?
This calculator uses Mifflin-St Jeor: for men, BMR = (10 x kg) + (6.25 x cm) - (5 x age) + 5; for women, BMR = (10 x kg) + (6.25 x cm) - (5 x age) - 161. US units are converted to kilograms and centimetres before the formula is applied.
How accurate is a BMR calculation?
Predictive equations are estimates. Validation studies of healthy adults commonly find individual results within about 10 percent of measured values, with larger errors at the extremes of body size or in metabolic disease. Indirect calorimetry is the only way to measure your BMR directly.
What is the Mifflin-St Jeor equation?
It is a predictive BMR equation published in 1990 that estimates resting energy needs from weight, height, age and sex. It is widely used in dietetic practice because it has generally outperformed older equations such as Harris-Benedict in healthy adults.
What is the difference between BMR and TDEE?
BMR is the energy used at rest. TDEE, or total daily energy expenditure, is BMR plus digestion, daily movement and exercise. TDEE is estimated by multiplying BMR by an activity factor and is what most calorie targets are based on.
Does BMR change with age?
Yes. Basal metabolic rate generally declines gradually through adulthood, largely because lean body mass tends to decrease. The age term in the Mifflin-St Jeor equation reflects this trend, though individual change varies.
Does body weight affect BMR?
Yes. Larger bodies have more metabolically active tissue, so a higher weight generally raises BMR. Lean mass raises it more per kilogram than fat mass, which is why body-composition based formulas such as Katch-McArdle can differ from Mifflin-St Jeor.

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