BMR Calculator

Your BMR is the energy you would burn in a day doing nothing but staying alive. Enter your stats to estimate it with the Mifflin-St Jeor equation.

The Mifflin-St Jeor equation

For weight in kilograms, height in centimetres, and age in years:

Men: BMR = (10 × weight) + (6.25 × height) − (5 × age) + 5
Women: BMR = (10 × weight) + (6.25 × height) − (5 × age) − 161

The result is calories per day. It assumes you are awake but completely at rest, comfortably warm, and have not eaten in several hours. Real resting burn varies with muscle mass, hormones (thyroid especially), genetics, and even the outside temperature, so treat the number as a solid estimate — good to within about 10 percent for most people — rather than a precise measurement.

Worked example

A 30-year-old man, 180 cm, 80 kg: BMR = (10 × 80) + (6.25 × 180) − (5 × 30) + 5 = 800 + 1,125 − 150 + 5 = 1,780 calories/day. A 30-year-old woman with the same height and weight: 1,780 − 5 − 161 = 1,614 calories/day — the gap is mostly the sex constant plus, in real life, lower average muscle mass.

Roughly what to expect

Profile	Approx. BMR
Woman, 25, 165 cm, 60 kg	~1,370 kcal
Woman, 45, 168 cm, 75 kg	~1,480 kcal
Man, 25, 178 cm, 75 kg	~1,750 kcal
Man, 45, 180 cm, 90 kg	~1,830 kcal

Mifflin-St Jeor vs Harris-Benedict vs Katch-McArdle

Harris-Benedict (revised 1984) is the classic equation but tends to run 5 percent high for today's population.Katch-McArdle uses your lean body mass instead of total weight, so it is more accurate if you know your body fat percentage — useful for very lean or very muscular people. For everyone else, Mifflin-St Jeor is the best free choice and the one this calculator uses.

Using your BMR

On its own, BMR is not a calorie target — nobody lies still all day. Multiply it by an activity factor to get maintenance calories with the TDEE calculator, then adjust up or down for a goal with the calorie calculator, and split the target into protein, carbs and fat with the macro calculator.

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Frequently asked questions

What is BMR?

Basal metabolic rate is the number of calories your body uses at complete rest to keep basic functions running — breathing, circulation, cell repair, brain activity, keeping warm. It is the largest single part of daily calorie burn, usually 60 to 70 percent of the total.

Which equation does this use, and why?

The Mifflin-St Jeor equation, published in 1990. It is the equation most dietitians use today because it predicts measured resting energy expenditure more accurately than the older Harris-Benedict equation (1919) for the modern general population, typically within about 10 percent.

What is the difference between BMR, RMR and TDEE?

BMR is measured under strict lab conditions (fasted, fully rested, thermally neutral). RMR (resting metabolic rate) is measured under looser conditions and runs a few percent higher; the two terms are often used interchangeably. TDEE is BMR (or RMR) multiplied by an activity factor to include movement, exercise, and the energy used to digest food — that is the number you use to plan calories.

Why does age lower BMR?

Resting metabolism falls roughly 1 to 2 percent per decade in adulthood, mainly because people lose muscle over time and muscle burns more energy at rest than fat does. Staying strong with resistance training slows the decline.

Can I raise my BMR?

Somewhat, and slowly. More muscle raises resting burn, but each kilogram of added muscle only adds roughly 10 to 15 calories a day — real but modest. Crash dieting does the opposite: severe, prolonged calorie restriction can suppress BMR by 5 to 15 percent (adaptive thermogenesis). Eating enough, training, and sleeping well all help keep it up.

Why is my BMR different from a smartwatch or scale reading?

Bioimpedance scales and wearables estimate BMR from body-composition guesses and generic models, and can disagree with an equation by 100 to 300 calories. A metabolic cart test (indirect calorimetry) at a clinic is the accurate measurement; the equation here is the best free approximation.

Should I ever eat below my BMR?

As a rule, no. Eating below BMR for extended periods makes nutrient targets hard to meet and accelerates muscle loss. Create a deficit by eating below your TDEE, not below your BMR — see the calorie calculator.

Last reviewed: September 2026. Figures and formulas are checked against their published sources; see the site's data notes.