BMR Calculator

BMR calculator at a glance#

What is BMR?#

Basal metabolic rate (BMR) is the number of calories your body burns in a day at rest, just to keep running: breathing, circulating blood, keeping warm. It doesn't include walking, exercise or digesting food.

How do you calculate BMR?#

The calculator's default is the Mifflin-St Jeor equation: 10 × weight in kg + 6.25 × height in cm − 5 × age in years, then + 5 for men or − 161 for women. Enter your sex, age, height and weight in pounds and feet or in kilograms and centimeters, and pick one of three formulas. The calculator gives your BMR in calories per day plus your daily calories at six activity levels.

What is a normal BMR for a woman?#

There's no single normal value, because BMR depends on weight, height and age as well as sex. A 35-year-old woman who is 5 ft 6 in (167.64 cm) and weighs 150 lb (68.04 kg) has a BMR of about 1,392 calories a day by Mifflin-St Jeor. A man with the same age, height and weight comes out at 1,558.

What BMR means#

Think of BMR as the cost of being alive before you move. Your heart, lungs, brain, liver and kidneys use energy around the clock, and the bigger your body, the more energy that takes. Everything else you burn in a day, from walking to the gym, sits on top of it.

The equations in this calculator predict that number from your body size instead of measuring it. Mifflin and St Jeor built theirs from the resting energy expenditure of 498 healthy adults, measured by indirect calorimetry, which works out energy use from your breathing. You'll also see the terms resting metabolic rate (RMR) and resting energy expenditure (REE). This calculator reports the equation's result as BMR.

We'll follow one person through the page: a 35-year-old woman, 5 ft 6 in (167.64 cm) tall, weighing 150 lb (68.04 kg).

The three BMR formulas in the calculator#

All three give calories per day. The first two use weight, height, age and sex. The third uses only your weight and body fat percentage.

Mifflin-St Jeor#

The equation comes from a 1990 study in the American Journal of Clinical Nutrition by Mifflin, St Jeor and colleagues. The 498 adults in it were 19 to 78 years old, 264 of them at a normal weight and 234 with obesity. The published equations are:

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

For the woman in our example, work out each term:

• Weight: 10 × 68.04 = 680.4
• Height: 6.25 × 167.64 = 1,047.75
• Age: 5 × 35 = 175, which is subtracted
• Sex: 161 is subtracted for women

Then add them up: 680.4 + 1,047.75 − 175 − 161 = 1,392.15, which the calculator shows as 1,392 calories per day. The calculator accepts ages 15 to 80, a little wider than the study's 19 to 78.

If you measure in US units, convert first. Divide pounds by 2.2046 to get kilograms (150 lb is 68.04 kg) and multiply inches by 2.54 to get centimeters (66 in is 167.64 cm). The calculator does this for you when you enter pounds, feet and inches.

Revised Harris-Benedict#

The Harris-Benedict equations date from 1919. The calculator uses the 1984 revision by Roza and Shizgal, who re-evaluated them with data from a wider range of ages:

• Men: BMR = 88.362 + 13.397 × weight (kg) + 4.799 × height (cm) − 5.677 × age
• Women: BMR = 447.593 + 9.247 × weight (kg) + 3.098 × height (cm) − 4.330 × age

For our example, 447.593 + 629.17 + 519.35 − 151.55 = 1,444.56, so the calculator shows 1,445. Roza and Shizgal reported that the equations predict resting energy expenditure in normally nourished people to within about 14% either way.

Katch-McArdle#

This formula skips sex, height and age. It works from lean body mass, your weight minus your fat: BMR = 370 + 21.6 × lean body mass (kg), the same form used in a 2025 study in Frontiers in Nutrition. The calculator gets lean mass from the body fat percentage you enter in the Options panel.

At 30% body fat, our example's lean mass is 68.04 × 0.70 = 47.63 kg. Then 370 + 21.6 × 47.628 = 1,398.76, shown as 1,399. The formula is only as good as the body fat figure you give it. If you don't have one, the body fat percentage calculator can give you a rough figure from your BMI, or from tape measurements of your neck and waist (and hips, for women).

The three results for our example are 1,392, 1,445 and 1,399 calories, which land within about 4% of each other.

BMR for women and men#

In Mifflin-St Jeor, the only difference between the sexes is the last term, + 5 for men and − 161 for women. Two people with the same weight, height and age always differ by 166 calories. Our 150 lb woman's BMR of 1,392 becomes 1,558 for a man of the same size. With revised Harris-Benedict the gap isn't fixed, because every coefficient changes, and for this body it's 1,445 for a woman and 1,606 for a man.

Age works the same way for everyone. In Mifflin-St Jeor each year lowers BMR by 5 calories, so ten years is 50 calories. At 45 our example would read 1,342. Each extra 10 lb (4.54 kg) adds about 45 calories.

From BMR to daily calories#

BMR alone is too low for a daily calorie target, because it leaves out all movement. Under your BMR, the calculator multiplies it by six activity factors and labels each row with an exercise pattern.

Each row is more exercise than the one above it, and the multiplier rises with it. For a target that goes one step further, the TDEE calculator applies the same kind of multiplier and then shows calorie levels for losing or gaining weight at set weekly rates.

This gives an estimate, not medical advice. A doctor can tell you what the number means for you.

How accurate is a BMR calculator?#

Any of these equations gives a population-based estimate, not a measurement. The 1984 Harris-Benedict revision was accurate to within about 14% for normally nourished adults, and the authors found it unreliable for malnourished patients. The National Academies' 2023 report on energy needs makes a similar point: actual energy needs vary even among people of the same sex, age, height, weight and activity level.

BMR by weight#

Here's the Mifflin-St Jeor BMR for a 35-year-old at 5 ft 6 in, for women and men, as the calculator shows it.

Sources#

• Mifflin MD, St Jeor ST, et al. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr, 1990
• Roza AM, Shizgal HM. The Harris Benedict equation reevaluated. Am J Clin Nutr, 1984
• National Academies, Dietary Reference Intakes for Energy (2023), chapter 7

Frequently asked questions#

What is the difference between BMR and RMR?#

Both describe the energy you use at rest. Basal metabolic rate is measured under stricter resting conditions than resting metabolic rate, and calculators often use the two terms interchangeably. The Mifflin-St Jeor equation was built from resting energy expenditure measurements, and this calculator reports its result as BMR.

Which BMR formula is most accurate?#

None is accurate for everyone. Mifflin-St Jeor is the calculator's default. In the 1990 study that produced it, the original 1919 Harris-Benedict equations overestimated measured resting energy by about 5%. Katch-McArdle depends on your body fat percentage, so a wrong body fat figure gives a wrong answer.

How do I calculate BMR as a woman?#

Use the women's Mifflin-St Jeor equation: 10 × weight (kg) + 6.25 × height (cm) − 5 × age − 161. For a 35-year-old woman at 68.04 kg and 167.64 cm, that's 680.4 + 1,047.75 − 175 − 161 = 1,392 calories per day.

What is a realistic BMR for a 28-year-old man?#

It depends on his size. A 28-year-old man who is 5 ft 10 in (177.8 cm) and weighs 160 lb (72.57 kg) has a Mifflin-St Jeor BMR of 1,702 calories a day: 725.7 + 1,111.25 − 140 + 5. Put in your own numbers above for yours.

Does BMR go down with age?#

In these equations, yes. Mifflin-St Jeor takes off 5 calories for every year of age, and revised Harris-Benedict takes off 5.677 for men and 4.330 for women. Weight and height count too, so a change in weight shifts BMR as well.

Is my BMR the number of calories I should eat?#

No. BMR covers only what your body uses at rest. Your daily needs include all your movement on top, which is why the calculator lists BMR times 1.2 to 1.9 under the result. The calorie calculator turns that into daily calories for losing, keeping or gaining weight.