BMR Calculator

Your basal metabolic rate (BMR) is the calories your body burns at complete rest. By the Mifflin-St Jeor equation, BMR = 10 × kg + 6.25 × cm − 5 × age + 5 for men (−161 for women), so a 30-year-old man who is 175 cm and 70 kg burns about 1,649 kcal a day.

By the Calculators With Steps team · Updated November 10, 2026 · How we check our math

Your BMR (Mifflin-St Jeor)

1,649 kcal/day

calories your body burns at complete rest

Revised Harris-Benedict (1984): 1,696 kcal+47 kcal vs Mifflin-St Jeor
Katch-McArdle: Add body fat %uses lean body mass instead of weight
Range across formulas: 1,649 – 1,696 kcal
BMR per hour: 69 kcal/hMifflin-St Jeor ÷ 24

Step-by-step working

Mifflin-St Jeor: 10 × 70 + 6.25 × 175 − 5 × 30 + 5 = 1,648.75 kcal/day
Revised Harris-Benedict: 88.362 + 13.397 × 70 + 4.799 × 175 − 5.677 × 30 = 1,695.67 kcal/day
Katch-McArdle needs your body fat %: BMR = 370 + 21.6 × lean body mass (kg).

Calories per day by activity level (BMR × activity factor)

Activity level	Factor	Calories per day
Sedentary: desk job, little or no exercise	× 1.2	1,979 kcal
Lightly active: light exercise or sport 1–3 days a week	× 1.375	2,267 kcal
Moderately active: moderate exercise 3–5 days a week	× 1.55	2,556 kcal
Very active: hard exercise 6–7 days a week	× 1.725	2,844 kcal
Extra active: very hard training or a physical job, often twice a day	× 1.9	3,133 kcal

BMR is energy for breathing, circulation and organ function at complete rest. It is not your daily calorie need; multiply by an activity factor (table above) or use the TDEE calculator for that. Equations are estimates; a lab test (indirect calorimetry) measures it directly.

How to use the BMR calculator

Choose Metric or US units.
Enter your sex, age, height and weight.
If you know your body fat percentage, add it to unlock the Katch-McArdle result. Leave it blank otherwise.

The main result is your BMR from the Mifflin-St Jeor equation. Alongside it you’ll see the revised Harris-Benedict and Katch-McArdle results, the range across formulas, and a table converting your BMR into daily calories at each activity level.

BMR formulas

Mifflin-St Jeor (1990)

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

Revised Harris-Benedict (Roza and Shizgal, 1984)

Men: BMR = 88.362 + 13.397 × weight + 4.799 × height − 5.677 × age
Women: BMR = 447.593 + 9.247 × weight + 3.098 × height − 4.330 × age

Katch-McArdle

BMR = 370 + 21.6 × lean body mass (kg), where lean body mass = weight × (1 − body fat %)

Weight is in kilograms, height in centimetres and age in years. In US units the calculator converts pounds and inches first.

Worked example

Two adults, both 30 years old:

Formula	Man: 175 cm, 70 kg, 18% fat	Woman: 160 cm, 55 kg, 25% fat
Mifflin-St Jeor	1,648.75 kcal	1,239 kcal
Revised Harris-Benedict	1,695.67 kcal	1,321.96 kcal
Katch-McArdle	1,609.84 kcal	1,261 kcal

For the man, Katch-McArdle uses lean mass of 70 × 0.82 = 57.4 kg, so 370 + 21.6 × 57.4 = 1,609.84 kcal. The three answers span less than 90 kcal for him. For the woman, Harris-Benedict comes out 83 kcal above Mifflin-St Jeor, a typical gap.

Which BMR formula should you use?

Mifflin-St Jeor is the best default. It was built from measurements of 498 healthy adults, and a 2005 review in the Journal of the American Dietetic Association found it the most reliable of the common equations for both non-obese and obese adults.
Harris-Benedict dates from 1919 and was refitted by Roza and Shizgal in 1984. It is still widely used in hospitals and on older websites, and tends to give slightly higher numbers than Mifflin-St Jeor.
Katch-McArdle ignores age and sex and uses only lean mass. It suits very lean, very muscular or very heavy people, for whom weight alone is misleading, but it is only as good as your body fat number. Tape, calipers and smart scales can be off by several percentage points.

When the formulas disagree a lot, the truth is usually somewhere in the middle, and your weight trend over a few weeks is the final judge.

What affects your BMR

Lean mass. Muscle and organs burn more energy than fat, which is why bigger and more muscular people have a higher BMR.
Age. Mifflin-St Jeor takes off 5 kcal for every year. The 70 kg man above drops from 1,649 kcal at 30 to 1,599 kcal at 40 and 1,549 kcal at 50, assuming nothing else changes.
Sex. At the same size, men’s BMR is higher, mainly because of more lean mass.
Hormones and health. Thyroid problems, fever, pregnancy and some medicines can push BMR up or down. If your weight changes without a clear reason, see a doctor.

From BMR to daily calories

BMR is not how much you should eat. To get your daily burn, multiply by an activity factor. For the 30-year-old man with a BMR of 1,648.75 kcal, that gives 1,979 kcal if sedentary, 2,267 kcal if lightly active, 2,556 kcal if moderately active, 2,844 kcal if very active and 3,133 kcal if extra active. The TDEE calculator does this for you and shows where the calories go, and the calorie calculator turns it into targets for losing or gaining weight.

If you want to use Katch-McArdle but don’t know your body fat, the body fat calculator estimates it from tape measurements.

BMR Calculator: frequently asked questions

What is BMR?

BMR, or basal metabolic rate, is the energy your body uses at complete rest to keep your heart beating, lungs breathing, brain working and body warm. It is the largest part of daily energy use for most people, but it does not include digestion, movement or exercise.

How do I calculate my BMR?

The most widely recommended formula is Mifflin-St Jeor: 10 × weight (kg) + 6.25 × height (cm) − 5 × age, then + 5 for men or − 161 for women. A 30-year-old man who is 175 cm tall and weighs 70 kg has a BMR of 700 + 1,093.75 − 150 + 5 = 1,648.75 kcal a day.

How do I calculate BMR for a woman?

Use the same Mifflin-St Jeor formula but subtract 161 instead of adding 5. A 30-year-old woman who is 160 cm and 55 kg has a BMR of 550 + 1,000 − 150 − 161 = 1,239 kcal a day. The revised Harris-Benedict formula gives 1,322 kcal for her.

Which BMR formula is the most accurate?

A 2005 systematic review by Frankenfield and colleagues found Mifflin-St Jeor predicted resting metabolic rate within 10% of measured values in more people than other common equations, including Harris-Benedict. Katch-McArdle can do better for very lean or muscular people if you know your body fat accurately.

Does BMR decrease with age?

Yes. In the Mifflin-St Jeor equation each year of age lowers BMR by 5 kcal, so the same 175 cm, 70 kg man drops from 1,649 kcal at 30 to 1,549 kcal at 50. Real-world declines also come from losing muscle, which strength training can slow.

What is the difference between BMR and RMR?

BMR is measured under strict conditions: just after waking, after a 12-hour fast, lying still in a warm, quiet room. Resting metabolic rate (RMR) uses looser conditions and is usually slightly higher. Calculators treat the two as roughly the same number.

Can I increase my BMR?

Building muscle raises it modestly. In the Katch-McArdle formula each extra kilogram of lean mass adds 21.6 kcal a day. Crash dieting does the opposite, because losing muscle lowers BMR.

Disclaimer: This tool gives general estimates for information only and is not medical advice. Individual needs vary with health conditions, medications, pregnancy and other factors, so talk to a doctor or registered dietitian before you change your diet, exercise or treatment.

How we checked this page: every figure in the examples and FAQs above is produced by this calculator and verified by automated tests against known answers, and the rules and rates come from the sources below. Last updated November 10, 2026. Spotted a problem? Tell us.

Sources and further reading