BMR Calculator – Basal Metabolic Rate (3 Formulas)

Your basal metabolic rate (BMR) is the number of calories your body uses in 24 hours at complete rest, just to keep you alive: breathing, circulating blood, keeping warm and running your organs. It is usually the largest part of your daily energy use, and it is the starting point for any calorie target.

How to use the BMR calculator

Choose metric or US units.
Select your sex and enter your age.
Enter your height and weight.
Optionally enter your body fat percentage to get a Katch-McArdle result.

The calculator shows your BMR from each formula plus the calories you burn per hour at rest. Expect the formulas to differ by up to about 100 kcal. That spread is a fair picture of how precise any estimate can be.

The three BMR formulas

Mifflin-St Jeor (1990)

This is the formula used in the main result, because studies have found it the most accurate for the general population.

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 (1984)

The original 1919 Harris-Benedict equation was updated by Roza and Shizgal in 1984. It tends to give slightly higher numbers than Mifflin-St Jeor.

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

Katch-McArdle

This formula ignores sex and age and uses lean body mass instead, which makes it useful for athletes.

BMR = 370 + 21.6 × lean body mass(kg)
Lean body mass = weight × (1 − body fat % ÷ 100)

Worked example

A 35-year-old man, 180 cm tall, weighing 80 kg with 20% body fat:

Mifflin-St Jeor: 10 × 80 + 6.25 × 180 − 5 × 35 + 5 = 800 + 1,125 − 175 + 5 = 1,755 kcal/day
Harris-Benedict: 88.362 + 1,071.76 + 863.82 − 198.70 ≈ 1,825 kcal/day
Katch-McArdle: lean mass = 80 × 0.8 = 64 kg, so 370 + 21.6 × 64 ≈ 1,752 kcal/day

At rest, he burns about 1,755 ÷ 24 ≈ 73 kcal an hour.

A 30-year-old woman, 165 cm and 62 kg, has a Mifflin-St Jeor BMR of 620 + 1,031.25 − 150 − 161 ≈ 1,340 kcal/day.

What affects your BMR

Body size. More body mass needs more energy to maintain.
Muscle mass. Muscle burns more energy at rest than fat tissue.
Age. BMR drops gradually, about 5 kcal a day per year in the Mifflin-St Jeor formula, partly because muscle mass tends to fall.
Sex. Men usually have a higher BMR at the same height and weight, mostly because of greater muscle mass.
Other factors. Thyroid function, illness, pregnancy, genetics and very low calorie diets can all move your real BMR away from the estimate.

BMR versus TDEE

BMR assumes you spend the whole day lying still. Your total daily energy expenditure (TDEE) adds everything else: walking, working, exercise and the energy used to digest food. TDEE is BMR multiplied by an activity factor between about 1.2 for desk-bound people and 1.9 for very active ones. For the man in the example, that means roughly 2,100 to 3,300 kcal a day.

Tips for using your BMR

Treat it as an estimate. Formulas are based on population averages. Your real BMR may differ by 10% or more.
Use it as a floor, not a target. For weight loss, eat below your TDEE but generally not below your BMR.
Recalculate as you change. Your BMR falls as you lose weight, so update your numbers every few kilograms.
Lab tests are more precise. Indirect calorimetry, which measures the oxygen you use, gives a direct measurement if you need one.

This calculator gives general information and is not medical advice. Talk to a doctor or registered dietitian before major changes to your diet.

Frequently asked questions

What is a good BMR?

There is no good or bad BMR. It mainly reflects your size, age, sex and muscle mass. A larger, more muscular person has a higher BMR than a smaller one, and BMR slowly falls with age.

Which BMR formula is the most accurate?

For most adults, Mifflin-St Jeor is the best-validated formula and is the one dietitians most often use. If you know your body fat percentage reliably, Katch-McArdle can be better for very lean or very muscular people.

Is BMR the same as the calories I burn per day?

No. BMR is only what you burn at complete rest. Your total daily energy expenditure adds the energy for movement, exercise and digesting food, and is usually 20–90% higher. Use our calorie calculator to estimate it.

Should I eat fewer calories than my BMR to lose weight?

Generally not without medical supervision. Eating well below your BMR for long periods can cost muscle, slow your metabolism and make it hard to get enough nutrients. A moderate deficit below your total daily needs works better.

Can I increase my BMR?

Building muscle through strength training raises BMR modestly, because muscle uses more energy at rest than fat. Age-related decline can also be slowed by staying active.

Last updated October 28, 2026 · By the ZTool team