BMR Calculator — Step-by-Step Solutions

The BMR Calculator estimates your Basal Metabolic Rate — the number of calories your body needs at complete rest to maintain basic functions like breathing and circulation. It uses three established formulas: Mifflin-St Jeor, Harris-Benedict, and Katch-McArdle.

Four modes let you calculate with each formula individually or compare all three side by side. Enter your age, gender, height, and weight to get your BMR estimate. Pairs well with our TDEE and Calorie calculators.

Age (years)

Weight (kg)

Height (cm)

Your calculations will appear here

How to Use the BMR Calculator

Pick a formula: Mifflin-St Jeor, Harris-Benedict, Katch-McArdle, or Compare All to see them side by side.
Enter your age in years, choose metric (kilograms and centimetres) or imperial (pounds, feet and inches), and enter your weight and height. The imperial fields are converted for you (1 lb is 0.4536 kg and 1 inch is 2.54 cm). Choose male or female, the two options the equations are defined for.
Katch-McArdle needs your body fat percentage. Enter it in the optional field and the result includes your lean body mass.
The result is in kilocalories per day. To turn it into a daily calorie target, multiply by an activity factor or use the TDEE Calculator. These results are estimates and not medical advice.

Formula and Theory

Basal metabolic rate (BMR) is the energy your body uses at complete rest, to keep breathing, circulating blood and maintaining temperature. It makes up the largest share of daily energy use for most adults. The numbers are estimates from population equations, so individual values vary.

Mifflin-St Jeor (1990) is the equation most often recommended today: BMR = 10 x weight (kg) + 6.25 x height (cm) - 5 x age + 5 for men, or - 161 for women. The revised Harris-Benedict equation (1984) uses different coefficients: men 88.362 + 13.397 x weight + 4.799 x height - 5.677 x age; women 447.593 + 9.247 x weight + 3.098 x height - 4.330 x age.

Katch-McArdle bases the estimate on lean body mass instead of total weight: BMR = 370 + 21.6 x lean body mass (kg), where lean body mass = weight x (1 - body fat fraction). It can suit people with an unusual body composition, but it needs a body fat figure that is itself an estimate.

These formulas give an estimate. They do not measure metabolism, and medical conditions, medicines, pregnancy and age extremes all change real energy needs. They are not medical advice; talk to a doctor or registered dietitian for personal guidance.

Worked Examples

Example 1: Mifflin-St Jeor for a woman

Problem: A 30-year-old woman weighs 70 kg and is 175 cm tall.

Solution: 10 x 70 = 700. 6.25 x 175 = 1,093.75. 5 x 30 = 150. Subtotal = 700 + 1,093.75 - 150 = 1,643.75. For women subtract 161: 1,643.75 - 161 = 1,482.75.

Answer: About 1,483 kcal/day

Example 2: A smaller frame

Problem: A 45-year-old woman weighs 60 kg and is 160 cm tall.

Solution: 10 x 60 = 600. 6.25 x 160 = 1,000. 5 x 45 = 225. BMR = 600 + 1,000 - 225 - 161 = 1,214.

Answer: 1,214 kcal/day

Example 3: Harris-Benedict for the same man

Problem: Use the revised Harris-Benedict equation for a 30-year-old man, 70 kg, 175 cm.

Solution: 88.362 + 13.397 x 70 + 4.799 x 175 - 5.677 x 30 = 88.362 + 937.79 + 839.825 - 170.31 = 1,695.667.

Answer: About 1,696 kcal/day (57 kcal higher than Mifflin-St Jeor)

Example 4: Katch-McArdle with body fat

Problem: A person weighs 70 kg and has 20% body fat.

Solution: Lean body mass = 70 x (1 - 0.20) = 56 kg. BMR = 370 + 21.6 x 56 = 370 + 1,209.6 = 1,579.6.

Answer: About 1,580 kcal/day, lean body mass 56 kg

Frequently Asked Questions

What is BMR?

Basal metabolic rate is the number of calories your body burns at rest in a day, without any activity. It is the starting point for estimating how much you need to eat.

Which BMR formula is most accurate?

For most people Mifflin-St Jeor is the closest of the common equations. Katch-McArdle can be better when you know your body fat percentage. Use Compare All to see how far apart they are for you.

What is the difference between BMR and TDEE?

BMR is energy at rest. TDEE (total daily energy expenditure) adds the energy used for movement, exercise and digestion, found by multiplying BMR by an activity factor from 1.2 to 1.9.

Why do I get different results from different formulas?

They were fitted to different groups of people and use different inputs, so they differ by tens of kilocalories for most adults. Treat the result as a range, not an exact figure.

Does muscle change my BMR?

Lean tissue uses more energy at rest than fat, which is why the Katch-McArdle formula is built on lean body mass. The difference per kilogram is modest.

Can I use this to decide how much to eat?

It gives a starting estimate only. It is not medical advice, and anyone with a health condition, who is pregnant, or planning a large change in weight should speak to a doctor or registered dietitian.