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Health & Fitness

BMR Calculator

Estimate your basal metabolic rate (the calories your body burns at rest) with the Mifflin-St Jeor, revised Harris-Benedict or Katch-McArdle formula, plus daily calories for five activity levels.

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Height
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Results are estimates from predictive equations, not medical advice.

How to use the BMR calculator

Choose US or Metric units and enter your age (15 to 80), sex, weight and height. Then pick a formula. Mifflin-St Jeor is selected by default. If you know your body fat percentage, you can choose Katch-McArdle, and a body fat field appears. Press Calculate to see your BMR in kcal per day and a table with your estimated daily calorie needs at five activity levels.

What BMR means

Basal metabolic rate is the energy your body uses at complete rest just to stay alive: breathing, circulating blood, keeping its temperature and repairing cells. For most people it makes up the largest share of the calories they burn each day, even when they exercise regularly.

The formulas

Mifflin-St Jeor (1990)

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

Revised Harris-Benedict (Roza and Shizgal, 1984)

  • Men: 88.362 + 13.397 × weight + 4.799 × height − 5.677 × age
  • Women: 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 is your weight minus your fat mass. This formula does not use age or sex, so it can suit lean, muscular people better, but it is only as accurate as your body fat estimate.

Worked example

A 30-year-old man who weighs 80 kg (about 176 lb) and is 180 cm (about 5 ft 11 in) tall:

  • Mifflin-St Jeor: 800 + 1,125 − 150 + 5 = 1,780 kcal/day
  • Revised Harris-Benedict: 88.362 + 1,071.76 + 863.82 − 170.31 ≈ 1,854 kcal/day
  • Katch-McArdle with 20% body fat: lean mass 64 kg, so 370 + 21.6 × 64 ≈ 1,752 kcal/day

With a sedentary lifestyle (factor 1.2), the Mifflin-St Jeor result becomes about 2,136 kcal per day.

Calories by activity level

The table multiplies your BMR by a standard activity factor: sedentary 1.2, light 1.375, moderate 1.55, very active 1.725 and extra active 1.9. The result is an estimate of your total daily energy expenditure, the amount you would eat to keep your weight stable.

Good to know

  • Every formula gives an estimate. Measured BMR can differ from the prediction by 10% or more for some people.
  • Muscle burns more energy than fat, so two people with the same weight can have quite different BMRs.
  • BMR tends to fall slightly with age and during weight loss.
  • The results are not medical advice and do not apply during pregnancy or breastfeeding. Speak to a doctor or registered dietitian if you have a health condition.

Frequently asked questions

Which BMR formula should I use?

For most adults Mifflin-St Jeor is a good default because comparison studies have found it to be among the more accurate predictive equations. Katch-McArdle can be a better fit if you are lean or very muscular and have a reliable body fat measurement. The revised Harris-Benedict formula is included because it is still widely used and lets you compare results.

What is the difference between BMR and TDEE?

BMR is the energy you burn at complete rest. TDEE, or total daily energy expenditure, adds the energy used for daily activity and exercise. The activity table in this calculator shows estimated TDEE values for five activity levels.

Why does the body fat field only appear for Katch-McArdle?

Katch-McArdle calculates BMR from lean body mass, which needs your body fat percentage. Mifflin-St Jeor and Harris-Benedict use age, sex, height and weight instead, so they do not need it.

Can I eat less than my BMR to lose weight faster?

Eating below your BMR for long periods is generally not recommended without medical supervision. It makes it harder to get enough nutrients and may lead to muscle loss. A moderate deficit below your TDEE is a more common approach.