About the BMR calculator
Basal metabolic rate (BMR) is the energy your body uses at complete rest to keep you alive: breathing, circulation, temperature control and cell repair. This calculator estimates BMR with three published equations so you can compare them.
BMR is the foundation for working out how many calories you burn in a day, but it is only an estimate. Two people with the same numbers can differ by a couple of hundred calories.
Who should use the BMR calculator
- Anyone starting to plan food intake and wanting a baseline energy figure.
- People who know their body fat percentage and want a lean-mass-based estimate.
- Students comparing how different equations behave.
How to use the BMR calculator: what each input means
- Sex used in the formula
- The equations were fitted separately for males and females, so one of the two must be chosen.
- Age, height, weight
- Entered in metric, US or UK units.
- Equation
- Mifflin-St Jeor, revised Harris-Benedict, or Katch-McArdle (which also needs body fat percentage).
- Energy unit
- Calories (kcal) or kilojoules (kJ). 1 kcal = 4.184 kJ.
How the BMR calculator works: method and formula
Mifflin-St Jeor (1990) and the revised Harris-Benedict (1984) equations estimate BMR from weight, height, age and sex. Katch-McArdle uses lean body mass, so it needs a body fat percentage and tends to be more useful for people who are very lean or very muscular.
The calculator shows all three results so you can see the spread rather than relying on a single number.
- Mifflin-St Jeor
- BMR = 10 × kg + 6.25 × cm − 5 × age + 5 (male) or − 161 (female)
- Revised Harris-Benedict (male)
- BMR = 88.362 + 13.397 × kg + 4.799 × cm − 5.677 × age
- Revised Harris-Benedict (female)
- BMR = 447.593 + 9.247 × kg + 3.098 × cm − 4.330 × age
- Katch-McArdle
- BMR = 370 + 21.6 × lean body mass (kg)
How to read your BMR calculator result
Treat the result as a baseline, not a target. Total daily energy use is higher once you add daily movement and exercise, which the calorie calculator handles. Equations differ by tens to a couple of hundred calories, so if they disagree, you are seeing the real uncertainty.
Do not eat below your BMR for long periods without medical supervision. BMR is not a recommended intake.
BMR Calculator worked example
A 30-year-old woman, 175 cm tall, weighing 70 kg (with a body fat of 25% for the Katch-McArdle line).
- Mifflin-St Jeor: 10 × 70 + 6.25 × 175 − 5 × 30 − 161 = 1,483 kcal/day.
- Revised Harris-Benedict: 447.593 + 9.247 × 70 + 3.098 × 175 − 4.330 × 30 = 1,507 kcal/day.
- Katch-McArdle: lean mass = 70 × 0.75 = 52.5 kg, so 370 + 21.6 × 52.5 = 1,504 kcal/day.
Estimates range from about 1,483 to 1,507 kcal per day.
Practical uses of the BMR calculator
- Setting a starting point for a nutrition plan with a professional.
- Understanding why two people of the same weight need different amounts of energy.
- Comparing equations when your body fat percentage is known.
Assumptions and limitations of this calculator
- All three are estimates fitted to groups of people; individual metabolism varies.
- Equations were developed for adults and may be less reliable for older adults, very high or very low body weights, and athletes.
- The sex field refers to the dataset the formulas were fitted on and is not a statement about identity. Pregnancy, illness and medication can also change energy needs.
This calculator is for general information and education only. It is not medical advice, a diagnosis or a treatment plan. Results are estimates based on population formulas and cannot account for your individual health. If you have a medical condition, are pregnant, are under 18, or are planning a major change to your diet or exercise, speak to a doctor or registered dietitian first.