Calculate your Basal Metabolic Rate (BMR) — the number of calories your body needs at rest — using three different formulas. Results shown in both kcal and kJ (as used on Australian food labels).
BMR (Basal Metabolic Rate) is the number of calories your body burns at complete rest just to stay alive — powering your heart, lungs, brain and cell repair. It is the largest part of your daily calorie burn, usually 60–70%. BMR is calculated from your age, sex, height and weight, and forms the base for working out your total daily calorie needs (TDEE).
| Formula | BMR (kcal) | BMR (kJ) | TDEE (kcal) |
|---|
| Activity Level | kcal/day | kJ/day |
|---|
There are three widely used BMR equations. Mifflin-St Jeor is the modern default; Katch-McArdle is best if you know your body fat percentage.
| Formula | Best For | Needs Body Fat %? |
|---|---|---|
| Mifflin-St Jeor | Most people — the modern standard | No |
| Harris-Benedict | Older formula, still widely referenced | No |
| Katch-McArdle | Lean or muscular people who know their body fat | Yes |
BMR and RMR (Resting Metabolic Rate) are often used interchangeably, but they are measured slightly differently.
| Feature | BMR | RMR |
|---|---|---|
| Measurement conditions | Strict — after sleep, fasted, fully rested | Relaxed — normal resting conditions |
| Typical value | Slightly lower | Slightly higher (~10%) |
| Everyday use | Used in most calculators | Often used interchangeably with BMR |
You can modestly raise your BMR over time, mainly by building muscle, since muscle burns more energy at rest than fat. Evidence-based ways to support a healthy metabolism include:
Be sceptical of foods, supplements or "tricks" that claim to dramatically boost metabolism — the real drivers are muscle mass, activity and body size.
Your Basal Metabolic Rate (BMR) is the energy your body needs to maintain vital functions at complete rest — breathing, circulation, cell production, and temperature regulation. It accounts for 60–75% of total daily energy expenditure for most people.
The Mifflin-St Jeor equation (1990) is generally considered the most accurate for most people and is recommended by the Academy of Nutrition and Dietetics. The Katch-McArdle formula is most accurate for lean individuals who know their body fat percentage, as it accounts for lean body mass.
Australian food labels display energy in kilojoules (kJ). The conversion is: 1 kcal = 4.184 kJ. The average Australian adult daily energy intake is approximately 8,700 kJ (2,080 kcal) for men and 7,100 kJ (1,697 kcal) for women, though individual requirements vary widely.
Age (BMR decreases ~2% per decade after 20), muscle mass, body size, hormones (thyroid), temperature, diet composition, and genetics all influence BMR. Building muscle through resistance training is one of the most effective ways to increase BMR long-term.
The NHMRC publishes Estimated Energy Requirements (EERs) for Australians by age, sex, and physical activity level. These are used as reference values for dietary planning and are based on doubly-labelled water studies.
BMR (Basal Metabolic Rate) is the number of calories your body burns in a state of complete rest — the minimum energy needed to maintain basic life functions including breathing, circulation, temperature regulation, and organ function. It represents approximately 60-75% of total daily calorie expenditure for most people.
BMR is not the same as your total daily calorie needs — it assumes you are lying completely still for 24 hours. Your actual calorie needs (TDEE — Total Daily Energy Expenditure) are higher, calculated by multiplying BMR by an activity factor.
Example: 35-year-old man, 80kg, 178cm: BMR = (10×80) + (6.25×178) − (5×35) + 5 = 800 + 1,112.5 − 175 + 5 = 1,742 calories/day
| Measure | Definition | Typical % |
|---|---|---|
| BMR | Calories at complete rest | 60-75% of TDEE |
| TEF (Thermic Effect of Food) | Calories used digesting food | ~10% of TDEE |
| NEAT (Non-Exercise Activity) | Fidgeting, walking, standing | 15-30% of TDEE |
| EAT (Exercise Activity) | Deliberate exercise | 5-10% of TDEE |
| TDEE | Total Daily Energy Expenditure | 100% |
What is BMR in simple terms?
BMR (Basal Metabolic Rate) is the number of calories your body burns in 24 hours if you did nothing but lie completely still. It represents your body's minimum energy requirement to sustain breathing, heartbeat, temperature regulation, and organ function. BMR accounts for approximately 60-75% of most people's total daily calorie burn.
Which BMR formula is most accurate?
The Mifflin-St Jeor equation (1990) is consistently validated as the most accurate formula for predicting BMR in most healthy, non-obese adults. The Harris-Benedict equation (revised 1984) overestimates BMR by approximately 5%. For individuals who know their body fat percentage, the Katch-McArdle formula is more accurate as it uses lean body mass directly.
Does BMR change with age?
Yes. BMR declines approximately 1-2% per decade after age 20. The primary reason is loss of muscle mass (sarcopenia) — muscle tissue burns significantly more calories at rest than fat tissue. Resistance training is the most effective strategy to preserve muscle mass and limit the age-related BMR decline.
Can I increase my BMR?
The most effective way to increase BMR long-term is resistance training to build and maintain muscle mass. Short-term, intense exercise temporarily elevates metabolic rate through EPOC (excess post-exercise oxygen consumption). Severely restricting calories causes adaptive thermogenesis — BMR decreases as the body conserves energy, which is one reason very low calorie diets are difficult to sustain.
How do I use BMR to calculate my calorie needs?
Multiply your BMR by your activity factor: Sedentary (desk job, little exercise): BMR × 1.2. Lightly active (1-3 days/week exercise): BMR × 1.375. Moderately active (3-5 days): BMR × 1.55. Very active (6-7 days hard exercise): BMR × 1.725. Extra active (physical job + hard exercise): BMR × 1.9. The result is your TDEE — your estimated total daily calorie need.
How do I calculate my BMR?
Use the Mifflin-St Jeor formula with your age, sex, height and weight, or simply enter them in the calculator above. For women: (10×kg)+(6.25×cm)−(5×age)−161; for men the same but +5 instead of −161. The result is the calories you burn at rest.
What is the difference between BMR and TDEE?
BMR is the calories you burn at complete rest. TDEE is your whole-day burn — BMR plus movement, exercise and digestion. You calculate TDEE by multiplying BMR by an activity factor. BMR is always the smaller, baseline number.
Why is BMR different for men and women?
On average men have more muscle and less body fat than women of the same size, and muscle burns more energy at rest. That is why the formulas add calories for men and subtract for women, giving men a higher BMR at the same height and weight.
Does BMR change with age?
Yes. BMR gradually falls with age as muscle mass declines and cells become less active, which is why the formulas subtract calories for each year. Staying active and maintaining muscle through strength training helps slow this decline.
Can I increase my BMR?
Modestly, yes — mainly by building muscle through strength training, since muscle burns more at rest than fat. Enough protein, good sleep and regular activity also help. Be wary of foods or supplements promising a big metabolism boost; the real drivers are muscle and body size.
How accurate is a BMR calculator?
BMR formulas give a good estimate for most people but can be off for those with very high or low muscle mass, certain medical conditions, or unusual body composition. Use the result as a reliable starting point rather than an exact figure.