Why use this calculator
Almost every nutrition decision starts from one number: how much energy you actually use in a day. Without it a calorie target is a guess, and most people guess badly in both directions, underestimating what they eat and overestimating what they burn. This calculator separates the two components that matter.
Basal metabolic rate is what your body spends keeping you alive, the majority of the total, and it barely moves day to day. Total daily energy expenditure adds activity, which is the part you influence and the part most likely to be overstated. Seeing them apart makes it obvious why exercise alone rarely changes weight much.
How to use it
- Pick your units, then enter age, sex, weight and height as accurately as you can, since the equation is sensitive to all four.
- Weigh yourself first thing in the morning under consistent conditions.
- The activity multiplier is where most of the error enters: people consistently rate themselves a level above where they actually sit, so if you are between two options choose the lower one.
- Sedentary means a desk job with little deliberate movement, and moderate means genuine structured exercise three to five days a week rather than an intention to start.
- Treat the result as a two-week hypothesis rather than a fixed figure.
What each result means
- BMR (Calories/day)
- Energy used at complete rest to run organs, maintain temperature and repair tissue. Typically 60 to 70 per cent of your total, and not a figure to eat below.
- Burned by daily activity
- Maintenance minus BMR: the energy your chosen activity level adds on top of resting needs. It is the part of the total you can change most by moving more.
- TDEE (Maintenance Calories)
- Total daily energy expenditure including activity. Roughly what you need to eat to hold your current weight.
- Weight Loss (500 cal deficit)
- A moderate deficit predicting about half a kilogram a week. Sustainable for most people and slow enough to preserve muscle.
- Weight Gain (500 cal surplus)
- A moderate surplus for gaining weight. Paired with resistance training, more of the gain is muscle rather than fat.
The formula
The Mifflin-St Jeor equation is used because it predicts measured expenditure more accurately than the older Harris-Benedict formula.
For men:
BMR = 10 x weight in kg + 6.25 x height in cm - 5 x age + 5
For women the final term is minus 161 instead of plus 5. Total daily energy expenditure multiplies BMR by an activity factor: 1.2 sedentary, 1.375 lightly active, 1.55 moderately active, 1.725 very active and 1.9 extra active. A 500 calorie daily deficit predicts roughly a pound of loss a week, since a pound of body fat stores about 3,500 calories.
How this number is used in practice
The most useful thing this number does is reset expectations about exercise. Deliberate exercise is often only five to fifteen per cent of total expenditure, which is why thirty minutes of moderate activity burns roughly what is in a muffin. Exercise earns its place through cardiovascular health, strength, mood and appetite regulation rather than through calorie arithmetic, and treating it as the primary weight lever is why so many people train hard and see nothing change.
The equation is a starting point that stops being right within a few months. A lighter body needs less energy simply to exist, unconscious daily movement falls during a deficit, and logging accuracy drifts as portions creep up. Recalculating every five to ten kilograms and adjusting on the basis of your actual weight trend, rather than the formula, is what makes the process work over a year. Your own two-week trend is a better estimate of your expenditure than any equation.
Worked examples
30 year old male, 5 ft 10 in, 176 lb, moderately active
BMR of 1,737 calories and a TDEE of 2,693, giving a loss target of 2,193 and a gain target of 3,193.
40 year old female, 165 cm, 68 kg, lightly active
BMR near 1,367 calories and a TDEE around 1,880, so a moderate deficit lands close to 1,400.
25 year old male, 180 cm, 90 kg, very active
BMR near 1,930 calories and a TDEE around 3,330. The activity multiplier adds more than the entire deficit.
When people use it
- Setting a starting calorie target for weight loss or gain
- Understanding how much of your daily burn is resting versus activity
- Checking whether a diet plan sets an unrealistically low intake
- Adjusting intake after a change in training volume or a new job
- Explaining why exercise alone rarely moves weight much
Tips
- Choose the activity level one step below your instinct. Self-rated activity is consistently overstated.
- Do not eat below your BMR without supervision; it makes adequate protein and micronutrients hard to hit.
- Recalculate every 5 to 10 kg of weight change, because a lighter body burns less at rest.
- Aim for 1.6 to 2.2 g of protein per kg of body weight in a deficit to preserve muscle.
- Judge progress on weekly averages, not single weigh-ins. Daily swings of 1 to 2 kg are water and food.
- If two weeks at the target produce no change, adjust by 100 to 200 calories rather than assuming the formula failed.
What it assumes, and where it stops being accurate
- Mifflin-St Jeor predicts measured expenditure within roughly 10 per cent for most adults, and less well at the extremes of body composition.
- Body composition is not an input, so the equation underestimates for very muscular people and overestimates for the opposite.
- Activity multipliers are broad bands and are the largest single source of error in the result.
- The 3,500 calories per pound rule is an approximation that overstates loss as weight falls.
- Medical conditions, medication and thyroid function shift actual expenditure and are not modelled.
Terms used on this page
- Basal metabolic rate
- Energy used at complete rest to maintain essential body functions.
- Total daily energy expenditure
- BMR plus digestion, deliberate exercise and everyday movement.
- Mifflin-St Jeor equation
- The current standard equation for estimating resting metabolic rate from height, weight, age and sex.
- Thermic effect of food
- The energy used digesting and absorbing food, roughly 10 per cent of intake.
Questions people ask
- What is the difference between BMR and TDEE?
- BMR is what your body uses at complete rest, breathing, circulation, temperature, tissue repair, and is usually 60 to 70 per cent of the total. TDEE adds the thermic effect of food, deliberate exercise and everyday movement on top. TDEE is the figure to compare your intake against; BMR is a floor you should not eat below.
- How accurate is this calculator?
- The Mifflin-St Jeor equation predicts measured resting expenditure within about 10 per cent for most adults, which on a 1,700 calorie BMR is 170 calories either way. The activity multiplier adds more uncertainty than the equation itself. Use the output as a two-week starting point and let your actual weight trend correct it.
- Which activity level should I choose?
- Sedentary means a desk job and little deliberate movement. Lightly active means one to three sessions a week. Moderately active means three to five genuine sessions. Very active means six or seven, or physical work. If you are between two, pick the lower one. Overstating activity is the most common reason a calorie target fails.
- Why am I not losing weight at my deficit?
- Three usual causes. A lighter body burns less, so the deficit narrows as you lose. Unconscious daily movement drops during a deficit. And logging accuracy drifts as portions grow and small bites go uncounted. Audit a few days of intake carefully and recalculate at your current weight before concluding your metabolism is unusual.
- Can I eat below my BMR to lose faster?
- It is rarely appropriate without supervision. Very low intakes make protein and micronutrient targets hard to reach, cost more muscle, and are difficult to sustain, which is why they so often end in regain. A moderate deficit held for longer produces better outcomes than an aggressive one abandoned in three weeks.
Use this with
BMR Calculator answers one part of the question. These pick up where it stops: Calorie Calculator, TDEE Calculator, Macronutrient Calculator and BMI Calculator.
Where these figures come from
This calculation is jurisdiction-neutral arithmetic. No country-specific rules are applied.
- Eat For Health: Australian Dietary Guidelines. Energy and nutrient reference values
- Heart Foundation: physical activity and exercise. Activity guidance for adults
BMR Calculator produces an estimate for general information. It is not financial, tax, medical, legal or engineering advice. read the full disclaimer. Spotted a wrong number? Report it and it gets fixed. The form picks up this calculator and the inputs you used.