Why use this calculator
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 parts that matter.
Basal metabolic rate is what your body spends simply keeping you alive, usually the large majority of the total, and it barely moves from day to day. The rest is activity, the part you influence and the part most likely to be overstated. Seeing them apart explains why exercise alone rarely changes weight much.
It also runs a second published equation alongside the first and shows the gap between them, so the uncertainty is visible on the page instead of hidden behind a single confident-looking figure.
How to use it
- Choose your unit system first, since the weight and height fields change with it.
- Enter weight measured in the morning before eating, because food and fluid shift the scale by one to two kilograms across a day.
- Enter height measured against a wall without shoes, as adults lose height slowly from their thirties and remembered figures are often wrong. Enter your age in whole years. Choose your sex, which sets the equation constants.
- Choose the activity level that describes a typical week, and take the lower option if you sit between two.
- Finally choose the equation: Mifflin-St Jeor suits most people, revised Harris-Benedict is the older standard, and Katch-McArdle is the best choice if you know your body fat percentage, because it works from lean mass instead of total weight.
What each result means
- BMR (Basal Metabolic Rate)
- The energy your body uses at complete rest to run organs, hold temperature and repair tissue. Not a figure to eat below without supervision.
- TDEE (Maintenance Calories)
- Resting rate multiplied by your activity factor: roughly the intake that holds your weight steady on a weekly average.
- Activity Multiplier
- The factor applied to your resting rate. It carries more uncertainty than the equation itself, so choose it conservatively.
- Calories From Activity
- Everything you burn above resting: deliberate exercise, incidental movement, fidgeting and the energy cost of digesting food.
- Weight Loss Target (500 kcal deficit)
- A moderate deficit predicting about half a kilogram or one pound a week, slow enough to preserve muscle for most people.
- Weight Gain Target (500 kcal surplus)
- A moderate surplus for gaining. With resistance training a larger share of the gain is lean tissue rather than fat.
- Cross-check From Another Equation
- The resting rate a second published equation gives for the same inputs, and the percentage gap, so the real uncertainty is visible.
The formula
Mifflin-St Jeor: BMR equals 10 x weight in kilograms plus 6.25 x height in centimetres minus 5 x age in years, plus 5 for men or minus 161 for women. Revised Harris-Benedict for men: BMR equals 88.362 plus 13.397 x weight in kilograms plus 4.799 x height in centimetres minus 5.677 x age; for women: 447.593 plus 9.247 x weight plus 3.098 x height minus 4.330 x age. Katch-McArdle: BMR equals 370 plus 21.6 x lean body mass in kilograms, where lean mass is weight x (1 minus body fat percentage divided by 100). Total daily energy expenditure is BMR multiplied by an activity factor of 1.2 sedentary, 1.375 lightly active, 1.55 moderately active, 1.725 very active or 1.9 extra active. All figures are kilocalories per day.
How this number is used in practice
The most useful thing this number does is reset expectations about exercise. Deliberate training is often only five to fifteen per cent of total expenditure, which is why thirty minutes of moderate activity burns roughly what sits in a single muffin. Exercise earns its place through cardiovascular health, strength, mood, sleep and appetite regulation, not through calorie arithmetic, and treating it as the main weight lever is why so many people train hard for months and see nothing change on the scale.
The larger and more variable component is everything else you do while awake, which quietly falls when you eat less.
The equation also stops being right within a few months of any real change. A lighter body needs less energy simply to exist, unconscious daily movement drops during a deficit, and logging accuracy drifts as portion sizes creep back up. Recalculating every five to ten kilograms and adjusting on your actual weight trend rather than on the formula is what makes a plan work across a year.
Your own two-week trend is a better estimate of your expenditure than any published equation. Anyone who is pregnant or breastfeeding, under 18, or managing a thyroid condition, diabetes or an eating disorder should treat these figures as background reading only and get individual advice, because the population equations were not built for those situations.
Worked examples
30 year old male, 170 lb, 70 in, moderately active, Mifflin-St Jeor
Resting rate 1,737 kcal and total expenditure 2,693 kcal a day, with 956 kcal of that coming from activity.
40 year old female, 68 kg, 165 cm, lightly active, Mifflin-St Jeor
Resting rate 1,350 kcal and total expenditure 1,857 kcal a day, so a moderate deficit lands near 1,357 kcal.
25 year old male, 90 kg, 180 cm, extra active, Mifflin-St Jeor
Resting rate 1,905 kcal and total expenditure 3,620 kcal a day: the activity multiplier adds more than three moderate deficits.
When people use it
- Setting a starting calorie target before beginning a cut or a bulk
- Understanding how much of your daily burn is resting rather than exercise
- Checking whether a diet plan or app has set an unrealistically low intake
- Recalculating after a change in training volume, a new job or 5 kg of weight change
- Comparing what two published equations say about the same body, to see the error bar
Tips
- Choose the activity level one step below your instinct. Self-rated activity is the single largest source of error in this calculation.
- Do not set a target below your basal metabolic rate without supervision. It makes adequate protein and micronutrients very hard to hit.
- Use Katch-McArdle if you have a reliable body fat figure. Working from lean mass beats working from total weight, especially at the extremes.
- Recalculate every 5 to 10 kg of weight change, because a lighter body burns less at rest and through movement.
- Track weekly average weight for two to three weeks and use that trend as your real expenditure, rather than trusting the equation indefinitely.
- Count drinks. Alcohol supplies 7 kcal per gram and is missing from most people's mental arithmetic.
- Add steps before you add cardio. Incidental movement is larger and easier to sustain than structured training for most people.
What it assumes, and where it stops being accurate
- Predictive equations estimate measured resting metabolic rate within about 10 per cent for most adults, and are less reliable for very muscular, very lean or severely obese people.
- Activity factors are broad bands rather than measurements. Two people at the same band can genuinely differ by 400 kcal a day.
- The Katch-McArdle option is only as good as the body fat percentage you feed it, and tape or caliper estimates carry several percentage points of error.
- The 500 kcal deficit and surplus figures use the rule of 3,500 kcal per pound of fat, which overstates long-run loss because expenditure falls as weight falls.
- It assumes no pregnancy, breastfeeding, fever, major injury, or medication that alters metabolic rate, all of which change requirements substantially.
- It is not valid for children and adolescents, whose needs are driven by growth and are assessed against age and sex specific references.
Terms used on this page
- Basal metabolic rate
- Energy used at complete rest in a fasted, thermally neutral state to maintain vital function.
- Total daily energy expenditure
- Resting metabolic rate plus activity, incidental movement and the thermic effect of food.
- Thermic effect of food
- Energy spent digesting and absorbing meals, roughly 10 per cent of intake and highest for protein.
- Lean body mass
- Everything that is not fat: muscle, bone, organs and water. The driver in the Katch-McArdle equation.
- Activity factor
- The multiplier applied to resting rate, from 1.2 for sedentary to 1.9 for extra active.
Questions people ask
- What is the difference between BMR and TDEE?
- Basal metabolic rate is what you burn at complete rest, keeping organs running and temperature stable, and it is usually 60 to 70 per cent of the total. Total daily energy expenditure adds everything else: deliberate exercise, incidental movement and the energy cost of digesting food. TDEE is the figure you compare your eating against.
- Which equation should I use?
- Mifflin-St Jeor is the default because it predicts measured resting rate more closely than the older Harris-Benedict formula across most adults. Use Katch-McArdle instead if you have a trustworthy body fat percentage, since it works from lean mass and handles very muscular or very lean bodies better than weight-based equations do.
- How accurate is a TDEE calculator?
- Expect roughly plus or minus 10 per cent from the equation itself, and more once the activity multiplier is applied. On a 2,700 calorie estimate that is a range of several hundred calories. It is a starting point to test, not a measurement. Your own weight trend across two to three weeks is a better estimate than any formula.
- Why does my TDEE drop as I lose weight?
- A smaller body costs less to run and less to move, so both resting rate and the energy cost of activity fall. Unconscious movement also declines during a deficit. Together this is why a target that worked at the start of a diet stalls a few months in, and why recalculating every 5 to 10 kilograms matters.
- Should I eat back the calories I burn in exercise?
- Not if you chose an activity level that already includes your training, because you would be counting it twice. That double counting is the most common mistake people make with these tools. Pick sedentary and log workouts separately, or pick an honest activity level and ignore what your watch reports.
- Are fitness tracker calorie numbers reliable?
- Wrist-worn trackers estimate energy expenditure from heart rate and movement, and independent testing consistently finds errors of 20 to 30 per cent, usually overstating the burn. They are useful for tracking relative effort and trends over time, but poor as an input to a calorie budget.
Use this with
TDEE Calculator answers one part of the question. These pick up where it stops: BMR Calculator, Macronutrient Calculator, Calorie Calculator and Calories Burned Calculator.
Where these figures come from
This calculation is jurisdiction-neutral arithmetic. No country-specific rules are applied.
- NIH NIDDK: weight management. Energy balance and expected rates of weight change
- World Health Organization: obesity and overweight. Population energy balance guidance
- NHS: healthy weight. Daily calorie reference intakes and safe rates of loss
TDEE 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.