Your body burns energy at rest - the basal metabolic rate - and more on top depending on how much you move. This estimates both, then gives calorie targets for gaining or losing weight at various rates, and splits any target into protein, carbohydrate and fat.
Basal metabolic rate is what you would burn lying still all day - typically 60 to 70% of your total. Total daily energy expenditure adds movement, exercise and the energy cost of digesting food. TDEE is the number to eat around. Eating at BMR is a severe deficit, not maintenance.
Height, weight and age are measured; activity is guessed from a five-point scale. Most people overestimate. If your weight is not moving the way the calculator predicts, the multiplier is the first thing to revise, not the formula. A good approach: eat at the estimate for two or three weeks, weigh yourself regularly, and adjust from what actually happened.
Mifflin-St Jeor is the most accurate for the general population and is the default. Harris-Benedict is older and reads roughly 5% high. Katch-McArdle uses lean mass instead of sex and age, so it is the better choice if you know your body fat percentage and are unusually lean or muscular - which is exactly where the weight-based formulas struggle.
About 500 calories a day below maintenance loses roughly half a kilogram a week. Larger deficits take more muscle with the fat, are harder to sustain, and tend to end in rebound. Very low intakes belong under medical supervision, not a web calculator.
BMR is what you would burn lying still all day keeping your organs running - typically 60 to 70% of the total. TDEE adds movement, exercise and the energy cost of digesting food. TDEE is the number to eat around; BMR is only the starting point for it.
Mifflin-St Jeor by default, which is the most accurate of the prediction equations for the general population. Harris-Benedict is offered for comparison and tends to read about 5% high. Katch-McArdle uses lean body mass instead of sex and age, and is better if you know your body fat percentage and are unusually lean or muscular.
For an individual, within roughly 10% either way. Metabolic rate varies between people of identical size, and the activity multipliers are coarse. Treat the figure as a starting point: eat at it for two or three weeks, track your weight, and adjust from what actually happens rather than from the formula.
Around 500 calories a day, which is roughly half a kilogram or a pound a week. Larger deficits lose more muscle alongside fat, are harder to sustain, and tend to end in rebound. Very low intakes should only be done under medical supervision.
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