Health
Daily calorie calculator
Estimates how much energy your body uses at rest and across a typical day, using the equation most clinicians reach for first.
The equation
This uses Mifflin-St Jeor, published in 1990 and since found in review studies to be more accurate for most adults than the older Harris-Benedict equation it replaced.
BMR (female) = 10w + 6.25h − 5a − 161
w = weight in kg, h = height in cm, a = age in years
TDEE = BMR × activity multiplier
BMR and TDEE are different numbers
Basal metabolic rate is what your body would use lying still all day — keeping your heart beating, your temperature stable and your organs running. It's the floor, not a target, and for most adults it accounts for around 60 to 70 per cent of total daily energy use.
Total daily energy expenditure adds everything else: digesting food, walking to the kitchen, fidgeting, and deliberate exercise. The activity multiplier is a crude way of capturing all of that in one number, which is where most of the imprecision in the result comes from.
How accurate is the estimate?
Mifflin-St Jeor lands within 10 per cent of measured resting expenditure for roughly four out of five people. That means an estimate of 1,600 could reasonably be 1,450 or 1,750 — and the activity multiplier widens the range further, because two people who both describe themselves as "moderately active" can differ substantially in how much they actually move.
Two known limitations are worth stating plainly. The equation uses total body weight, so it underestimates needs for very muscular people and overestimates for people carrying a lot of fat mass, since fat tissue burns less energy at rest. And it was developed on adults, so it doesn't apply to children or adolescents, or during pregnancy or breastfeeding.
Treat the figure as a starting reference point rather than a prescription. If you're planning to change what you eat for a health reason, a doctor or registered dietitian can account for the things an equation can't see — medication, thyroid function, medical history and your actual eating patterns.
Common questions
Which activity level should I pick?
Most people overestimate. If you have a desk job and train three times a week, "lightly active" is usually closer than "moderately active" — the multiplier is meant to cover your whole week, not the intensity of your best session.
What are the macros on the tape?
A common general-purpose split of 40 per cent carbohydrate, 30 per cent protein and 30 per cent fat, converted to grams at 4 kcal per gram for carbohydrate and protein and 9 kcal per gram for fat. It's one reasonable distribution among many, not a recommendation for your situation.
Why does the number fall as I get older?
The equation subtracts 5 calories per year of age, reflecting the gradual loss of lean tissue that typically accompanies ageing. Maintaining muscle through resistance training slows that decline, though the equation can't detect it because it doesn't measure body composition.