Calorie calculator
Estimate the calories you burn each day using the Mifflin-St Jeor equation, with targets for maintaining, losing or gaining weight.
Daily calories to maintain weight
2,267 kcal
Your resting metabolic rate is about 1,649 kcal a day before any activity.
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The equation
This calculator uses Mifflin-St Jeor, published in 1990 and since found by the Academy of Nutrition and Dietetics to be the most reliable predictive equation for resting energy expenditure in both normal-weight and obese adults.
Men: BMR = (10 × kg) + (6.25 × cm) − (5 × age) + 5
Women: BMR = (10 × kg) + (6.25 × cm) − (5 × age) − 161Total daily energy expenditure then applies an activity multiplier:
TDEE = BMR × activity factor| Activity level | Factor |
|---|---|
| Sedentary - desk job, little exercise | 1.2 |
| Light - exercise 1–3 days a week | 1.375 |
| Moderate - exercise 3–5 days a week | 1.55 |
| Active - exercise 6–7 days a week | 1.725 |
| Very active - physical job or twice-daily training | 1.9 |
A worked example
A 30-year-old man, 175 cm and 70 kg, exercising lightly:
- BMR = (10 × 70) + (6.25 × 175) − (5 × 30) + 5 = 1,649 kcal
- TDEE = 1,649 × 1.375 = 2,267 kcal
To lose about 0.5 kg a week he would eat roughly 1,767 kcal; to gain at the same rate, roughly 2,767 kcal.
Where the estimate goes wrong
The activity multiplier is the weak link. The BMR equation is fitted to measured data. The multipliers are broad categories, and most people place themselves a category too high. If your weight is not moving as predicted after three weeks, your true multiplier is the thing to revise - not the equation.
Body composition is invisible to it. Muscle burns more at rest than fat does. Two people of identical height, weight, age and sex can differ by 200–300 kcal a day. Equations using lean body mass, such as Katch-McArdle, are more accurate if you know your body fat percentage.
Metabolism adapts. Sustained deficits reduce both BMR and spontaneous movement. This is why weight loss slows even when adherence does not, and why recalculating every 4–5 kg matters.
Using the number properly
Track your weight as a weekly average rather than a daily reading - day-to-day swings are mostly water and gut contents. If the weekly average is not moving in the direction you want after two to three weeks, adjust intake by 10% and reassess.
Very low intakes are counterproductive and can be dangerous. Sustained intake below roughly 1,500 kcal for men or 1,200 kcal for women makes adequate protein and micronutrients hard to reach and should only happen under clinical supervision.
Common questions
What is the difference between BMR and TDEE?
BMR is what your body burns at complete rest just staying alive - breathing, circulating blood, maintaining temperature. It is typically 60–70% of your total. TDEE adds movement, exercise and the energy cost of digesting food. TDEE is the number to eat against; BMR is a floor you should not deliberately eat below.
Why does the calculator ask for sex at birth?
The Mifflin-St Jeor equation was derived with a constant that differs by sex, reflecting average differences in lean body mass. It is a limitation of the underlying research rather than a design choice, and it means the equation is least accurate for anyone whose body composition differs markedly from the population it was fitted to.
How accurate is this?
The Mifflin-St Jeor equation predicts measured resting energy expenditure within 10% for about 80% of people. The activity multiplier is much rougher - self-reported activity is notoriously overestimated. Treat the result as a starting point, then adjust based on what actually happens to your weight over two to three weeks.
Is a 500 calorie deficit always right?
It is a convention, not a rule. A 500 kcal daily deficit predicts roughly 0.45 kg (1 lb) of loss a week, based on the approximation that a pound of fat stores about 3,500 kcal. In practice, metabolic adaptation slows this over time, and very large deficits cost lean mass. A deficit of 10–20% below TDEE is more sustainable than a fixed number.
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