TDEE / BMR Calculator

What TDEE Actually Measures

Your Total Daily Energy Expenditure is the total calories your body burns in a day across four components: BMR (calories burned at complete rest to sustain basic functions — about 60–70% of TDEE), the thermic effect of food (digestion costs roughly 10% of calories consumed), non-exercise activity thermogenesis or NEAT (fidgeting, walking, standing), and deliberate exercise. The calculator uses the Mifflin-St Jeor equation for BMR, which research consistently shows is the most accurate formula for the general population.

Choosing the Right Activity Multiplier

The activity multipliers are the largest source of error in TDEE estimates. Most people underestimate sedentary time and overestimate how much they exercise. "Lightly active" (1.375×) means 1–3 days of actual exercise per week, not a job that involves occasional walking. If you exercise 4–5 days per week but sit for most of the rest of the day, use "moderately active" (1.55×). Athletes training twice daily are the rare case for "very active" (1.725×). When in doubt, choose one level lower than feels right and adjust based on real results.

Metabolic Adaptation: Why TDEE Shifts

TDEE is not fixed. In a sustained calorie deficit, the body adapts to conserve energy: BMR drops, NEAT decreases (unconscious movement reduces), and the thermic effect of food falls. After 8–12 weeks of dieting, your actual maintenance calories may be 10–15% below your calculated TDEE. This is sometimes called "metabolic adaptation" or "adaptive thermogenesis." A structured diet break — returning to maintenance calories for 1–2 weeks — can partially reverse this adaptation and improve adherence over the long term.

How to Use TDEE for Your Goal

For fat loss, a deficit of 300–500 calories per day produces 0.5–1 lb of loss per week — sustainable without significant muscle loss. Larger deficits (500–750 calories) accelerate loss but increase hunger, muscle breakdown risk, and adaptation. For muscle gain, a surplus of 200–300 calories above TDEE minimises fat gain while supporting growth. Recalculate every 4–6 weeks as your weight changes, since TDEE decreases as you lose mass and increases as you gain it.