TDEE Explained: How Many Calories You Actually Burn in a Day

BMR: the engine at idle

Your basal metabolic rate is what you'd burn lying motionless for 24 hours — the cost of running a brain, heart, lungs, and 37 trillion cells. It's typically 60–70% of everything you burn, and it's driven mostly by body size: the Mifflin-St Jeor equation estimates it from weight, height, age, and sex.

For a 30-year-old man at 175 cm and 75 kg, BMR comes out around 1,700 kcal. The equation carries roughly ±10% accuracy for most people — good enough to start, not gospel.

From BMR to TDEE

TDEE multiplies BMR by an activity factor between 1.2 (sedentary) and 1.9 (physical job plus hard training). Our example person with light exercise lands around 2,300 kcal a day.

Here's where most plans break: people overestimate their activity level. Three gym sessions a week on top of a desk job is 'light to moderate', not 'active' — the workouts burn less than people think, and sitting the other 165 hours a week counts too. When in doubt, pick the lower factor.

Setting a deficit that sticks

A pound of body fat stores about 3,500 kcal, so eating 500 below TDEE loses roughly a pound a week. Bigger deficits work faster but cost more muscle and willpower; most people sustain a 300–500 kcal deficit far longer than an aggressive cut.

For gaining muscle, the surplus should be modest — around 200–300 kcal above TDEE with progressive strength training. Bigger surpluses mostly add fat.

Calibrate against reality

The calculator gives a starting point; your scale gives the truth. Eat your calculated target for two to three weeks and watch the weekly average weight. Flat when you expected loss? Cut 150–200 kcal. Falling too fast? Add some back. Two or three adjustment cycles beats any formula's precision — you're measuring your actual metabolism.