TDEE Calculator

The four things you burn calories on

Your resting metabolic rate is the largest share, usually 60 to 70% of the total. It is what your body spends staying alive: pumping blood, maintaining temperature, repairing tissue. You burn most of your calories doing nothing.

The thermic effect of food accounts for roughly 10%. Digestion itself costs energy, and protein costs the most, which is one reason higher protein intake helps during a deficit.

Deliberate exercise is usually the smallest piece, often 5 to 10% for most people. This surprises those who assume the gym is where the calories go.

The remainder is non-exercise activity thermogenesis: fidgeting, standing, walking to the kitchen, gesturing while you talk. It varies enormously between individuals and it quietly falls when you diet, which is a major reason weight loss slows.

Which equation this uses

This calculator uses Mifflin-St Jeor, which most current clinical guidance prefers over the older Harris-Benedict equation. It estimates your resting rate from weight, height, age, and sex, then multiplies by an activity factor.

Every one of these equations is a population average. Two people matched on all four inputs can differ by 200 to 300 calories a day in real expenditure. The equation cannot see your thyroid function, your muscle mass, or how much you move without noticing.

Pick your activity level honestly

This is where most people get a wrong answer. The activity multiplier is the single largest source of error in the whole calculation, and almost everyone overestimates.

If you have a desk job and train three times a week, you are lightly to moderately active, not very active. Very active describes hard training six or seven days a week. Extremely active describes manual labour or twice-daily training, not an enthusiastic gym habit.

When in doubt, choose the lower option. It is easier to add calories after a few weeks of faster-than-expected loss than to work out why nothing is happening.

Treat the output as a hypothesis

The right way to use this number is as a starting point to test. Eat at the estimate for two to three weeks, weigh yourself consistently under the same conditions, and watch the trend rather than any single day.

If weight holds steady, the estimate was close. If it moves, adjust by 100 to 200 calories and observe again. Your own data beats any formula within a month.