Daily energy expenditure and total energy needs
Total daily energy expenditure, or TDEE, estimates how much energy the body uses in one day. It starts with basal metabolic rate, then adds the effect of daily activity, planned exercise, non-exercise activity thermogenesis, and the thermic effect of food. This helps show why total energy needs are higher than resting energy needs alone.
Core formulas
The calculator first adjusts BMR by the selected activity factor:
\[
\begin{aligned}
E_{\text{activity-adjusted}} &= BMR \cdot AF
\end{aligned}
\]
Exercise calories and non-exercise activity thermogenesis can then be added:
\[
\begin{aligned}
E_{\text{subtotal}} &= E_{\text{activity-adjusted}} + E_{\text{exercise}} + E_{\text{NEAT}}
\end{aligned}
\]
The thermic effect of food is estimated as a percentage of the subtotal:
\[
\begin{aligned}
E_{\text{TEF}} &= E_{\text{subtotal}} \cdot \frac{TEF\%}{100}
\end{aligned}
\]
Total daily energy expenditure is then:
\[
\begin{aligned}
TDEE &= E_{\text{subtotal}} + E_{\text{TEF}}
\end{aligned}
\]
Here, \(BMR\) is basal metabolic rate, \(AF\) is the activity factor, \(E_{\text{exercise}}\) is planned exercise energy, \(E_{\text{NEAT}}\) is non-exercise activity thermogenesis, and \(E_{\text{TEF}}\) is the thermic effect of food.
How to interpret results
The TDEE value represents an estimated maintenance calorie level. If goal mode is set to maintenance, the target intake equals TDEE. If deficit mode is selected, the target intake is below TDEE. If surplus mode is selected, the target intake is above TDEE.
- Use BMR as the resting baseline, not the full daily requirement.
- Activity factor increases the estimate according to lifestyle and movement level.
- Exercise and NEAT should be added carefully to avoid double-counting activity.
- Thermic effect of food is an estimate, not a fixed biological constant.
Example: if BMR is 1700 kcal/day and the activity factor is 1.55, activity-adjusted expenditure is 2635 kcal/day. Adding exercise, NEAT, and TEF gives a more complete estimate of daily energy needs.
This calculator is useful for physiology learning, nutrition education, activity-level comparisons, and understanding how maintenance, deficit, and surplus targets are built. It should not be treated as a medical or diet prescription because real energy needs depend on body composition, hormones, training status, illness, sleep, adaptive metabolism, and measurement accuracy.
