Total Daily Energy Expenditure (TDEE)
Total Daily Energy Expenditure (TDEE) is an estimate of how much energy the body uses in a full day.
It includes a resting baseline plus additional energy for daily activity. In most introductory nutrition and
health-metrics models, TDEE is approximated by multiplying a Basal Metabolic Rate (BMR) estimate by an
activity factor. This calculator uses that standard approach to produce practical, easy-to-interpret outputs.
Core relationship
The main model used is:
\[
\mathrm{TDEE} = \mathrm{BMR}\times f
\]
where \(f\) is the activity factor selected from presets (or entered as a custom value).
BMR is either computed from body data (as in the BMR calculator) or entered manually.
Activity level multipliers
Activity factors are convenient multipliers that roughly account for energy used beyond resting needs.
Common presets (labels may vary slightly across sources) include:
\[
\begin{aligned}
\text{Sedentary} &:\ f \approx 1.20 \\
\text{Light} &:\ f \approx 1.375 \\
\text{Moderate} &:\ f \approx 1.55 \\
\text{Very active} &:\ f \approx 1.725 \\
\text{Athlete / extra active} &:\ f \approx 1.90
\end{aligned}
\]
These factors are intended for quick planning and are not a substitute for measured energy expenditure.
Real needs vary with job demands, training type, body composition, sleep, and other biological factors.
Using BMR: automatic vs manual
The calculator supports two ways to supply BMR:
-
Auto BMR: compute BMR from sex, age, height, and weight using a selected equation
(Mifflin–St Jeor or revised Harris–Benedict).
-
Manual BMR: type in a known BMR value directly (in kcal/day).
The TDEE calculation uses the same units (kcal/day) internally, then reports both kcal/day and kJ/day.
Energy unit conversion: kcal/day ↔ kJ/day
The conversion used is:
\[
1\ \text{kcal} = 4.184\ \text{kJ}
\]
Therefore:
\[
\mathrm{TDEE}_{\text{kJ/day}} = \mathrm{TDEE}_{\text{kcal/day}}\cdot 4.184
\]
Optional goal calories: cut or bulk
Many planning scenarios begin with TDEE and then apply a daily deficit (cut) or surplus (bulk).
This calculator supports two adjustment styles:
- Fixed adjustment: add or subtract a chosen number of kcal/day.
- Percent adjustment: add or subtract a chosen percent of TDEE.
Fixed kcal/day adjustment
\[
\text{Target} =
\begin{cases}
\mathrm{TDEE} - \Delta, & \text{cut (deficit)} \\
\mathrm{TDEE} + \Delta, & \text{bulk (surplus)}
\end{cases}
\]
where \(\Delta\) is a fixed number of kcal/day.
Percent of TDEE adjustment
If the adjustment is entered as a percent \(p\%\), it is first converted to kcal/day:
\[
\Delta = \mathrm{TDEE}\cdot \frac{p}{100}
\]
Then the same target equation is applied:
\[
\text{Target} =
\begin{cases}
\mathrm{TDEE} - \Delta, & \text{cut (deficit)} \\
\mathrm{TDEE} + \Delta, & \text{bulk (surplus)}
\end{cases}
\]
Optional weekly change estimate (very basic)
A simple weekly energy difference can be computed as daily adjustment multiplied by 7:
\[
\Delta_{\text{week}} = \Delta_{\text{day}}\cdot 7
\]
This weekly number is included only as basic arithmetic. It does not model metabolic adaptation,
changing training volume, or changes in body mass over time.
Interpreting the graphs
-
Stacked bar: shows how the BMR baseline plus the activity add-on combine to form TDEE.
-
Activity comparison strip: shows the predicted TDEE across standard activity levels,
highlighting the selected level.
-
Goal slider/meter (if enabled): shows how a deficit or surplus shifts the calorie target relative to TDEE.
Important note
TDEE is an estimate. For many people it is accurate enough for planning, but it can be off by several percent.
If using TDEE to guide nutrition changes, adjust gradually and monitor trends over time
(energy, performance, hunger, and body measurements) and consult a qualified professional when needed.
