What it is made of
- Resting energy (BMR). The largest share, used just to keep you alive.
- Digesting food. The body spends some energy processing what you eat, often cited as around 10 percent of intake.
- Everyday movement. Walking, standing, chores, fidgeting. This varies a lot between people and can be larger than planned exercise.
- Exercise. Deliberate training, usually the smallest of the four for most people.
How calculators estimate it
A calculator starts with BMR and multiplies it by an activity factor: 1.2 for a sedentary day, 1.375 for light exercise, 1.55 for moderate, 1.725 for hard daily exercise and 1.9 for very hard training or a physical job. For a BMR of 1,320 kcal, that gives about 1,584 kcal at sedentary and 2,046 kcal at moderate. The factors are common rules of thumb, not measurements, so the result is an estimate.
Using it
Treat TDEE as a starting point for maintenance, then adjust from real results: weigh yourself under similar conditions over two to three weeks and move your intake by a small amount if your weight drifts. Use the BMR and TDEE Calculator for the first estimate.
Common misunderstanding
Most people choose a more active level than they really live. If you hesitate between two, take the lower one. Medical conditions, pregnancy and growth change energy needs, so see a doctor or dietitian rather than relying on a calculator in those cases.
Source: activity factors are the widely used Harris-Benedict-style multipliers applied to a BMR from Mifflin et al., Am J Clin Nutr 1990;51(2):241–247 (doi). General information only, not medical advice.