TDEETotal Daily Energy Expenditure
The total calories you burn in a day, from all activity and metabolism.
TDEE (Total Daily Energy Expenditure) is the total number of calories your body uses in a day. It is the sum of four things: your basal metabolic rate, the energy cost of digesting food, deliberate exercise, and all the other movement you do without calling it exercise, which is NEAT.
The proportions surprise people. For most sedentary adults, basal metabolic rate is somewhere around two thirds of the total, digestion takes roughly a tenth, and the gym session that feels like the main event is often the smallest slice of the day. Walking, standing and fidgeting frequently outweigh it.
It matters because it is the anchor for any nutrition goal. Eating below your TDEE drives fat loss, above it supports weight and muscle gain, and around it maintains. Every macro split, meal plan and diet name operates inside that arithmetic rather than around it.
Every estimate of it is a prediction, not a measurement. The usual method computes basal rate from an equation such as Mifflin St Jeor and multiplies by an activity factor. The equation itself is decent: the original paper found fat free mass to be the single best predictor of resting expenditure, and noted that the older Harris Benedict equations overestimated it by about 5%. The activity multipliers are the weak link, because self-reported activity is where honest people go wrong.
So treat the number as a starting hypothesis and let the scales grade it. Hold intake steady for two or three weeks, track weight as a weekly average rather than daily, and adjust the estimate to the trend you actually see. That correction is worth more than any refinement of the formula.
Total expenditure is also more stable across adult life than the folklore suggests. A large study using doubly labelled water across ages 8 days to 95 years found that, once fat free mass is accounted for, energy expenditure holds steady from about 20 to 60 years of age and only then declines. The metabolism that supposedly collapses at 30 does not show up in the data; the change in how much people move does.
In practice: estimate it with our TDEE calculator, set the deficit or surplus with the calorie deficit calculator, and re-estimate whenever your bodyweight moves by a few kilograms, because the number moves with you.