Energy · 3 min read
TDEE Explained: Why the Number Is a Starting Point
Try it: TDEE and Calorie Target — Your maintenance calories, plus a target that matches the rate of loss you can hold.
Every calorie calculator gives you a confident number. None of them measured anything. Here is what the number is built from and how much of it you should trust.
The four parts
Total daily energy expenditure is the sum of four things:
- Basal metabolic rate. What you burn keeping the lights on — organs, brain, temperature. For most people this is the largest single share, typically somewhere in the region of 60 to 75 per cent of the total.
- The thermic effect of food. The energy cost of digesting what you eat, commonly cited around 8 to 10 per cent. Protein costs the most to process, which is a small side benefit of a higher-protein diet rather than a strategy on its own.
- Deliberate exercise. Usually far less than people assume. An hour of training is real but it is not the biggest lever.
- Everything else you do. Walking, standing, fidgeting, carrying things. This varies enormously between people and, importantly, it varies within the same person from week to week.
Where the estimate goes wrong
The basal part is calculated from height, weight, age and sex, and it is reasonably reliable. The problem is the activity multiplier. Two people select "trains three times a week" — one of them also walks 12,000 steps a day and the other drives everywhere. The gap between them is several hundred calories, and the calculator cannot see it.
That is the honest limitation. A TDEE calculator narrows the range from "no idea" to "probably within a few hundred calories". It does not produce a measurement.
How to find your real number
Two weeks, and the method is simple.
- Eat at the estimated maintenance figure, consistently, without trying to lose anything.
- Weigh yourself every morning under the same conditions.
- Average each week. Compare week two's average to week one's.
Steady means the estimate was close. Down half a kilogram a week means your true maintenance is roughly 500 calories higher than you were eating. Up means the reverse. That is your real number, and it beats any equation because it comes from you.
Why weekly averages, not daily weights
Daily bodyweight moves by a kilogram or more for reasons that have nothing to do with fat: salt, water, carbohydrate stored as glycogen, what is currently in your digestive tract, and how hard you trained. Reading single mornings is how people conclude that a working plan is failing on day four.
The number changes as you do
Lose weight and your maintenance falls — a smaller body costs less to run and moving it costs less. This is not your metabolism breaking; it is arithmetic. Recalculate every four to six kilograms rather than assuming the number from January still applies in May.
What to actually do with it
Set a deficit that matches a rate of loss you can hold rather than one that looks impressive — the TDEE and calorie target calculator lets you pick the rate and returns the target. Then set protein, because the size of the deficit determines how fast the weight comes off and protein determines how much of it is fat.
One thing worth saying plainly
If your estimate says 2,400 and you have been eating "about 1,800" for months without the scale moving, the likeliest explanation is not a broken metabolism. It is that "about 1,800" is not 1,800. Tracking honestly for a single week, weighing food rather than estimating, resolves this for most people — and it is not something you need to keep doing forever.
Questions I get asked
Which is more accurate, Mifflin-St Jeor or Harris-Benedict?
Mifflin-St Jeor is the more common modern default and performs at least as well. Neither is precise enough to be treated as a measurement.
Should I eat back the calories from my watch?
Wearable estimates of exercise burn are frequently high. If you eat them all back, a deficit can quietly disappear. Treat them as directional.
Read next
- Why Your Metabolism "Slows Down" on a Diet Metabolic adaptation is real, mostly explainable, and smaller than the internet claims. Here is what actually changes and which part you can control.
- How Fast Should You Lose Fat? Picking a rate of loss is the decision that determines how much muscle you keep and whether you finish the phase at all.
- How Much Protein You Actually Need The protein range that covers almost everyone, why a calorie deficit raises it, and the one-week test that shows whether you are actually hitting it.