What is TDEE?
TDEE stands for total daily energy expenditure: every calorie your body burns in 24 hours. It has three parts. Your basal metabolic rate (BMR) covers the machinery of staying alive and makes up roughly 60–70% of the total. Physical activity — training, walking, and all the small movement researchers call NEAT — adds another 20–30%. Digesting food costs about 10%, the thermic effect of food.
Eat close to your TDEE and your weight holds steady. Eat under it and you lose; over it and you gain. That is why this one number is the anchor for every calorie target.
How this TDEE calculator works
The Mifflin-St Jeor equation
By default we estimate BMR with the Mifflin-St Jeor equation, published in the American Journal of Clinical Nutrition in 1990 and still the equation the American Academy of Nutrition and Dietetics recommends for the general population:
- Men: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5
- Women: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age − 161
The Katch-McArdle formula
If you enter a body fat percentage, we switch to Katch-McArdle: BMR = 370 + 21.6 × lean mass (kg). Because it works from lean mass instead of total weight, it handles very muscular and very lean bodies better. It is only as good as the body fat number you feed it.
Why not Harris-Benedict?
The older Harris-Benedict equation (1918) tends to overestimate modern, more sedentary populations by roughly 5%. Mifflin-St Jeor replaced it in clinical practice for exactly that reason, so we use it as the default and skip the legacy option.
Your BMR is then multiplied by an activity factor to get TDEE. The multipliers come from the FAO/WHO physical activity level framework.
Activity multipliers, explained honestly
| Level | Multiplier | What it looks like in a real week |
|---|---|---|
| Sedentary | 1.2 | Desk job, under ~5,000 steps, no regular training |
| Lightly active | 1.375 | 1–3 workouts a week, or an on-your-feet job |
| Moderately active | 1.55 | 3–5 real workouts a week, consistent steps |
| Very active | 1.725 | Hard training 6–7 days a week |
| Extra active | 1.9 | Physical job plus daily training, or two-a-days |
This is where TDEE estimates go wrong. Training three times a week feels like a lot, but if the rest of your day is a chair, you are Light, not Moderate. Picking one level too high inflates the result by 200–300 calories a day — enough to erase an intended deficit entirely.
How to use your TDEE
To lose weight
Subtract 250–500 calories from your TDEE. That produces roughly 0.25–0.5 kg (0.5–1 lb) of loss per week without wrecking your energy or your training. Larger deficits work faster but are harder to hold and cost more muscle. Stay above 1,200 calories a day unless a doctor is supervising you.
To maintain
Eat your TDEE. This is also the number to hold for a few weeks after a long diet before you decide what comes next.
To gain muscle
Add 200–300 calories over TDEE and train hard. Bigger surpluses mostly add fat. Pair the surplus with enough protein — the protein calculator gives you a target by body weight.
When to recalculate
Every four to six weeks, or whenever your weight moves by about 4–5 kg (10 lb). Your TDEE follows your body: as you get lighter it drops, as you add muscle it rises.
How accurate is this?
For most people, formula estimates land within about 10% of what a metabolic lab would measure. The equation is rarely the weak point — the self-rated activity level is. The fix is simple: eat at the estimate for two to three weeks, weigh yourself daily, and compare the trend to the prediction. If the scale disagrees, shift your intake by 100–200 calories and re-test. Real data beats any formula, which is exactly what a tracking app is for.
