Last updated: 3 August 2026
Reviewed by Jordan Makin, FA Level 2 Football Coach
Total Daily Energy Expenditure
Why this calculator offers a lean-mass option
The standard Mifflin-St Jeor formula (used by default above) is accurate for most people, but it has one well-known blind spot: it can't tell the difference between muscle and fat, because it only uses total weight. Someone who's leaner or more muscular than average burns more calories at rest than the standard formula assumes, because muscle tissue is more metabolically active than fat.
If you know your approximate body fat percentage, entering it switches the calculation to the Katch-McArdle formula, which uses your estimated lean body mass instead of total weight. This is the same adjustment several evidence-based fitness calculators (including Built With Science's TDEE tool) make specifically for leaner or more muscular users — it's not a different opinion about your metabolism, it's a formula built around a number the standard equation doesn't have access to.
If you don't know your body fat percentage, leave it blank — Mifflin-St Jeor remains a solid, well-validated default for the general population.
The components hidden inside TDEE
TDEE isn't one single thing — it's the sum of four distinct energy costs, and understanding each one explains why two people with identical "activity levels" on paper can have meaningfully different real-world TDEE:
| Component | What it is | Typical share of TDEE |
|---|---|---|
| BMR (Basal Metabolic Rate) | Energy to keep organs running at complete rest | ~60-70% |
| NEAT (Non-Exercise Activity Thermogenesis) | Fidgeting, walking, posture, all movement that isn't structured exercise | ~15-30%, highly variable person to person |
| TEF (Thermic Effect of Food) | Energy used to digest and process food itself | ~10% |
| EAT (Exercise Activity Thermogenesis) | Structured, deliberate exercise | ~5-15%, depends heavily on training volume |
NEAT is the biggest source of individual variation and the easiest one to underestimate — two people who both "sit at a desk all day" can genuinely differ by 300-400 calories/day in NEAT alone, purely from things like fidgeting, taking stairs, or standing versus sitting through calls.
Why TDEE changes over time — and isn't a trick
A common frustration is TDEE seeming to "drop" during a sustained diet, requiring further calorie cuts to keep losing weight. This is a real, well-documented phenomenon called adaptive thermogenesis:
- Lower body weight burns fewer calories at rest — a smaller body simply needs less energy to maintain itself, so BMR genuinely falls as you lose weight, independent of any metabolic "damage."
- NEAT often drops unconsciously during a diet — people in a calorie deficit tend to fidget less and move less without realising it, sometimes called "NEAT compensation."
- A modest additional adaptive effect exists — beyond what body-weight loss alone explains, sustained dieting can trigger a further, usually modest, drop in metabolic rate as a survival adaptation.
This is why recalculating TDEE periodically during a long diet — rather than trusting one number for months — keeps your targets accurate as your body genuinely changes.
Top picks compared
| Pick | Product | Best for | |
|---|---|---|---|
| Top pick | Digital Kitchen Scale | Accurate food weighing to precisely track calorie intake against your TDEE. | Check price → |
| Option | Calorie Tracking App | Log meals and track calorie intake vs your TDEE target automatically. | Check price → |
| Option | Nutrition for Athletes (Book) | How to use TDEE, macros and timing for sport performance and body composition. | Check price → |
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Frequently asked questions
What's the difference between BMR and TDEE?
BMR is calories burned at complete rest — just to keep organs functioning. TDEE adds the energy used for all daily movement and exercise. Most people's TDEE is 1.4-1.8× their BMR. TDEE is the number that actually matters for nutrition planning.
How accurate is TDEE?
Within 10-15% for most people. The main uncertainty is the activity multiplier — people consistently underestimate their sedentary time and overestimate their exercise intensity. Track calories for a week at your TDEE estimate and adjust if weight changes unexpectedly.