TDEE Calculator

Your Total Daily Energy Expenditure (TDEE) is the total number of calories your body burns in 24 hours — the true maintenance figure that sits at the heart of every nutrition strategy. Get it right and you have a precise starting point for fat loss, muscle gain, or performance. Get it wrong and months of effort can stall for no apparent reason.

What Actually Makes Up Your TDEE
TDEE has four components. Your Basal Metabolic Rate (BMR) — what the calculator shows first — accounts for roughly 60–75% and represents the energy your body burns just to stay alive: heartbeat, breathing, temperature regulation, organ function. Exercise activity (EA) adds another 15–30% for most people. Diet-induced thermogenesis (DIT) contributes around 10% — your body burns calories just digesting food, particularly protein. The fourth and most underappreciated component is Non-Exercise Activity Thermogenesis (NEAT).

NEAT: The Hidden Variable
NEAT encompasses every movement that is not formal exercise — fidgeting, walking to your car, standing at your desk, gesturing while talking. Research by Dr. James Levine at the Mayo Clinic found that NEAT can vary by up to 2,000 calories per day between two people of similar size. Lean people tend to fidget and move spontaneously far more than sedentary individuals — and this explains much of why some people seem to "eat whatever they want" without gaining weight. NEAT is also the first thing that drops when you diet, partly explaining why weight loss slows after several weeks.

Adaptive Thermogenesis: Why Your Metabolism Fights Back
When you eat in a prolonged calorie deficit, your body responds by reducing TDEE by 5–15% beyond what simple weight loss would predict. This adaptive thermogenesis (sometimes called metabolic adaptation) occurs through reduced NEAT, lowered thyroid hormone output, and decreased thermogenesis. A 500 cal/day deficit that should theoretically produce 0.5 kg of fat loss per week often produces less over time — not because of "broken metabolism," but because the body is defending its weight. Diet breaks and refeeds partially reverse this adaptation.

Mifflin-St Jeor vs. Harris-Benedict
The Mifflin-St Jeor equation (1990) is the formula used here and is consistently the most accurate for most populations, validated against indirect calorimetry in multiple studies. The older Harris-Benedict equation (1919, revised 1984) tends to overestimate BMR by about 5% in modern, less physically active populations. For very obese individuals, the Katch-McArdle formula (which uses lean body mass rather than total weight) can be more accurate, but it requires body fat percentage measurement.

Why Fitness Trackers Overestimate Burn
Wrist-based wearables (Apple Watch, Fitbit, Garmin) consistently overestimate calorie burn during exercise by 15–40% in published validation studies. They also tend to overestimate NEAT. This creates a systematic error: people eat back "exercise calories" they did not fully burn, inadvertently eating at maintenance or even a surplus while believing they are in a deficit. If you use a tracker, consider eating back only 50–70% of reported exercise calories until you have 4–6 weeks of scale data to calibrate against.

Formula Limitations for Muscular Individuals
The Mifflin formula uses total body weight, which means very muscular individuals (bodybuilders, strength athletes) will have their BMR underestimated — muscle is metabolically expensive tissue that burns more calories at rest than fat. Conversely, the formula slightly overestimates BMR for individuals carrying significant excess body fat. If you are considerably above or below average body fat levels, treat these numbers as a starting estimate and adjust based on 2–3 weeks of actual intake versus weight change data.