What TDEE means and why it matters

TDEE = Total Daily Energy Expenditure. It's the total number of calories your body burns in a 24-hour period — at rest, in motion, digesting food, and maintaining temperature. It's the central number in any nutrition plan: eat less than TDEE and you lose weight; eat more and you gain. Get TDEE wrong and every other calculation is off.

TDEE has four components:

1. BMR (Basal Metabolic Rate) — calories burned at complete rest, just to keep your organs running. ~60–75% of TDEE for most people.
2. TEF (Thermic Effect of Food) — calories burned digesting and processing what you eat. Protein has the highest TEF (~25% of its calories go to digestion); fat the lowest (~3%). Roughly 10% of TDEE.
3. NEAT (Non-Exercise Activity Thermogenesis) — fidgeting, walking, standing, daily movement that isn't a planned workout. Highly variable between individuals (200–600+ cal/day difference).
4. EAT (Exercise Activity Thermogenesis) — your actual workouts. Smaller share of TDEE than people think — even an hour of running is only ~600 cal.

The Mifflin-St Jeor equation

The calculator uses the Mifflin-St Jeor equation (1990) for BMR, which independent research (the Frankenfield meta-analysis) found to be the most accurate predictive formula for non-obese adults:

Men:    BMR = 10 × weight_kg + 6.25 × height_cm − 5 × age + 5
Women:  BMR = 10 × weight_kg + 6.25 × height_cm − 5 × age − 161

Then multiply by an activity factor to get TDEE:

• Sedentary (desk job, little exercise): BMR × 1.2
• Lightly active (light exercise 1–3 days/week): BMR × 1.375
• Moderately active (3–5 days/week): BMR × 1.55
• Very active (6–7 days/week): BMR × 1.725
• Extremely active (twice-daily training, physical job): BMR × 1.9

How accurate is it?

For non-obese adults aged 19–82, Mifflin-St Jeor predicts BMR within 10% of measured values about 70% of the time. The biggest source of error in TDEE is the activity factor — most people overestimate. "Moderately active" really means structured exercise 3–5 days per week; if you just walk the dog twice, you're closer to lightly active.

For athletes, obese individuals, very lean individuals, and the elderly, Mifflin-St Jeor accuracy degrades. The Katch-McArdle formula (which uses lean body mass instead of total weight) is generally better for athletes — switch to it in the tool when known body fat % is available.

Using TDEE for goals

The calculator outputs three calorie targets based on your TDEE:

• Cut (lose fat): TDEE − 500. A 500 cal/day deficit produces roughly 0.5 kg (~1 lb) of fat loss per week. Going more aggressive than 25% below TDEE risks muscle loss, energy crashes, and rebound.
• Maintain: TDEE. Recomposition (gaining muscle while losing fat) is possible at maintenance for beginners and returning lifters; less effective for advanced athletes.
• Bulk (gain muscle): TDEE + 300. A small surplus minimises fat gain. "Dirty bulks" at +1000 produce far more fat than muscle.

Pair with the Macro Calculator for the protein/carb/fat breakdown of your target calories.