Mifflin-St Jeor vs Katch-McArdle
Mifflin-St Jeor estimates your basal metabolic rate (BMR) from age, sex, height, and weight, and is considered one of the more accurate general-population formulas. Katch- McArdle instead uses lean body mass, which is more precise if you know your body-fat percentage — useful for people who are more muscular or leaner than average, where weight alone under- or over-estimates true metabolic needs.
From BMR to TDEE
BMR is the energy your body burns at rest. TDEE multiplies BMR by an activity factor (sedentary, lightly active, moderately active, very active) to estimate total daily burn including movement and exercise. TDEE — not BMR — is the number to use when setting a calorie target, since it reflects your actual day, not just resting metabolism.
Setting a target: cut, maintain, or bulk
A sustainable deficit for fat loss is typically 15–25% below TDEE; a more aggressive cut risks muscle loss and fatigue. Recomposition or lean bulking targets are usually within a few hundred calories of TDEE in either direction. The calculator applies these common ranges to your specific TDEE so the targets are calibrated to you, not a generic number.
Why use UtilityApps for this
All calculations run locally in your browser — your body stats are never uploaded or stored. No signup, no meal-plan upsell, just the numbers.