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Part of the CalcProMaster guides library · Updated September 2026
Health metrics are only useful when you know what they measure, what they ignore, and when they don't apply. These guides cover both the formula and its limits.
The two formulas here are simple; the honest part is what they assume. BMI = weight ÷ height² — a population-screening ratio that cannot distinguish muscle from fat. TDEE = BMR × activity multiplier — and the multiplier (1.2 sedentary to 1.9 very active) is the least precise number in the whole chain: two people with identical stats can differ by several hundred calories in reality. The calories guide shows how to pick a multiplier honestly and adjust from observed results instead of trusting the first estimate.
Every figure in this section is a reference, not a prescription. Formulas like Mifflin-St Jeor are population regressions — they're right on average and uncertain for any individual. That's why each guide ends by naming what the metric cannot see, and why the blog's BMI explainer pairs the formula with companion measurements rather than treating one number as a verdict.
For anyone changing weight or fitness, the working method is: compute a starting estimate, hold it for two to three weeks while recording actual outcomes, then adjust by observed reality — roughly 100–200 kcal at a time. That loop (estimate → observe → adjust) is more reliable than any formula refinement, because it uses your body's actual response instead of a population average. The calculators give you the honest starting point; the record-keeping makes it yours.
The weight/height formula, BMI categories, what BMI ignores (muscle mass, age, ethnicity), and the honest limits of the metric.
The Mifflin-St Jeor BMR formula, activity multipliers, realistic deficit targets, and how to read the scale honestly.
BMI Calculator BMR Calculator Calorie Calculator Ideal Weight Calculator