About this reference
Why one BMI number isn’t the point
Most BMI calculators divide weight by height squared and hand back a category. That takes two seconds and tells you almost nothing actionable. BMI Tracker calculates seven metrics from the same four inputs — height, weight, age, activity — because a single number is rarely the useful part.
What it measures
Adjust the sliders on the dashboard and all seven update together, live: BMI, healthy weight range, estimated body fat, ideal body weight, daily calorie targets, protein and hydration. Nothing is submitted or stored — the maths runs in your browser and the result is thrown away the moment you close the tab.
Each metric is built to be read alongside the others, not in isolation. A BMI in the healthy range paired with a high body-fat estimate tells a different story than either number alone. That pairing is the actual point of a dashboard over a single calculator.
What's exact and what's estimated
BMI is exact — it's arithmetic on the height and weight you enter, nothing more. Every other metric here is a population-level estimate, useful as a reference point but not a substitute for direct measurement or clinical advice.
Body fat percentage in particular carries a real margin of error against DEXA scanning or hydrostatic weighing, and will overestimate fatness in very muscular people. Calorie needs (TDEE) can reasonably vary ±15–20% from any individual's actual burn. Ideal body weight is a single clinical reference point, not a personal target — healthy weight varies by frame and muscle mass.
The formulas, by metric
| Metric | Formula | Source |
|---|---|---|
| BMI | weight (kg) ÷ height (m)² | WHO classification — ref. 1 |
| Healthy weight range | BMI 18.5–24.9 solved for your height | WHO — ref. 1 |
| Body fat % | (1.20 × BMI) + (0.23 × age) − (10.8 × sex) − 5.4 | Deurenberg et al., 1991 — ref. 2 |
| Ideal body weight | 50 kg (M) / 45.5 kg (F) + 2.3 kg per inch over 5 ft | Devine formula, 1974 — ref. 3 |
| Calorie needs (TDEE) | Mifflin–St Jeor BMR × activity factor | Mifflin & St Jeor, 1990 — ref. 4 |
| Protein target | 0.8–2.0 g per kg, scaled by activity | WHO / ISSN guidelines — ref. 5 |
| Hydration | 35 ml per kg, scaled by activity | EFSA Dietary Reference Values — ref. 6 |
What this tool is — and isn't
BMI Tracker is an educational reference. Every number is a population-level statistical estimate, useful as a starting point, not a diagnosis. A BMI in the overweight range doesn't mean you're unhealthy; a BMI in the normal range doesn't mean you are. BMI itself was devised by Adolphe Quetelet in the 1830s as a population-statistics tool, not an individual clinical measure — a distinction that gets lost in how it's commonly used today.
If a number on this dashboard concerns you, the right next step is a conversation with a doctor or registered dietitian, not a second calculation.
References
- World Health Organization. Obesity and overweight — fact sheet, 2024.
- Deurenberg P, Weststrate JA, Seidell JC. Body mass index as a measure of body fatness. Br J Nutr, 1991.
- Devine BJ. Gentamicin therapy. Drug Intell Clin Pharm, 1974 (origin of the Devine ideal-body-weight formula).
- Mifflin MD, St Jeor ST, et al. A new predictive equation for resting energy expenditure. Am J Clin Nutr, 1990.
- World Health Organization / International Society of Sports Nutrition. Protein intake guidelines for sedentary and active adults.
- European Food Safety Authority. Scientific Opinion on Dietary Reference Values for water, 2010.
Questions or corrections?
If a formula, source, or figure on this site looks wrong, tell us — we'd rather fix it than leave it.
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