I Built a Body Health Calculator Suite — BMI Made Me Do It

BMI is a terrible metric and I am tired of pretending it is not. It was invented in the 1830s by a Belgian mathematician studying population averages, not individual health. It does not distinguish between muscle and fat. It does not account for body composition, frame size, or where you carry your weight.

So I built BodyCalc Tool — calculators that actually tell you something useful.

Body Fat Calculator

Uses the US Navy method (neck + waist + height for men, + hips for women). This method has been validated in multiple studies and correlates closely with DEXA scan results. More importantly, it is measurable at home with a $2 tape measure.

I originally tried to integrate bioelectrical impedance formulas from smart scales, but the accuracy varies so wildly between devices that it was not worth it. The Navy method is old but at least it is consistent.

TDEE Calculator

Total Daily Energy Expenditure using the Mifflin-St Jeor equation, with activity multipliers from sedentary to athlete.

The activity multiplier is where most calculators get sloppy. "Moderate exercise 3-5 days/week" means different things to different people. I added concrete examples: "Moderate = you break a sweat and breathe harder but can talk. Example: 30 min jog at 6mph."

Waist-to-Hip Ratio

A better cardiovascular risk predictor than BMI. Ratio > 0.90 (men) or > 0.85 (women) correlates with higher heart disease risk even if BMI is "normal." Most people have never measured this.

Ideal Weight + Protein Calculators

Ideal weight uses four formulas (Robinson, Miller, Devine, Hamwi) and shows the range — no single formula is "right." Protein calculator uses the research-backed 0.8g/kg to 2.2g/kg range based on activity level.

What I learned

1. People want context, not numbers. A raw body fat percentage means nothing without knowing what is healthy for your age and gender.
2. Imperial + metric is non-negotiable. Half my users are American (lbs/inches), half international (kg/cm).
3. Privacy matters. All calculations happen in the browser. Nothing stored server-side.

→ bodycalctool.com — all calculators free, no signup