Healthy Calculator Hub

Healthy Calculator Hub is a free set of 33 health and fitness calculators, built so you can see exactly where each number comes from.

Most calculator sites hand you a figure and expect you to trust it. Every page here shows the formula it used and links the primary source behind it - over 200 citations to CDC, WHO, NIH, NHS, ACOG and the original research papers.

What's inside:

→ Body composition - BMI, body fat, FFMI, lean body mass, waist-to-hip, waist-to-height, ideal weight, body surface area, Army body fat, reverse BMI

→ Calories and energy - TDEE, BMR, calories burned, calorie deficit, weight-loss timeline, weight-loss percentage

→ Nutrition - macros, protein, carbs, water intake, intermittent fasting

→ Fitness - one-rep max, running pace, swim pace, run-walk, VO2 max, race-time predictor, target heart-rate zones, steps to calories, steps to miles

→ Everyday health - sleep cycles, sleep debt, pregnancy due date

Details that make a difference:

→ Heart-rate zones use the Tanaka (2001) revised formula, not the outdated 220-age

→ TDEE uses Mifflin-St Jeor with FAO/WHO/UNU activity multipliers

→ Results recalculate live as you type, and switching units (kg/lb, cm/ft) converts in place

→ 23 plain-language guides sit alongside the calculators

Free, no sign-up, no paywall. It's an independent project built by one person, not a medical service - the citations are there so you can check the working yourself.