About Us
Free Health Tools,
Built with Science
FitFuel Tools was built with one mission: give everyone access to accurate, science-backed health and nutrition calculators — completely free, forever, with no sign-up required.
Our Mission
Too many health tools online either require expensive app subscriptions, bury results behind paywalls, or use oversimplified formulas that produce inaccurate results. We set out to fix that.
Every calculator on FitFuel Tools uses the same evidence-based formulas trusted by registered dietitians, personal trainers, and sports scientists. We publish the formula behind every result so you can understand how your number was calculated — not just what it is.
What We Offer
BMI Calculator
WHO-standard body mass index calculation
Calorie Calculator
Mifflin-St Jeor BMR + TDEE targets
Macro Calculator
Goal-based protein, carb & fat splits
Water Intake
Daily hydration targets by body weight
Body Fat %
US Navy circumference method
Protein Intake
ISSN evidence-based protein guidelines
Sleep Calculator
90-minute sleep cycle optimisation
Ideal Weight
4 clinical formulas + BMI range
One Rep Max
5 formulas: Epley, Brzycki & more
Running Pace
Pace + race time projections
Heart Rate Zones
Karvonen method, 5 training zones
Waist-to-Hip Ratio
WHO cardiovascular risk classification
Lean Body Mass
Boer, James & Hume formulas
Calorie Deficit
Safe deficit + weekly loss projections
Steps to Calories
MET-based walking calorie burn
Body Surface Area
Mosteller, DuBois & Haycock formulas
Pregnancy Due Date
Naegele's Rule + milestone timeline
TDEE Calculator
Full energy expenditure breakdown
Age Calculator
Exact age, days lived & countdown
Our Principles
Science-first
Every formula we use is sourced from peer-reviewed research and established clinical guidelines. We cite our sources on each calculator page.
Privacy by design
All calculations run entirely in your browser. The health data you enter is never sent to our servers, never stored, and never seen by us.
Always free
Our tools are free to use with no sign-up, no paywall, and no premium tier. We keep the lights on with non-intrusive advertising.
Honest about limitations
We clearly explain what our calculators can and can't do. We always recommend consulting qualified healthcare professionals for medical decisions.
Formula Transparency
We believe you should understand how your results are calculated. On every calculator page, we explain the formula being used and its origin. For example:
- Our calorie calculator uses the Mifflin-St Jeor equation (1990), validated as the most accurate BMR formula for most adults
- Our body fat calculator uses the US Navy circumference method (Hodgdon & Beckett, 1984)
- Our ideal weight calculator presents results from four clinical formulas (Hamwi, Devine, Robinson, Miller) alongside the WHO BMI range
Important Notice
FitFuel Tools is an informational resource, not a medical service. Our calculators produce estimates based on population-level formulas. Results should never replace advice from a qualified doctor, dietitian, or health professional. See our full Medical Disclaimer.
Get in Touch
We love hearing from users — whether it's a suggestion for a new calculator, a formula correction, or general feedback. Reach us at hello@fitfueltools.com