About FitCalculator

FitCalculator is a collection of free, science-based health and fitness calculators built for anyone who wants to make better decisions about their body and training. Every tool on this site is grounded in peer-reviewed research and established formulas used by nutritionists, coaches, and medical professionals around the world.

Why we built this

Most fitness calculator sites are cluttered with pop-ups, paywalls, and outdated interfaces. We wanted something different — tools that are fast, clean, mobile-friendly, and actually pleasant to use. No account required, no email harvesting, no hidden upsells. Just open the page, enter your numbers, and get results.

Our approach to accuracy

We never rely on a single formula. Where possible, every calculator shows results from multiple established equations so you can see the range rather than a single number. For example, our TDEE calculator uses the Mifflin-St Jeor, Harris-Benedict, and Katch-McArdle equations side by side. Our one rep max calculator averages five proven formulas. This multi-formula approach gives you a more realistic picture than any single estimate.

All formulas are sourced from published research and widely accepted standards. We cite the Mifflin-St Jeor equation (1990) for basal metabolic rate, the U.S. Navy body composition method for body fat estimation, WHO guidelines for BMI classification, and the European Food Safety Authority recommendations for water intake. Every calculator page includes a detailed explanation of the methods used.

What we offer

Our current suite of calculators covers the fundamentals of fitness and nutrition planning. The TDEE calculator helps you find your daily calorie needs and macro targets. The BMI calculator gives you a quick weight classification with both the standard and height-corrected New BMI formula. The body fat calculator estimates your body composition using tape measurements. The one rep max calculator lets lifters estimate their max strength and plan percentage-based training. And the water intake calculator provides personalized hydration targets based on your weight, activity, and climate.

We are continually expanding the site with new tools. Upcoming calculators include a pregnancy due date calculator, a heart rate zone calculator for cardio training, an ideal weight calculator comparing multiple medical formulas, and a protein intake calculator tailored to specific fitness goals.

Important disclaimer

FitCalculator provides estimates based on population-level formulas. Individual results will vary based on genetics, medical conditions, body composition, and other factors that no calculator can fully account for. Our tools are designed for educational and informational purposes only. They are not a substitute for professional medical advice, diagnosis, or treatment.

If you have specific health concerns, are managing a medical condition, or are planning significant changes to your diet or exercise routine, please consult a qualified healthcare professional, registered dietitian, or certified personal trainer.

Privacy and data

We take your privacy seriously. FitCalculator does not collect, store, or transmit any personal data you enter into the calculators. All calculations happen locally in your browser. We do not require accounts, and we do not use cookies for tracking. The only third-party service on the site is Google AdSense, which may use cookies for ad personalization — you can read more about this in our privacy policy.

Contact

Have a suggestion, found a bug, or want to request a new calculator? We would love to hear from you. Visit our contact page to get in touch. We read every message and aim to respond within 48 hours.

Technical details

FitCalculator is built with Next.js and React, hosted on Vercel, and styled with Tailwind CSS. The site is statically generated for maximum speed and SEO performance. Every page scores 90 or above on Google PageSpeed Insights. The entire codebase is lightweight, with no unnecessary dependencies — because a fast calculator site should load faster than you can blink.