HydraFit.online brings together accurate, science-based calculators for weight, nutrition, fitness, sleep, vitals and women's health — all free, private, and instant.
Every calculator is built on trusted clinical formulas and designed for clarity, speed, and accuracy.
Calculate your Body Mass Index instantly with metric or imperial units and see your healthy weight range.
Use this tool →Calculate your Basal Metabolic Rate (BMR) — the calories you burn at rest — using the Mifflin-St Jeor equation.
Use this tool →Calculate your Total Daily Energy Expenditure and get a personalized calorie target for weight loss, maintenance or muscle gain.
Use this tool →Estimate your ideal body weight using four trusted medical formulas: Devine, Robinson, Miller and Hamwi.
Use this tool →Estimate your body fat percentage using the US Navy circumference method — no calipers needed.
Use this tool →Calculate your waist-to-hip ratio (WHR) to assess your risk of cardiovascular disease based on WHO guidelines.
Use this tool →Find out exactly how much water you should drink daily based on your weight, activity level and climate.
Use this tool →Calculate your ideal daily protein, fat and carbohydrate targets for weight loss, maintenance or muscle gain.
Use this tool →Calculate your maximum heart rate and personalized training zones for fat burn, cardio and peak performance.
Use this tool →Yes, completely free — every calculator on HydraFit.online is free to use, with no sign-up, subscription, or hidden fees, now or in the future.
No. Every calculation runs entirely in your browser using JavaScript. We never see, collect, transmit, or store the numbers you enter.
Absolutely — every tool on HydraFit is fully responsive and designed to work smoothly on mobile phones, tablets, and desktops.
No. Our tools provide general educational estimates based on established formulas. They are not a diagnosis and do not replace advice from a qualified healthcare professional. See our Medical Disclaimer for details.