Are these fitness calculators free?

Yes. The BMI, BMR and calorie calculators are completely free, need no sign-up, and run in your browser with instant results.

Which calculator should I use to lose weight?

Start with the calorie calculator (TDEE). It estimates how many calories you burn per day so you can eat below that for fat loss. Use BMR to find your safe minimum and BMI as a quick health screen.

How accurate are the calculators?

They use the Mifflin-St Jeor equation, one of the most accurate formulas. Real metabolism can vary ±15%, so treat the result as a starting point. The KeplerFit app recalibrates your true calorie needs from your actual weight trend over time.

Free Tools

Free Fitness Calculators

Work out your BMI, BMR and daily calorie needs in seconds — no sign-up, science-based formulas, instant results. Then let KeplerFit turn those numbers into a real plan.

🍽️ Calorie Calculator (TDEE) How many calories you burn and should eat per day, by goal. The number that drives fat loss or muscle gain. Open → 🔥 BMR Calculator Your basal metabolic rate — the calories you burn at rest. The floor you should not eat under. Open → ⚖️ BMI Calculator A quick height/weight health screen with healthy-range guidance. Open → 🍱 Macro Calculator Your daily protein, carbs and fat in grams — tailored to your goal. Open → 🥩 Protein Calculator How many grams of protein you need per day, by weight, activity and goal. Open → 🎯 Ideal Weight Calculator A realistic healthy-weight range for your height (Devine, Robinson, BMI). Open → 💧 Water Intake Calculator Your daily water target in litres and glasses, by weight, exercise and climate. Open → 🏋️ 1RM Calculator Your one-rep max (Epley + Brzycki) with a 60-95% training percentage table. Open →

Which calculator should I use?

Lose fat or gain muscle? → Calorie calculator (TDEE). Eat below it to cut, above it to gain.
Want to plan meals gram by gram? → Macro calculator. It splits your calories into protein, carbs and fat.
Building or protecting muscle? → Protein calculator for your g/kg target.
Wondering what you should weigh? → Ideal weight calculator — a realistic range, not one number.
Lifting weights? → 1RM calculator for your training percentages.
Worried you’re eating too little? → BMR. Don’t drop below it for long.
Just want a health snapshot? → BMI. And the water calculator keeps your hydration on track.

New to these terms? Read BMR vs TDEE vs BMI for a 5-minute plain-English explainer, or How many calories to lose weight for a step-by-step worked example.

From a number to a plan

A calculator gives you a starting number — but your real metabolism can be ±15% off any formula, and a number alone won’t tell you why your progress stalls. The KeplerFit app recalibrates your true calorie needs from your actual weight trend, then coaches you weekly on what to fix. Get the free app →

FAQ

Are these calculators free?

Yes — free, no sign-up, instant results in your browser.

Which one for weight loss?

The calorie calculator (TDEE). Eat below your TDEE to lose fat.

How accurate are they?

They use the Mifflin-St Jeor equation; expect ±15% individual variation. Treat results as a starting point.