Free Health & Fitness Calculators

Why Use Health Calculators?

Understanding your body's numbers helps you make informed decisions about nutrition, exercise, and wellness. Our calculators use medically validated formulas to give you personalized insights:

• Personalized nutrition — Know exactly how many calories and macros your body needs
• Smarter workouts — Train in the right heart rate zone for your fitness goals
• Track progress — Monitor body composition changes over time
• Stay hydrated — Get a science-based daily water target
• 100% private — All calculations run in your browser, no data sent anywhere

About Our Formulas

We use peer-reviewed, clinically validated equations: the Mifflin-St Jeor equation for BMR (recognized as the most accurate by the American Dietetic Association), the US Navy body fat formula, the Karvonen formula for heart rate zones, and MET-based calculations from the Compendium of Physical Activities for calorie burn estimates.

Health & Fitness Tips

Start with Your TDEE

Your Total Daily Energy Expenditure (TDEE) is the foundation of any diet plan. Use our Calorie Calculator to find your TDEE, then adjust based on your goal: subtract 500 calories/day to lose ~1 lb/week, or add 300-500 to build muscle.

Protein Is Key

Whether you're losing fat or building muscle, protein is essential. The Macro Calculator helps you find the right protein-carb-fat balance for your specific goals. Most active adults need 0.7-1g of protein per pound of body weight.

Don't Forget Hydration

Even mild dehydration can reduce exercise performance by 10-20%. Use the Water Intake Calculator to get your personalized daily target based on your weight and activity level.

Train Smarter, Not Harder

Heart rate zone training ensures you're exercising at the right intensity. Zone 2 (60-70% max HR) burns fat efficiently, while Zone 4-5 builds peak fitness. Use the Heart Rate Zone Calculator to find your personal zones.

Understanding Your Body Metrics

BMR vs TDEE: What's the Difference?

Your Basal Metabolic Rate (BMR) is the number of calories your body burns at complete rest — just to keep your heart beating, lungs breathing, and organs functioning. It typically accounts for 60–75% of your total daily calorie burn. Your Total Daily Energy Expenditure (TDEE) adds activity on top of BMR using an activity multiplier:

• Sedentary (desk job, little exercise): BMR × 1.2
• Lightly active (light exercise 1–3 days/week): BMR × 1.375
• Moderately active (moderate exercise 3–5 days/week): BMR × 1.55
• Very active (hard exercise 6–7 days/week): BMR × 1.725
• Extremely active (athlete, physical job + training): BMR × 1.9

The Calorie Calculator computes both BMR and TDEE using the Mifflin-St Jeor equation, which the American Dietetic Association considers the most accurate for healthy adults.

Body Fat Percentage: What the Numbers Mean

Body fat percentage is a more useful indicator of health than weight alone, because it distinguishes between fat mass and lean mass (muscle, bone, water). General guidelines for adults:

• Essential fat: 2–5% (men), 10–13% (women) — minimum for basic physiological function
• Athletes: 6–13% (men), 14–20% (women)
• Fitness: 14–17% (men), 21–24% (women)
• Average: 18–24% (men), 25–31% (women)
• Obese: 25%+ (men), 32%+ (women)

The Body Fat Calculator uses the US Navy method, which requires only waist, neck, and height measurements and has been validated to within 3–4% of DEXA scan results for most adults.

Heart Rate Zones Explained

Training in specific heart rate zones targets different fitness adaptations. Your maximum heart rate (MHR) is estimated as 220 minus your age, and the five zones are:

• Zone 1 (50–60% MHR): Warm-up and recovery. Very light effort, sustainable for hours.
• Zone 2 (60–70% MHR): Fat burning and endurance base. Conversational pace. Most beneficial for general health.
• Zone 3 (70–80% MHR): Aerobic fitness. Moderate effort, improving cardiovascular efficiency.
• Zone 4 (80–90% MHR): Anaerobic threshold. Hard effort, improves speed and lactate tolerance.
• Zone 5 (90–100% MHR): Maximum effort. Sprint intervals only, sustainable for 30–90 seconds.

The Heart Rate Zone Calculator uses the Karvonen formula, which factors in your resting heart rate for more personalized zone boundaries.

📚 All Health & Fitness Guides

Dive deeper into the science behind each calculator with our comprehensive guides written by health and fitness researchers.

• Nutrition & Calorie Guide — Calories, TDEE, macronutrients, and building a sustainable nutrition plan
• Fitness & Exercise Guide — Heart rate zones, MET values, workout planning, and the 80/20 principle
• Body Composition Guide — Body fat, ideal weight formulas, BMI limitations, and improvement strategies
• Hydration Guide — Daily water needs, electrolytes, signs of dehydration, and hydration during exercise
• Sleep & Recovery Guide — Sleep cycles, circadian rhythm, sleep hygiene, and the link between sleep and fitness
• Heart Rate Zones Guide — Zone training explained, calculating zones, and training plans for each goal
• Pregnancy Health Guide — Trimester milestones, nutrition needs, safe exercise, and weight gain guidelines
• Strength Training Guide — Progressive overload, rep ranges, compound movements, and program design
• Mental Health & Exercise — How exercise reduces anxiety and depression, and evidence-based recommendations

View all fitness guides →