By Ziv Shay | Updated April 2026
BMI, TDEE, calories, ideal weight, body fat, macros & more — all free
Total Daily Energy Expenditure — how many calories you burn per day
Measure in cm using a flexible tape
Ever wonder how many burpees it takes to burn off that pizza?
Mind-blowing facts about what your body does every single day
Understanding your body composition and caloric needs is the foundation of any effective fitness plan. Whether your goal is losing fat, building muscle, or improving athletic performance, the numbers matter. Your Total Daily Energy Expenditure (TDEE) determines how many calories you burn in a 24-hour period, your BMI provides a general health screening metric, and your body fat percentage reveals the ratio of fat to lean tissue that truly defines your physique and metabolic health.
The fitness calculator above combines multiple evidence-based formulas used by sports scientists and registered dietitians. The Mifflin-St Jeor equation, considered the most accurate for estimating Basal Metabolic Rate (BMR) by the Academy of Nutrition and Dietetics, forms the core of the calorie calculations. Activity multipliers from exercise physiology research adjust your BMR to reflect real-world energy expenditure based on your lifestyle and training frequency.
Body Mass Index divides your weight in kilograms by your height in meters squared. The standard categories are: underweight (below 18.5), normal weight (18.5-24.9), overweight (25-29.9), and obese (30+). While BMI is useful for population-level health screening and insurance risk assessment, it has significant limitations for individuals. BMI cannot distinguish between muscle and fat, meaning a muscular athlete with 10% body fat could be classified as "overweight." For personal fitness assessment, body fat percentage and waist-to-hip ratio are more informative metrics.
Fat loss: Create a caloric deficit of 300-500 calories below your TDEE for sustainable fat loss of 0.5-1 pound per week. Aggressive deficits exceeding 750 calories lead to muscle loss, metabolic adaptation, and are difficult to maintain long-term. Aim for 0.7-1.0 grams of protein per pound of bodyweight during a deficit to preserve muscle mass.
Muscle gain: A caloric surplus of 200-350 calories above TDEE supports muscle growth while minimizing fat gain. Beginners can build muscle in a slight surplus or even at maintenance calories. Advanced lifters need a more precise surplus. Prioritize 1.0-1.2 grams of protein per pound of bodyweight and strength training 3-5 days per week.
Body recomposition: Eating at or near maintenance calories while training with progressive overload allows you to simultaneously lose fat and gain muscle, especially if you are a beginner, returning after a layoff, or carrying significant body fat. This approach is slower but produces lasting results without the discomfort of extreme dieting.
Macronutrients (protein, carbohydrates, and fats) each play distinct roles in body composition and performance. Protein (4 calories per gram) supports muscle repair and satiety. Most fitness goals require 0.7-1.2g per pound of bodyweight. Carbohydrates (4 calories per gram) fuel high-intensity exercise and brain function. Athletes and heavy trainers need 2-3g per pound; those in sedentary jobs may do well with 1-1.5g per pound. Fats (9 calories per gram) support hormone production and nutrient absorption. Minimum intake should be 0.3-0.4g per pound of bodyweight, with 25-35% of total calories from fat being a healthy range.
TDEE calculators provide an estimate within 10-15% of your actual caloric needs. They are an excellent starting point but require real-world adjustment. Track your calorie intake and body weight for 2-3 weeks. If your weight stays stable, you have found your true maintenance calories. If you are gaining weight, reduce intake by 100-200 calories. If losing, increase by the same amount. Recalculate every 10-15 pounds of weight change.
For men, essential fat is 2-5%, athletic range is 6-13%, fitness range is 14-17%, and acceptable is 18-24%. For women, essential fat is 10-13%, athletic range is 14-20%, fitness range is 21-24%, and acceptable is 25-31%. Visible abdominal definition typically appears around 10-14% for men and 16-20% for women. Maintaining extremely low body fat (below 6% men, below 14% women) long-term can negatively impact hormonal health and immune function.
Start with your TDEE and subtract 300-500 calories. For example, if your TDEE is 2,400 calories, aim for 1,900-2,100 calories daily. This creates a deficit that results in approximately 0.5-1 pound of fat loss per week. Do not go below 1,200 calories (women) or 1,500 calories (men) without medical supervision, as very low calorie diets risk nutrient deficiencies, muscle loss, and metabolic slowdown.
Research consistently shows that 0.7-1.0 grams of protein per pound of bodyweight per day is sufficient for maximizing muscle protein synthesis. Going above 1.2g per pound provides no additional muscle-building benefit but may help with satiety during a fat loss phase. Space protein intake across 3-5 meals of 25-40 grams each for optimal absorption and muscle recovery.
Body fat percentage is more informative for individual health and fitness assessment. Two people with identical BMIs can have vastly different body compositions: one might be lean and muscular while the other carries excess visceral fat. However, BMI remains useful as a quick screening tool and is used by insurance companies and public health organizations because it requires only height and weight to calculate.
Affordable equipment to level up your workouts
As an affiliate, we may earn from qualifying purchases
The average American could save $5,000/year by optimizing their tax strategy. Try our tax calculator →
Paying an extra $100/month on your mortgage saves $30,000+ in interest over the life of the loan. Calculate your savings →
Starting to invest at 25 vs 35 can mean $500,000+ more at retirement thanks to compound interest. See the difference →
Refinancing student loans at a 2% lower rate saves $10,000–$20,000 over the loan term. Check your rate →
AI How To Invest provides 175+ free financial calculators and tools to help you make smarter money decisions. From mortgage and retirement planning to debt payoff strategies and investment analysis, our tools are designed to be fast, accurate, and easy to use. All calculator data stays in your browser — we never sell your personal information.
Trusted by tens of thousands of users for financial planning, tax optimization, and investment research. Learn more about us →
© 2024–1970 AIHowToInvest.com — 175+ Free Financial Tools | About | Contact | Privacy | Terms | Disclaimer
