Calculators for Body Fat, Nutrition & Fitness
FatCalc offers a comprehensive suite of free calculators to help you understand your body and make informed health decisions. Whether you're tracking body composition, planning your nutrition, assessing cardiovascular fitness, or setting training goals, our tools are built on validated formulas and research-backed methods to provide accurate, personalized estimates. Click any calculator link below to get started.
Calculate Your Calorie Deficit for Realistic Weight Loss What would be a realistic weight loss goal for you? Find out and discover how long it would take for you to reach it.
Body Fat Calculator Discover your ideal weight for a healthy body fat percentage with this free body fat calculator.
Calculate Your Daily Calories and Macros to Reach Your Goal Weight Use this calorie calculator to achieve and maintain your weight loss or weight gain goal within a realistic time frame. It calculates the daily calories and macros you need to reach your desired weight.
Muscle Mass Calculator Estimate your skeletal muscle mass percentage with this free calculator. Compare your results to research-based averages by age and sex.
Maximum Fat Loss Calculator Determines the amount of calories needed to optimize the reduction of body fat while preserving muscle mass.
Macro Calculator Calculates your macronutrient requirements based on your calorie intake and diet type. Track your macros instead of counting calories.
Protein Calculator Calculate your daily protein needs based on weight, activity level, and fitness goals. Personalized recommendations from 0.8–2.2 g/kg body weight.
Creatine Dosage Calculator Calculate your optimal creatine dosage based on body weight and supplementation phase level using ISSN guidelines.
RMR & BMR Calculator Calculate your resting metabolic rate with 3 science-backed formulas. Compare your RMR against data from 12,000 adults. Free, accurate, with detailed explanations.
TDEE Calculator for All Ages This calculator can determine your total daily energy expenditure (TDEE) and is accurate for all age groups, including young children.
A Body Shape Index (ABSI) Calculator Calculates your ABSI; a body shape index of your body and estimates your mortality risk. A pear shaped body is healthier than an apple shaped body. Find out why.
Ideal Body Weight Calculator Calculate your ideal body weight using four validated formulas (Devine, Robinson, Miller, Hamwi). Get a range of estimates based on height and sex, with optional frame size adjustments and BMI-based healthy weight ranges for comparison.
Waist-to-Hip Ratio Calculator Calculates your Waist-to-Hip ratio and compares your risk against a chart formulated by the WHO.
Waist-to-Height Ratio Calculator Calculate your waist-to-height ratio (WHtR) to assess health risk linked to abdominal fat. A simple, evidence-based alternative to BMI.
Calories Burned Calculator Want to burn fat calories? Use this calculator to plan your physical activities to reach your goal.
BMI Calculator for Children and Adults Calculates Body Mass Index designed for both children and adults.
Intermittent Fasting Window Calculator Calculate your eating and fasting windows for popular IF protocols. See when you enter fat burning, ketosis, and autophagy states.
Hydration Calculator Calculate your personalized daily water intake based on weight, exercise, and climate. Go beyond "8 glasses a day" with science-backed hydration recommendations.
Heart Rate Zone Calculator Calculate your personal heart rate training zones using the Karvonen method. Choose from Tanaka, Fox, or Gulati formulas to find your optimal workout intensity.
One Rep Max (1RM) Calculator Calculate your one rep max using 7 validated formulas: Epley, Brzycki, Wathen & more. Get personalized training loads from 55-100% 1RM for any lift.
VO2 Max Calculator Estimate your VO2 Max using multiple methods: resting heart rate, Rockport 1-mile walk, Cooper 12-minute run, 1.5-mile run test, race time prediction, or YMCA step test. Compare your cardiovascular fitness against ACSM age-specific norms.
Body Recomposition Calculator Calculate your potential for simultaneous fat loss and muscle gain. Get personalized calorie and protein targets based on your training status and body composition.
Caffeine Calculator Calculate how caffeine affects your body based on dose, weight, and metabolism. See when caffeine peaks, how long until it clears, and its impact on sleep.
Longevity Calculator Assess your daily habits across nutrition, exercise, sleep, stress, and more to get a comprehensive longevity score with personalized recommendations.
Measurement Conversions Quick conversion of US and Metric measurements ideal for household use.
Understanding Your Body Composition
If you’re trying to lose weight, it’s important to know what that weight is made of—mainly fat, stored as adipose tissue.
Adipose tissue is made up of cells called adipocytes, each containing a big fat droplet. This storage part of the cell, known as a 'lipid droplet,' is mostly composed of triglycerides—three fatty acids linked to glycerol, which is a type of alcohol found in fats. When you lose weight, these triglycerides are what your body uses up.
Body composition includes not just fat but also lean mass, such as muscle, bones, organs, and water. The balance between fat mass and lean mass tells you far more about health than body weight alone. Tracking body fat percentage and muscle mass offers better insights than simply watching the scale.
Metabolic Rate and Energy Balance
Your body burns calories even at rest, called Basal Metabolic Rate (BMR) or the closely related Resting Metabolic Rate (RMR). These numbers show the amount of calories needed for basic life functions, such as breathing and cell repair.
Your Total Daily Energy Expenditure (TDEE) is the amount of calories you burn each day from life functions, movement, exercising, and even digesting food. Tracking your TDEE makes it easier to reach your goals, whether that’s losing fat, maintaining your current weight, or building muscle. Creating a small calorie deficit (eating fewer calories than your TDEE) supports fat loss, while eating more than your TDEE with resistance training can help you gain muscle.
Nutrition and Macronutrients
Calories only measure energy. The three main macronutrients—protein, carbohydrates, and fats—have unique roles. Protein builds and repairs muscle, especially during calorie deficits or intense training. Carbohydrates fuel high-intensity activity, and fats produce hormones, aid nutrient absorption, and keep cells healthy.
Don’t forget hydration. Water is essential for almost every process in your body. How much you need depends on your size, activity, and climate. Staying hydrated boosts exercise performance, cognitive function, and overall well-being.
Cardiovascular Fitness
Your cardiovascular system's efficiency is measured in several ways. VO₂ max, the maximum amount of oxygen your body can use during intense exercise, is considered the gold standard of aerobic (using oxygen) fitness. Higher VO₂ max values generally mean better endurance and a lower risk of cardiovascular disease.
Training in different heart rate zones and specific heart rate ranges offers unique benefits. Lower heart rate zones boost aerobic (oxygen-using activities like jogging) endurance and fat burning, while higher zones enhance anaerobic (short-burst, intense activities) power and peak performance. You can find your heart rate zones using your maximum (fastest possible) and resting (slowest, such as when you are relaxed) heart rates, helping you personalize your workouts to fit your goals.
Strength and Resistance Training
For those focused on building strength, identifying your one-rep max (1RM), the maximum weight you can lift a single time, guides your training. You then use specific percentages of your 1RM to set training loads: lower percentages for endurance (lifting lighter weights for more repetitions), moderate for hypertrophy (muscle growth), and higher for increasing maximum strength.
You can lose fat and build muscle at the same time, especially if you’re just starting, returning after a break, or have higher body fat to begin with.
Common Misconceptions About Fat Loss
You might have heard that fat turns into muscle, but that’s just a myth. Fat and muscle are totally separate. Still, you can lose fat and gain muscle on your way to a toned look.
Another myth: you can spot-reduce fat with targeted exercises. In reality, genetics and hormones decide where you lose fat. All targeted moves do is build the muscle underneath, not shrink the fat in that area.
Crash diets and big calorie cuts may seem like shortcuts for weight loss, but they usually backfire. They cause quick weight loss at first, but are hard to stick with and often unhealthy. You risk losing muscle, missing nutrients, and slowing your metabolism, which can make it hard to keep weight off.
Longevity and Lifestyle Factors
Health is more than fitness or body composition. Eating well, moving often, sleeping enough, handling stress, and maintaining strong relationships all add up to a longer, healthier life. Even small, steady changes really do help.