Your Body.
Your Numbers.
Free health and fitness calculators — accurate, private, science-backed. No signup, no tracking, no fees.
- Runs entirely in your browser
- Your health data never leaves your device
- Peer-reviewed formulas, always free
Energy & Calories
How much fuel your body needs — and how to use it.
Body Composition
Understand what your body is made of — beyond the scale.
BMI & Ideal Weight
Check your BMI against WHO categories, see your healthy weight range, and compare four ideal weight formulas.
→Body Composition
Estimate body fat % with the U.S. Navy method and lean body mass with three formulas. See fat mass, lean mass, and FFMI.
→Waist-to-Hip Ratio
Assess cardiovascular risk with WHO waist-to-hip ratio categories.
→Nutrition
Dial in your protein, carbs, and fat.
Macro Split
Calculate daily protein, carbs, and fat targets from preset or custom ratios.
→Protein Intake
Find your daily protein target based on body weight, activity level, and fitness goal using ISSN guidelines.
→Water Intake
Calculate your daily water needs based on weight, activity level, and climate using IOM guidelines.
→Performance
Track and improve your strength and fitness.
One-Rep Max
Estimate your max lift with six proven formulas and get a training percentage table.
→Heart Rate Zones
Calculate your five training zones using Karvonen or max HR percentage with three formula options.
→Calories Burned
Estimate calories burned for 30+ activities using MET values from the Compendium of Physical Activities.
→Pace Calculator
Calculate running pace, finish time, or distance with per-mile and per-km split tables.
→VO2 Max
Estimate your aerobic fitness with four test methods and see your ACSM fitness classification.
→The Numbers Behind Your Health Goals
Whether you want to lose fat, build muscle, improve athletic performance, or simply understand what's happening in your body, everything starts with accurate numbers. NutriMath provides free, science-backed calculators that make those numbers clear — from your daily energy expenditure to your body composition.
Every calculator uses established, peer-reviewed formulas: the Mifflin-St Jeor equation for BMR (the most accurate for the general population), the Hodgdon-Beckett method for body fat (the U.S. military standard), and WHO thresholds for BMI and waist-to-hip risk categories. All calculations run entirely in your browser with no data sent to any server.
Start With Your Energy Balance
Your Total Daily Energy Expenditure (TDEE) is the number of calories your body burns in a day. It includes your resting metabolism, physical activity, and the energy cost of digesting food. Eating below your TDEE creates the caloric deficit needed for fat loss. Eating above it in a controlled surplus supports muscle growth. Without knowing your TDEE, any diet plan is guesswork.
Once you know your TDEE, the Calorie Target calculator helps you set a daily goal based on your desired rate of change — from a gentle 0.5 lb/week cut to a more aggressive 1.5 lb/week deficit. The Macro Split calculator then divides those calories into protein, carbohydrates, and fat targets in grams, with per-meal breakdowns.
Understand Your Body Composition
BMI is a useful first-pass screening tool, but it treats all weight equally — a 200-pound person with 12% body fat scores the same as one at 30%. For a more complete picture, the Body Composition calculator uses the U.S. Navy tape method to estimate your actual fat-to-lean ratio and tells you how much of your weight is muscle, bone, and organs — the metabolically active tissue that drives your calorie burn.
For cardiovascular risk assessment, the Waist-to-Hip Ratio calculator uses WHO thresholds to evaluate fat distribution — abdominal fat is more metabolically dangerous than fat stored in the hips and thighs, and WHR captures that distinction better than BMI.
Frequently Asked Questions
What is TDEE and why does it matter?
TDEE (Total Daily Energy Expenditure) is the total calories you burn per day — your basal metabolic rate plus all activity. It's the foundation of any diet plan. Eat below it to lose weight, above it to gain muscle, and at it to maintain. NutriMath uses the Mifflin-St Jeor equation, the most accurate formula for estimating TDEE.
How many calories should I eat to lose weight?
Eat fewer calories than your TDEE. A deficit of 500 calories per day produces roughly 1 pound of fat loss per week. Deficits over 1,000 calories daily risk muscle loss and metabolic slowdown. Use the Calorie Target calculator to set a safe target.
What are macros and how do I calculate them?
Macros are protein, carbohydrates, and fat — the three calorie sources in food. The right split depends on your goal: fat loss needs high protein to preserve muscle; muscle gain needs a calorie surplus with ample carbs. The Macro Split calculator gives gram-level targets.
What is a healthy BMI?
BMI between 18.5 and 24.9 is classified as normal weight. BMI is a useful screening tool but doesn't account for muscle mass — athletes often register as overweight despite low body fat. Body composition analysis gives a more complete picture.