Health & Fitness Calculators
Your Body.
Your Numbers.
Free fitness and nutrition calculators for weight loss, muscle gain, and performance — accurate, private, no signup required.
- Runs entirely in your browser
- Your health data never leaves your device
- Science-backed formulas, always free
BMI is a screening tool — not a measure of body composition or fitness
Full Calculator Suite Coming Soon
Free health and fitness calculators are on their way — TDEE, macros, calorie deficit, body fat, one-rep max, and more. No signup, no fees, ever.
Bookmark this page to be the first to use them.
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 is being built to provide the free, science-backed calculators that make those numbers clear — starting from the most foundational: your total daily energy expenditure.
TDEE is the number of calories your body burns in a day, accounting for both your resting metabolism and everything you do — walking, working out, even fidgeting. 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, diet and training advice is just guesswork.
TDEE, BMR, and Why Both Matter
Your Basal Metabolic Rate (BMR) is the calories your body burns at complete rest — just to maintain organ function, circulation, and body temperature. For most people, BMR accounts for 60–70% of total daily expenditure. TDEE multiplies BMR by an activity factor to arrive at your true daily burn.
NutriMath's calculators use the Mifflin-St Jeor equation, which consistently outperforms older formulas like Harris-Benedict in research comparing predicted versus measured metabolic rates. It takes your age, sex, height, and weight as inputs. The activity multiplier then adjusts for sedentary, lightly active, moderately active, very active, or extra active lifestyles.
Macros: Beyond Just Calories
Once you know your TDEE and calorie target, the next question is how to split those calories between protein, carbohydrates, and fat. The right macro ratio depends on your goal:
- Fat loss: Higher protein (0.8–1g per pound of bodyweight) preserves muscle during a deficit. Carbs and fat fill the remaining calories based on preference.
- Muscle gain: Protein stays high; carbohydrates are typically increased to fuel training and recovery. A moderate surplus of 200–300 calories above TDEE minimizes fat gain.
- Maintenance: More flexible ratios work — the priority is hitting your calorie target and adequate protein.
NutriMath's macro calculator builds on your TDEE to give you gram-level targets for each macronutrient, tailored to your goal and body weight.
Body Composition: What BMI Doesn't Tell You
BMI is useful as a quick population-level screening tool, but it has real limitations for individuals. A 200-pound person who is 5'10" with 15% body fat will have the same BMI as a 200-pound person at 30% body fat — but their health profiles are completely different. NutriMath will offer body fat calculators using the US Navy method (waist, neck, and height measurements) that give a more accurate picture of body composition than BMI alone.
Understanding your body fat percentage also clarifies your true lean mass — the muscle, bone, and organ tissue that drives your BMR. Knowing that number helps you set more accurate protein targets and track the right outcome when you're dieting: losing fat while maintaining lean mass, not just watching the scale go down.
Performance: Strength and Cardio Tools
For athletes and regular gym-goers, NutriMath will include performance calculators alongside the nutrition tools. The one-rep max calculator estimates your maximum lift from any working set, using the Epley or Brzycki formula. The VO2 max estimator uses running performance data. Heart rate zone calculators help you train at the right intensity for fat burn, aerobic base building, or threshold work.
These tools matter because training and nutrition are inseparable. Your calorie needs change on heavy training days versus rest days. Protein requirements scale with training volume. Knowing both sides of the equation lets you fuel and recover with precision.
Accurate, Private, Always Free
Every calculator on NutriMath runs entirely in your browser. Your weight, height, age, and health data never leave your device — there are no servers, no accounts, and nothing stored anywhere. Calculations use established, peer-reviewed formulas that you can verify independently. NutriMath is launching soon with a full suite of health, nutrition, and fitness tools. Bookmark this page and check back.
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. NutriMath's calorie deficit calculator will set a safe target based on your TDEE and timeline.
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 for training fuel. NutriMath's macro calculator gives you gram-level targets based on your TDEE and objective.
What is a healthy BMI?
BMI between 18.5 and 24.9 is classified as normal weight. Below 18.5 is underweight; 25–29.9 is overweight; 30 and above is obese. BMI is a useful screening tool but doesn't account for muscle mass — athletes often register as overweight despite low body fat. Body fat percentage gives a more complete picture.