Free fitness calculators
that actually help
Calculate your TDEE, macros, BMR, body fat, and more — all in one place. No sign-up, no nonsense.
TDEE Calculator
Total Daily Energy Expenditure — the foundation of any diet or fitness plan. Find out exactly how many calories your body burns per day.
BMR Calculator
Basal Metabolic Rate — calories burned at complete rest using Mifflin-St Jeor & Harris-Benedict.
Macros Calculator
Get your optimal protein, carbs, and fat targets for your cut, bulk, or recomp goal.
Body Fat Calculator
Estimate body fat percentage using the US Navy method and BMI-based calculation.
Ideal Weight Calculator
See your ideal weight range using Robinson, Miller, Devine, and Hamwi formulas.
One Rep Max Calculator
Calculate your 1RM for any lift using Epley, Brzycki, and Lombardi formulas.
Calories Burned Calculator
Find out how many calories you burn during 40+ activities using MET values.
Why use MyBodyMath?
Every calculator on MyBodyMath uses peer-reviewed, clinically validated formulas — the same ones used by registered dietitians and sports scientists. We show you which formula we're using and why, so you can make informed decisions about your nutrition and training.
Unlike apps that require sign-ups or subscriptions, MyBodyMath is free, private, and works instantly. Your results are calculated in your browser — nothing is stored on our servers.
Frequently asked questions
TDEE (Total Daily Energy Expenditure) is the total number of calories you burn in a day, including your basal metabolism, physical activity, and the energy used to digest food. It's the single most important number for weight management — eat below it to lose weight, above it to gain, or at it to maintain. Every other nutrition calculation flows from your TDEE.
Our calculators use the most accurate published formulas available. The Mifflin-St Jeor equation for BMR, for example, has been shown in studies to be accurate within 10% for most people. However, all formulas are population-based estimates — your actual metabolism may vary by 5–20% depending on genetics, hormones, muscle mass, and other factors. Treat these numbers as a starting point and adjust based on real results over 2–4 weeks.
BMR (Basal Metabolic Rate) is the calories your body burns at complete rest — just to keep your organs functioning. TDEE is BMR multiplied by an activity factor, which accounts for all the extra energy you burn through movement, exercise, and digesting food. In practice, TDEE is the number you use for diet planning; BMR is mainly useful for understanding what portion of your calorie needs comes from baseline metabolism.
To lose weight, eat in a calorie deficit below your TDEE. A 500-calorie daily deficit typically produces about 1 lb (0.45 kg) of weight loss per week. Most experts recommend a deficit no larger than 25% of TDEE to preserve muscle mass and avoid hormonal disruption. Use our TDEE calculator to find your maintenance calories, then subtract 300–500 calories for a moderate, sustainable cut.