BMR Calculator
BMR Calculator estimates your Basal Metabolic Rate — the calories your body burns at complete rest just to stay alive. Enter your age, sex, height, and weight to see three respected formulas side by side, add an optional body-fat percentage for a body-composition estimate, and get your answer instantly. No sign-up — your details never leave your browser.
What is the BMR Calculator?
The BMR Calculator estimates your Basal Metabolic Rate — the calories your body burns at complete rest just to stay alive, powering your heart, brain, breathing, and other vital functions. Instead of handing you a single number from one equation, it runs three respected formulas at once — Mifflin-St Jeor, Harris-Benedict, and Katch-McArdle — so you see a realistic range rather than false precision. Enter a few details and all three estimates appear instantly, entirely in your browser.
How to use it
- Choose Metric (kg, cm) or Imperial (lb, ft/in) — the tool converts your input internally so every formula runs in metric.
- Enter your age and select your sex; both change the height-based formulas.
- Enter your height and weight in the unit boxes shown.
- Optionally add your body-fat percentage to unlock the Katch-McArdle estimate, which is based on lean body mass.
- Read each formula's BMR side by side. Everything recalculates the moment you change a value, so you get your answer and close the tab.
The three formulas behind it
All three equations return calories per day. Mifflin-St Jeor (1990) is the default and most recommended predictor for the general population:
Men: BMR = 10 x weight(kg) + 6.25 x height(cm) - 5 x age + 5
Women: BMR = 10 x weight(kg) + 6.25 x height(cm) - 5 x age - 161
Revised Harris-Benedict is the classic older formula and usually reads a little higher:
Men: BMR = 88.362 + 13.397 x kg + 4.799 x cm - 5.677 x age
Women: BMR = 447.593 + 9.247 x kg + 3.098 x cm - 4.330 x age
Katch-McArdle is the only one driven by body composition rather than height and age, which makes it the most accurate when you know a reliable body-fat percentage:
LBM = weight(kg) x (1 - bodyFat% / 100)
BMR = 370 + 21.6 x LBM
BMR vs TDEE — what is the difference?
Your BMR is your resting baseline: the energy you would burn if you stayed in bed all day. Your TDEE (Total Daily Energy Expenditure) is what you actually burn across a whole day, found by multiplying your BMR by an activity factor that adds the energy you spend moving, working, and exercising. BMR is the starting point; TDEE is the number you use to plan how much to eat. Once you have your BMR here, our TDEE Calculator turns it into your maintenance calories.
Worked examples
Take a 30-year-old man, 180 cm, 80 kg. His Mifflin-St Jeor BMR is 10×80 + 6.25×180 − 5×30 + 5 = 1,780 kcal/day, and his Harris-Benedict BMR is about 1,856 kcal/day. If his body fat is 15%, his lean mass is 68 kg and the Katch-McArdle estimate is about 1,839 kcal/day. A 30-year-old woman, 165 cm, 60 kg has a Mifflin-St Jeor BMR near 1,320 kcal/day and a Harris-Benedict BMR near 1,394 kcal/day, showing how sex and size move the numbers.
Common use cases
- Finding your resting calorie baseline before building a diet plan.
- Comparing formula results to get an honest range instead of one figure.
- Getting a body-composition-aware estimate when you know your body fat.
- Sanity-checking the BMR a fitness app reported.
- Pairing your BMR with a TDEE or calorie tool to set a daily target.
Why use this one
Most BMR calculators give you a single formula and call it done. This one shows all three equations together, supports metric and imperial with on-page conversion, accepts an optional body-fat percentage for the Katch-McArdle method, and updates instantly as you type. It is fully private: every calculation runs in your browser, so your age, weight, and body-fat figures are never uploaded, stored, or shared.
Results are estimates for general informational and educational purposes only and are not medical, nutritional, or fitness advice. Calorie prediction formulas are population averages and individual needs vary. Consult a qualified doctor or registered dietitian before changing your diet, especially if you have a health condition, are pregnant, or are under 18.
Frequently asked questions
What is BMR?
BMR stands for Basal Metabolic Rate: the number of calories your body burns at complete rest just to keep you alive, powering your heart, brain, breathing, and other vital functions. It is measured as if you were lying still and fasted, so it does not include any movement, digestion, or exercise. BMR typically accounts for the largest single share of the calories you burn each day.
What is the difference between BMR and TDEE?
BMR is the calories you burn at rest, while TDEE (Total Daily Energy Expenditure) is the total you burn over a full day. TDEE takes your BMR and multiplies it by an activity factor to add the energy you spend moving, working, and exercising. In short, BMR is your baseline and TDEE is your real-world daily total, which is why TDEE is the number you use to plan how much to eat.
Which BMR formula is most accurate?
For most people without a known body-fat percentage, the Mifflin-St Jeor equation is considered the most accurate predictor and is the default here. If you know a reliable body-fat percentage, the Katch-McArdle equation is often more accurate because it is based on lean body mass rather than averages, especially for very lean or muscular people. Harris-Benedict is the classic older formula and usually reads a little higher.
Do I need my body fat percentage to use this calculator?
No. The Mifflin-St Jeor and Harris-Benedict results only need your sex, age, height, and weight, so you can get a BMR estimate without any body-fat figure. Body fat is optional and only unlocks the Katch-McArdle equation, which adds a more body-composition-aware estimate when you have a measurement to enter.
Why do the three formulas give different numbers?
Each equation was built from a different study population and uses slightly different inputs, so they will rarely match exactly. Mifflin-St Jeor and Harris-Benedict both use height, weight, age, and sex but with different coefficients, while Katch-McArdle ignores those and uses lean body mass instead. Seeing all three together gives you a realistic range rather than a single false-precision number.