Fitness
BMR Calculator
Basal metabolic rate via the Mifflin–St Jeor equation.
Free to use — no sign-up or login.
BMR
kcal/day
Amortization schedule
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BMR is an estimate of calories used at complete rest — breathing, circulation, temperature. This calculator uses Mifflin–St Jeor with weight, height, age, and sex. Treat the result as a resting-energy screen, not a meal plan or a medical verdict.
The arithmetic and a slider demo live in How to Calculate BMR. For daily calories that include movement, the Calorie Calculator estimates TDEE. The BMI Calculator is a different screening ratio; composition estimates live on the Body Fat Calculator.
What is BMR?
Basal metabolic rate, or BMR, is the energy your body spends just to stay alive when you are not moving, digesting, or fighting the cold. The heart still pumps, lungs still cycle air, and cells still repair. That quiet baseline is most of a typical day's burn — often around two-thirds of total energy — before walking or training add their share.
It is a prediction here, not a hood measurement. A laboratory BMR is taken under strict rules: fasting, a thermoneutral room, and complete rest. This calculator estimates it from weight, height, age, and sex with the Mifflin–St Jeor equation, which dietetics reviews (including the Academy of Nutrition and Dietetics' journal) have often preferred for healthy adults over older Harris–Benedict versions. NIH weight-management materials treat resting energy as one input to daily needs, not a meal plan.
BMR is not “calories you should eat.” Eating only at BMR while you live a normal day would underfuel most people. Resting metabolic rate (RMR) is a close cousin with slightly looser rest rules; total daily energy expenditure (TDEE) folds in movement. If the number looks odd, look at activity, muscle, or a clinician — not a crash diet off one estimate.
BMR vs RMR vs TDEE
Clinics and apps mix these three labels. BMR is the strict rest floor. RMR is resting energy under slightly looser conditions — same ballpark, usually a bit higher. TDEE is the day's total: rest plus movement plus the cost of eating. This calculator reports BMR only. The table is a map, not a lab report. For a daily target that includes activity, use the Calorie Calculator; How to Calculate BMR stays on the Mifflin arithmetic rather than repeating a full how-to here.
| Measure | What it estimates | Typical conditions | Includes activity |
|---|---|---|---|
| BMR | Calories for vital functions at complete rest | Strict rest, often fasting, thermoneutral | No |
| RMR | Resting calories with slightly looser rest rules | Clinic or “rested” measurement | No |
| TDEE | Daily energy including movement and daily living | Planning (BMR × activity factor) | Yes |
Factors That Affect BMR
Age pulls BMR down over adult life, mainly because people tend to lose muscle and gain fat, and because the formula's age term is a population shortcut for that drift. A 70-year-old and a 25-year-old at the same weight and height will not get the same Mifflin number; the older adult's estimate is lower even before lifestyle shows up. Sex, or gender as many apps label the same male/female constant, is in the equation because the original samples split that way and because, on average, men carry more fat-free mass. It is not a hormone panel. People outside that binary, or on gender-affirming hormones, should treat the two constants as crude brackets, not as identity tests, and talk with a clinician who knows their labs.
Muscle mass is the big tissue story. Muscle burns more at rest than an equal weight of fat, which is why a strength-trained adult can out-burn a same-weight peer on the couch, and why the BMI Calculator can look “overweight” while resting energy is high. Genetics set a fairly tight personal range; you do not get to pick a celebrity metabolism. Hormones matter too: thyroid hormone, sex hormones, and cortisol all nudge resting burn, and so do some medicines. Illness, crash dieting, and sleep loss can drop expenditure in ways no age-sex equation sees. This page cannot measure any of that. If BMR looks wildly off, or you have a known endocrine condition, use the number as a flag for a clinician, not a diagnosis.
BMR Calculation Formulas
This calculator uses Mifflin–St Jeor (1990), the equation printed beside the form: males BMR = 10w + 6.25h − 5a + 5; females BMR = 10w + 6.25h − 5a − 161, with w in kilograms, h in centimeters, and a in years. Use it when you have those four inputs and no trustworthy lean-mass figure — the usual adult case. How to Calculate BMR walks through a numeric example; this section is only which formula is which.
Harris–Benedict is older (Harris and Benedict, 1918/1919). In the same units, the original equations are males 66.473 + 13.752w + 5.003h − 6.755a and females 655.096 + 9.563w + 1.850h − 4.676a. A 1984 revision (Roza and Shizgal) changes the constants again. Either version will disagree with this page. Textbooks still print Harris–Benedict; dietetics reviews have generally found Mifflin closer to measured resting energy in healthy adults.
Katch–McArdle ignores sex and age and uses fat-free mass: BMR = 370 + 21.6 × FFM (kg), where FFM is lean mass. Use it when you trust a body-fat or lean-mass estimate more than the age–sex tables — often athletes. This widget does not accept body fat. The Body Fat Calculator and Lean Body Mass Calculator are still estimates; you can apply Katch–McArdle by hand from them. None of the three families is a metabolic cart, and none is medical advice.
Worked example: 70 kg, 175 cm, age 30
Metric male, 70 kg, 175 cm, age 30: BMR = 10×70 + 6.25×175 − 5×30 + 5 = 700 + 1093.75 − 150 + 5 = 1648.75 kcal/day.
\[ BMR=10(70)+6.25(175)-5(30)+5=1648.75 \]
Frequently asked questions
What's the difference between BMR and RMR?
BMR is basal metabolic rate: calories at complete rest under strict lab-style conditions — typically fasting, a thermoneutral room, and no recent movement. RMR is resting metabolic rate: the same idea measured with slightly looser rest rules, so it usually comes out a little higher. In everyday talk people mix the names; many clinic “resting energy” tests are closer to RMR. This calculator predicts BMR with Mifflin–St Jeor from weight, height, age, and sex. It does not run a metabolic cart. For daily planning you still need activity on top (TDEE), which is why the Calorie Calculator exists. Neither number is a diagnosis or a diet prescription — talk with a clinician or registered dietitian if you need a care plan.
How can I increase my BMR?
BMR mostly tracks the tissue you carry and your size. Building or keeping muscle raises resting burn more than fat does, so strength work over months is the lever with the best evidence — not a supplement or a “metabolism hack.” Age and sex sit in the formula because they correlate with lean mass and hormones; you cannot type those away. Crash dieting can lower expenditure; eating enough protein and training is the usual path. Sleep, thyroid disease, and some medications also move resting energy, which this page cannot see. Treat the number as a screen. If it looks oddly low or high, or you want a change in body composition, that is a talk with a clinician or dietitian, not a promise from a calculator.
Is this the Harris–Benedict equation?
No. This page uses Mifflin–St Jeor (1990): 10w + 6.25h − 5a + 5 for males and −161 for females, with w in kilograms, h in centimeters, and a in years. Harris–Benedict is an older pair of equations (1918/1919, later revised) that also uses weight, height, age, and sex but different coefficients, so the kcal/day will not match. Reviews in the Academy of Nutrition and Dietetics' journal have generally favored Mifflin–St Jeor over Harris–Benedict for healthy adults. If a textbook or app still prints Harris–Benedict, that is a different estimate, not a bug here. How to Calculate BMR walks through the Mifflin arithmetic; the formulas section on this page compares all three families.
Does BMR include exercise?
No. BMR is rest only — the energy to keep organs running when you are not moving. Walking, training, and fidgeting sit on top of it. The usual planning stack is TDEE ≈ BMR × an activity factor; a calorie deficit is then a gap below that TDEE, not below BMR. Eating only your BMR while you live a normal day would underfuel most people. Use the Calorie Calculator when you want a daily target that includes activity. This page will not add exercise for you, and the activity multipliers elsewhere are coarse labels, not a heart-rate measurement. Treat both numbers as planning estimates, not as a prescription to eat or train a certain way without a clinician in the loop.
When should I use Katch–McArdle instead?
Katch–McArdle estimates resting energy from fat-free mass: 370 + 21.6 × lean mass in kilograms. Use it when you have a decent lean-mass or body-fat figure and you care that muscle is not treated as mystery weight — athletes and people with more lean mass than the age/sex tables assume. This calculator does not take body fat; it uses Mifflin–St Jeor. You can estimate composition with the Body Fat Calculator or Lean Body Mass Calculator, then apply Katch–McArdle by hand if that fits. Tape and BMI-style estimates are still estimates. None of these replace a metabolic cart or a clinician, and a high muscle mass is not a reason to ignore the rest of your health history.
Should I eat at my BMR?
Usually no. BMR is the rest floor, not a meal target. A typical day also includes the thermic effect of food and activity, which is why TDEE is the planning number. Eating at BMR for a stretch can mean a large deficit, fatigue, and a drop in training — not a guaranteed fat-loss plan. The Calorie Calculator applies a conventional ±500 kcal shift around TDEE as a planning offset, not a medical prescription. If you have an eating-disorder history, are pregnant, or live with a metabolic condition, do not set an intake from this widget. Bring the number to a qualified clinician or registered dietitian who can look at the whole file.
Does this calculator work for children or pregnancy?
Mifflin–St Jeor was derived from adult samples. This widget will still arithmetic a number if you enter a child's age or a pregnancy weight, but that number is not validated here for growth, pregnancy, or clinical malnutrition. Children's energy needs are not “tiny adult BMR.” Pregnancy and lactation add cost this formula does not model. The limitations box on this page says the same. Use pediatric or prenatal guidance, not this adult rest estimate, and talk with a clinician who knows the full picture. The NIH materials on weight management are written for adults in the same spirit: a starting input, not a care plan for a growing or pregnant body.
References
- Mifflin et al. — A new predictive equation for resting energy expenditure (1990)
- Harris & Benedict — A biometric study of human basal metabolism (1918)
- Frankenfield et al. — Predictive equations for resting metabolic rate (J Am Diet Assoc, 2005)
- NIH NIDDK — Body Weight Planner
- https://en.wikipedia.org/wiki/Basal_metabolic_rate
Assumptions and limitations
These fitness results are not a medical diagnosis or treatment plan. They use the named screening formulas only and cannot replace advice from a qualified clinician.
Mifflin–St Jeor was derived from adult samples; it is not validated here for children, pregnancy, or clinical malnutrition. The widget does not measure RMR, TDEE, or body composition.