Answer: Enter your details and the BMR Calculator returns your personalized daily target with the underlying calculation shown step by step.
A BMR calculator estimates your basal metabolic rate — the calories your body burns at complete rest — using the Mifflin-St Jeor or Harris-Benedict equations.
Basal Metabolic Rate — calories burned at rest
Enter age, sex, height, and weight, and the calculator estimates your basal metabolic rate — the energy your body burns at complete rest — using the Mifflin-St Jeor equation, then applies an activity multiplier to estimate total daily energy expenditure (TDEE). The formula, published in 1990 by Mifflin and colleagues, is: for men, BMR = 10×kg + 6.25×cm − 5×age + 5; for women, the same with − 161 in place of + 5. Everything computes locally in your browser.
A 30-year-old man, 75 kg, 175 cm: 750 + 1,094 − 150 + 5 = 1,699 kcal/day. A 30-year-old woman, 63 kg, 165 cm: 630 + 1,031 − 150 − 161 = 1,350 kcal/day. The gap between them is arithmetic, not metabolism: the sex constant alone is worth 166 kcal/day, and each kilogram of body weight adds roughly 10 kcal/day of resting burn.
If you know your body fat percentage, the Katch-McArdle formula offers a cross-check built on lean mass instead: 370 + 21.6 × lean kg. Our example man at 17% body fat carries 62.25 kg of lean mass, giving 370 + 1,345 = 1,715 kcal/day, within about 1% of Mifflin's estimate. When the two formulas disagree badly, trust the lean-mass version, because it's the only one that can see your composition — the body fat calculator supplies that lean-mass number.
| Metric | Men | Women | Units |
|---|---|---|---|
| BMR formula constant (weight term) | × 10 × kg | × 10 × kg | kcal/day base |
| Height coefficient | × 6.25 × cm | × 6.25 × cm | kcal/day per cm |
| Weight coefficient | 10 | 10 | — |
| Age coefficient | − 5 × years | − 5 × years | kcal/day per year |
| Sex constant | + 5 | − 161 | kcal/day |
| Sedentary multiplier (TDEE) | × 1.2 | × 1.2 | applied to BMR |
| Moderate exercise multiplier | × 1.55 | × 1.55 | applied to BMR |
| Very active multiplier | × 1.725 | × 1.725 | applied to BMR |
Reading the coefficients tells you why bodies differ: each additional kilogram adds about 10 kcal/day to BMR, each centimeter of height about 6.25, and each year of age subtracts 5 — while the sex constant alone separates otherwise-identical men and women by 166 kcal/day. Two caveats keep the numbers honest: the equation was developed in generally healthy adults, and it does not know your body composition. Muscular people burn more than it predicts and carry less fat than it assumes; the reverse holds for lower muscle mass.
There's no single normal — size sets the range — but computed reference points help you sanity-check a result:
| Profile (Mifflin-St Jeor) | Age 25 | Age 45 | Age 65 |
|---|---|---|---|
| Woman, 163 cm (5'4"), 63 kg (139 lb) | 1,363 | 1,263 | 1,163 |
| Man, 175 cm (5'9"), 77 kg (170 lb) | 1,744 | 1,644 | 1,544 |
Most adult BMRs land somewhere between roughly 1,100 and 1,900 kcal/day, with bigger and more muscular people above that band. If your result and a friend's differ by several hundred calories, that's body size, not one of you having a broken metabolism. For the full walkthrough, see how to calculate BMR.
BMR is a floor, not a budget. Total daily energy expenditure stacks activity on top: digestion (the thermic effect of food, roughly a tenth of intake), exercise, and non-exercise movement. The standard Harris-Benedict-derived multipliers in the calculator — 1.2 for sedentary, 1.375 for light activity, 1.55 for moderate, 1.725 for very active, 1.9 for extra active — are the conventional way to bridge the gap. Most people overestimate their multiplier; desk workers who train a few times a week usually belong at 1.375-1.55, not 1.725.
Direct measurement puts the equations in perspective: lab indirect calorimetry, the reference method, typically finds standard equations within roughly 10% of measured BMR for most people. That error band is wider than the deficit most diets prescribe, which is why every competent plan starts with an estimate and then adjusts from real-world weekly weight data.
BMR anchors the arithmetic of weight change: eating below TDEE loses weight, above gains — with the widely used rule of thumb that a deficit of about 500 kcal/day corresponds to roughly a pound of fat loss per week (fat stores about 3,500 kcal per pound). The rule is a simplification — metabolism adapts as weight falls — but it sets correct expectations for pace.
Practical cautions: BMR equations are inappropriate during pregnancy, unreliable in illness, and never a substitute for clinical guidance in eating-disorder contexts; minimum safe intake levels exist for a reason. Track weight over two to three weeks against your logged intake and adjust; the scale's trend line is better feedback than any formula's point estimate.
Several BMR equations are still in circulation, and they don't agree — which is why different calculators return different numbers for the same body:
| Formula | Year | Inputs | Notes |
|---|---|---|---|
| Mifflin-St Jeor | 1990 | Sex, weight, height, age | General-population default; within ~10% of lab values for most adults |
| Harris-Benedict (rev. 1984) | 1919/1984 | Sex, weight, height, age | Still powers many websites; runs roughly 5% high |
| Katch-McArdle | — | Lean body mass | Better for lean or muscular people; needs body fat % |
| Cunningham | 1980 | Lean body mass | Similar logic; common in sports-science settings |
Predictive equations carry caveats at the edges of the population. Mifflin-St Jeor was validated in healthy adults, so it loses accuracy in underweight, obesity at higher BMI classes, older age, and clinical conditions that change metabolism (thyroid disease, cancer, burns, critical illness). Athletes with high lean mass are often under-predicted because the equation cannot see body composition; that is precisely the gap Katch-McArdle fills by computing from lean body mass instead of total weight. None of these formulas applies during pregnancy, and pediatric BMR uses entirely different equations. If a clinical decision hinges on energy needs — refeeding, renal disease, post-surgical recovery — the estimate should come from a dietitian, ideally grounded in measured rather than predicted expenditure.
It also helps to know where BMR sits among the competing acronyms. Resting metabolic rate (RMR) is measured under less strict conditions than BMR — lying quietly rather than fasted, post-absorptive, and thermoneutral — so RMR comes out slightly higher in practice, and the two terms are often used interchangeably in popular material even though labs distinguish them. Older equations survive in the wild too: the original Harris-Benedict (1919) and its 1984 revision still appear on many websites, and the World Health Organization tables are common in clinical settings. When you compare calculator outputs across sites and see 100-200 kcal/day differences, the usual explanation is simply that different formulas were applied to the same body — not that one is wrong.
Which equation is most accurate? Mifflin-St Jeor is the current general-population default and outperformed older equations in validation work; Katch-McArdle may fit lean athletes better if body fat percentage is known.
Should I eat at my BMR to lose weight? Deficits are usually taken from TDEE, not BMR — eating at BMR while active already implies a large deficit.
Why does my BMR drop with age? Largely lean-mass loss over time plus the formula's age term; strength training slows both.
Is BMR the same as metabolism? BMR is resting energy use; total metabolism also includes activity and digestion captured by TDEE.
How accurate are the multipliers? Rough by nature — pick conservatively, then adjust from two weeks of real weight and intake data.
Is BMR the same as RMR? Almost — BMR is measured under strict lab conditions (fasted, still, thermoneutral) and RMR under looser ones, so RMR reads slightly higher. In practice the terms get used interchangeably and the formulas estimate the same thing.
Why is my BMR different on different websites? Usually different equations, not different biology. Sites running Harris-Benedict return roughly 5% more than Mifflin-St Jeor — often a 100 kcal/day gap — and Katch-McArdle gives yet another answer if body fat percentage is involved.