BMR Calculator
Estimate your basal metabolic rate with three published equations at once: Mifflin–St Jeor as the default, the revised Harris–Benedict for comparison, and the lean-mass equation commonly called Katch–McArdle if you know your body fat percentage — with the spread between them shown on screen.
Your details
Your basal metabolic rate is the energy your body spends keeping you alive at complete rest: breathing, circulating blood, maintaining body temperature, running your organs. Measured properly, it requires an overnight fast, a night of rest, and a thermoneutral room — conditions almost nobody meets outside a laboratory. What any online calculator gives you is therefore a prediction of resting energy expenditure from your stats, and the honest framing is "equation-based estimate", not "metabolic test".
This page runs three published equations side by side instead of hiding one behind a settings menu. The default is Mifflin–St Jeor, published in 1990 (Mifflin MD, St Jeor ST, et al. Am J Clin Nutr. 1990;51(2):241-247) and supported as a sensible default for healthy adults by a systematic review of predictive equations (Frankenfield D, et al. J Am Diet Assoc. 2005;105(5):775-789). The revised Harris–Benedict equation from 1984 is shown for compatibility and comparison. The lean-mass equation — commonly called Katch–McArdle, with the same form published by Cunningham in 1991 — appears whenever you provide a body fat estimate, so you can see how much your answer depends on which equation you trust.
The spread between the three is itself the most educational output on this page. For a typical adult it is often a few hundred kilocalories per day; for people with unusual body composition it can be much larger. Rather than silently picking one number, we show the spread, label each equation with its source, and let the comparison do the honesty work.
Mifflin–St Jeor: men 10W + 6.25H − 5A + 5; women 10W + 6.25H − 5A − 161, displayed rounded to 1 kcal.
Revised Harris–Benedict (Roza & Shizgal 1984): men 88.362 + 13.397W + 4.799H − 5.677A; women 447.593 + 9.247W + 3.098H − 4.330A.
Lean-mass equation (commonly called Katch–McArdle; same form in Cunningham 1991): 370 + 21.6 × FFM, where FFM = W × (1 − BF%). Returns null without a body fat input — we guide you to the body fat tool instead of guessing. The panel shows the min, max, and percentage spread across all computed equations.
Conversions use 1 kcal = 4.1868 kJ. Inputs are validated (age, weight, height ranges); body fat accepts 2–60%. All arithmetic runs locally in your browser.
Which BMR equation does this calculator use by default?
The default is Mifflin–St Jeor: for men, 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5; for women, the same expression ends in −161 (Mifflin MD, St Jeor ST, et al. Am J Clin Nutr. 1990;51(2):241-247. DOI:10.1093/ajcn/51.2.241). We default to it because, when a systematic review compared published resting-equations against measured values in healthy non-obese and obese adults, Mifflin–St Jeor was among the equations most often staying within 10% of the measured value (Frankenfield D, et al. J Am Diet Assoc. 2005;105(5):775-789. DOI:10.1016/j.jada.2005.02.005).
Two careful readings of that sentence, because it is easy to over-read. First, "most often within 10%" is a statement about populations of study subjects, not a promise that your individual estimate is within 10% — individual errors exist and can be substantial. Second, it covers healthy adults; it is not a claim about athletes, older adults, or clinical populations, for whom no equation has been crowned a universal winner. That scope is why this page shows alternatives rather than claiming a champion.
Compare all three equations side by side
Every result panel on this page shows the equations together, because the comparison teaches more than any single number:
- Mifflin–St Jeor (1990) — uses weight, height, age, and sex only. Default. Best-documented for general healthy adults.
- Revised Harris–Benedict (Roza & Shizgal 1984) — men: 88.362 + 13.397W + 4.799H − 5.677A; women: 447.593 + 9.247W + 3.098H − 4.330A. The older standard, still common in legacy systems. Note this is the revised 1984 version; the original 1919 equation differs and some sites still run it unlabelled.
- Lean-mass equation, commonly called Katch–McArdle (same form in Cunningham 1991) — 370 + 21.6 × fat-free mass (kg), where fat-free mass = weight × (1 − body fat %). Requires a body fat estimate, so it unlocks only when you provide one; we never switch to it silently. Cunningham's related 1980 version uses a different form (500 + 22 × FFM), so we always cite the year with the equation.
Worked example at 80 kg, 180 cm, 30-year-old male: Mifflin gives about 1,780 kcal/day, revised Harris–Benedict about 1,848, and — at 20% body fat, hence 64 kg of fat-free mass — the lean-mass equation about 1,752. That 100 kcal/day spread across otherwise-identical inputs is the point: your resting estimate carries real model uncertainty, and any plan should absorb it. For a deeper walk through the differences, see TDEE formulas compared.
BMR vs RMR: a terminology note
You will see both terms used interchangeably across the web, including on this page's title, and a short note on what the difference actually is keeps everyone honest. BMR (basal metabolic rate) is measured under the strictest conditions: an overnight fast, at least eight hours of sleep, full physical and mental rest, and a thermoneutral environment. RMR (resting metabolic rate, or resting energy expenditure) is measured under looser "just resting" conditions and is typically a few percent higher, because even quiet sitting and recent meals add a little burn.
The equations here — Mifflin, Harris–Benedict, and the lean-mass form — were validated as predictions of resting energy expenditure, not strict basal rate. Consumer sites, this one included, label their tools "BMR calculators" because that is what people search for, but the number you get is best read as "resting burn, measured loosely". For every practical purpose — feeding a TDEE estimate or setting a calorie target — the distinction does not change what you do with the number.
Sanity-check band for your result
The result panel flags estimates that fall outside the pattern these equations were validated on. For a typical adult, resting estimates below about 1,000 kcal/day or above about 2,500 kcal/day are unusual, and inputs outside the validated ranges (age 10–100, weight 30–250 kg, height 120–220 cm — we accept only adult inputs here) are blocked at the form. A flagged result almost always means an input error; if the inputs are genuinely correct, a population equation may simply be a poor fit for you.
The systematic review behind our default choice also notes that older adults were under-represented in the underlying validation studies, and athlete studies show high variability between equations — group averages landing near measured values does not mean any individual estimate is reliable. If your result matters for a medical or performance decision and looks inconsistent with your experience, the only definitive answer is a measured resting metabolic rate from a professional; no equation on this page can substitute for that.
Frequently asked questions
What is the difference between BMR and RMR?
BMR is measured under the strictest conditions — overnight fast, full rest, thermoneutral room — while RMR is measured under ordinary quiet resting conditions and is typically a few percent higher. The published equations on this page predict resting energy expenditure (the looser quantity), even though the tool is labelled "BMR calculator" because that is the term people search for. In practice the distinction rarely changes what you do with the number.
Which BMR equation is most accurate?
For generally healthy adults, Mifflin–St Jeor is the best-documented default: a systematic review found it among the equations most often within 10% of measured resting expenditure. But that is population-level evidence, not an individual guarantee, and no equation is a universal winner across athletes, older adults, and clinical populations. That is why this page shows the revised Harris–Benedict and the lean-mass equation next to it — the spread between them is a visible measure of your uncertainty.
Why does the Katch–McArdle number differ from Mifflin?
Because it uses different information. The equation commonly called Katch–McArdle (same form published by Cunningham in 1991) is built on fat-free mass — 370 + 21.6 × FFM — instead of weight, height, and age. Two people with identical stats but different body composition get the same Mifflin result and different lean-mass results. It requires a trustworthy body fat estimate; a cheap bathroom-scale reading can be off by several percentage points, which can move the result by more than the equation switch itself.
Can I raise my BMR?
Modestly, and mostly indirectly. Building muscle adds a small amount of resting expenditure (muscle is more metabolically active than fat, though less than pop articles suggest); gaining significant weight raises it too. Large sustained increases from a single food, supplement, or cold exposure habit are not supported by evidence worth planning around. Note also that prolonged dieting pushes resting expenditure down — metabolic adaptation — which is the flip side people notice more.
Why is my BMR lower than my friend's even though I exercise more?
Resting burn scales primarily with body size and composition: a heavier or taller person usually has a higher resting estimate than a lighter or shorter one, regardless of fitness. Training raises total daily burn (through activity) far more than it raises resting burn. Sex and age also shift the constants. Comparing raw BMR numbers across different bodies is mostly comparing body sizes.
Does dieting permanently damage my metabolism?
Prolonged energy restriction lowers resting expenditure beyond what weight loss alone predicts — the adaptive component documented in dynamic weight models (Hall KD, et al. Lancet. 2011). For most people it partially rebounds after the deficit ends and weight stabilises; "permanent damage" is not what the evidence shows for typical dieting. The practical takeaway for this page: after a long cut, recalculate rather than reusing your old number, and treat any resting estimate as a snapshot, not a constant.
References & sources
Mifflin MD, St Jeor ST, et al. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 1990;51(2):241-247. DOI:10.1093/ajcn/51.2.241.
Supports: The default resting-energy-expenditure equation and its constants.
Does not support: Does not address activity multipliers, macronutrients, or weight-change timelines built on the estimate.
Frankenfield D, Roth-Yousey L, Compher C. Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review. J Am Diet Assoc. 2005;105(5):775-789. DOI:10.1016/j.jada.2005.02.005.
Supports: The basis for defaulting to Mifflin–St Jeor among published equations for healthy adults, and the note that older adults were under-represented.
Does not support: Does not establish an individual error guarantee, nor a winner for athletes or clinical populations.
Roza AM, Shizgal HM. The Harris Benedict equation reevaluated: resting energy requirements and the body cell mass. Am J Clin Nutr. 1984;40(1):168-182. DOI:10.1093/ajcn/40.1.168.
Supports: The revised Harris–Benedict equation shown for side-by-side comparison.
Does not support: Not the 1919 original; validation findings for the original should not be assumed to carry over to this revision.
Cunningham JJ. Body composition as a determinant of energy expenditure: a synthetic review and a proposed general prediction equation. Am J Clin Nutr. 1991;54(6):963-969. DOI:10.1093/ajcn/54.6.963.
Supports: The lean-mass equation (370 + 21.6 × FFM) commonly called Katch–McArdle; Cunningham's distinct 1980 version is 500 + 22 × FFM.
Does not support: Does not mean knowing body fat always beats Mifflin — athlete studies are heterogeneous, and the result is only as good as the body fat input.