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BMR Calculator
Your BMR — basal metabolic rate — is the energy your body spends at complete rest: heart beating, lungs breathing, brain thinking, cells repairing. This BMR calculator estimates it with three published equations and shows you the formula, not just the answer.
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BMR is the foundation of all calorie math. It typically accounts for 60–70% of everything you burn in a day, which is why two people with the same workout routine can have wildly different calorie needs: the engine idling underneath differs. Muscle mass, height, age, and sex drive most of that difference.
One clarification worth making early: you never eat at your BMR. It's a component, not a target. Your actual daily needs are your BMR multiplied by an activity factor — that's your TDEE, and it's what our TDEE calculator and calorie calculator are for.
The three BMR equations, compared
Mifflin-St Jeor (1990) is our default and the one to use unless you have a reason not to: in the Academy of Nutrition and Dietetics' comparison it predicted measured resting metabolic rate within 10% for more adults than any competing equation. It needs only sex, age, height, and weight.
The revised Harris-Benedict equation (1984) is the classic — it defined this field for seventy years and still appears in textbooks and hospital charts. It tends to estimate slightly higher than Mifflin-St Jeor, particularly for heavier people, which is exactly why it was eventually superseded.
Katch-McArdle takes a different route: it ignores age and sex entirely and computes from lean body mass (370 + 21.6 × lean kg). If you have a reliable body-fat measurement, it's the best choice for very muscular or very lean physiques, where weight-based formulas drift.
What a 'normal' BMR looks like
For most adult women, BMR falls between 1,200 and 1,600 kcal per day; for most adult men, between 1,500 and 2,000. Bigger and younger bodies sit higher; smaller and older bodies sit lower. BMR declines roughly 1–2% per decade after your twenties, mostly because muscle mass declines — which is also the lever you control.
Strength training is the most reliable way to nudge BMR upward, because muscle is metabolically expensive tissue while fat is cheap to maintain. Crash dieting is the fastest way to push it down: severe restriction triggers adaptive thermogenesis, where your body deliberately economizes. This is why sustainable deficits beat aggressive ones on every timescale beyond a month.
BMR vs. RMR — and why the difference rarely matters
Technically, BMR is measured under strict lab conditions — overnight fast, complete rest, temperature-controlled room, just after waking — while RMR (resting metabolic rate) is measured under looser, more realistic conditions and runs a few percent higher. Prediction equations like Mifflin-St Jeor were actually validated against RMR.
In practice the two terms are used interchangeably, and for planning your nutrition the distinction is noise: the activity multiplier you apply next carries far more uncertainty than the BMR/RMR gap. Know the difference exists, then move on to the number that matters — your TDEE.
Frequently asked questions
BMR (basal metabolic rate) is the number of calories your body burns at complete rest just to stay alive — powering your heart, lungs, brain, liver, and cell repair. It typically represents 60–70% of your total daily calorie burn.
For most healthy adults, Mifflin-St Jeor — the Academy of Nutrition and Dietetics found it most often predicts measured values within 10%. If you know your body-fat percentage accurately, Katch-McArdle can be better for very muscular or very lean bodies because it works from lean mass.
No. BMR is what you burn at total rest; you burn more than that even on a lazy day. Eating at BMR usually creates an unnecessarily aggressive deficit. Instead, calculate your TDEE (BMR × activity) and subtract 250–500 kcal from that.
Meaningfully, yes — by building muscle through strength training, which raises your resting burn. Protein also has a higher digestion cost than carbs or fat. What lowers BMR: aging, losing muscle, and prolonged severe calorie restriction.