Updated September 2026 Basal Metabolic Rate — calories burned at complete rest. Results shown for both Mifflin-St Jeor and Harris-Benedict formulas.
What is BMR?
Your Basal Metabolic Rate (BMR) is the number of calories your body needs to sustain basic life functions at complete rest — breathing, circulation, temperature regulation, and cell production. Think of it as the energy cost of simply being alive.
BMR typically accounts for 60–75% of total daily calorie expenditure. The remainder comes from physical activity and digesting food. Muscle mass is the largest driver of BMR — the more lean muscle you have, the higher your resting metabolism.
We show two formulas: Mifflin-St Jeor (1990) is considered more accurate for modern populations; Harris-Benedict (revised 1984) has been used longer and may be more familiar to clinicians.
What your BMR actually pays for
Basal metabolic rate is the energy your body spends doing nothing at all — measured, strictly, after an overnight fast, at complete rest, in a thermally neutral room, having not exercised for 24 hours. It is the cost of simply remaining alive, and for most people it is 60 to 70 percent of everything they burn in a day.
| Organ or tissue | Share of resting expenditure | Note |
|---|---|---|
| Liver | ~27% | The single largest consumer, regardless of body size |
| Brain | ~19% | Roughly constant; it does not burn more when you think hard |
| Skeletal muscle | ~18% | At rest. Rises dramatically the moment you move |
| Kidneys | ~10% | Continuous filtration |
| Heart | ~7% | Never stops |
| Everything else | ~19% | Fat tissue included, at roughly 4.5 kcal/kg/day |
That table settles a persistent myth. A kilogram of muscle burns roughly 13 calories a day at rest, against about 4.5 for a kilogram of fat — a real difference, but nothing like the “50 calories per pound” often claimed. Gaining 5 kg of muscle adds perhaps 45 calories a day to your resting rate. Muscle is worth building for strength, health, appearance and the calories it burns while being trained, not for a resting metabolic bonus.
The two equations on this page
We show both because their disagreement is informative.
Men: (10 × kg) + (6.25 × cm) − (5 × age) + 5
Women: (10 × kg) + (6.25 × cm) − (5 × age) − 161
Men: 88.362 + (13.397 × kg) + (4.799 × cm) − (5.677 × age)
Women: 447.593 + (9.247 × kg) + (3.098 × cm) − (4.330 × age)
Harris-Benedict is the older equation — first published in 1919, revised in 1984 — and reliably returns a slightly higher figure, typically 50 to 80 calories above Mifflin-St Jeor. Its original data came from a population whose body composition differed from today’s, which is the usual explanation for the drift. Mifflin-St Jeor is the better default, and the one our TDEE calculator uses.
BMR versus RMR
You will see both terms, often interchangeably. Strictly, basal metabolic rate requires laboratory conditions — overnight fast, full rest, thermoneutral environment. Resting metabolic rate is measured under looser conditions and runs roughly 5 to 10 percent higher. Every predictive equation in common use, including both above, is really predicting RMR. The distinction matters in a metabolic ward and almost nowhere else.
What genuinely changes your BMR
- Body size — the dominant factor by a wide margin. More tissue costs more to maintain, which is why weight loss lowers BMR as a matter of arithmetic.
- Lean mass — the reason two people at the same weight can differ by 100 calories or more, and the reason lean-mass-based equations exist.
- Age — roughly 1 to 2 percent per decade after 20, mostly through muscle loss rather than an intrinsic metabolic decline.
- Thyroid function — genuine and clinically significant. This is the one item on the list worth seeing a doctor about if you suspect it.
- Prolonged dieting — an adaptive reduction of roughly 50 to 100 calories a day beyond what your smaller size predicts. Real, modest, and reversible.
What does not meaningfully change it: green tea, spicy food, meal frequency, drinking cold water, and eating breakfast. Each has been measured, and each is worth single-digit calories.
Using your BMR
BMR on its own is not a calorie target — eating at your BMR would mean a deficit of several hundred calories for anyone who moves at all. Its practical uses are three: as the input to a TDEE calculation, as a floor you should not diet below, and as a baseline to watch over years. If your BMR seems implausibly low or high, the formula comparison page runs six published equations on the same person and shows how much they disagree.
BMR calculator — FAQ
Yes — the most effective way to raise BMR is to build lean muscle mass through resistance training. Muscle tissue burns more calories at rest than fat tissue. Eating adequate protein (0.8–1g per lb of bodyweight), staying hydrated, getting sufficient sleep, and avoiding prolonged severe caloric restriction all help maintain a healthy metabolic rate.
Yes, BMR tends to decline with age — primarily because most people lose muscle mass as they age (a process called sarcopenia). The decline is roughly 1–2% per decade after age 30. However, maintaining muscle through strength training can significantly offset this decline. Age-related metabolic slowdown is largely a loss of muscle story, not an inevitable fate.
They use slightly different coefficients derived from different study populations. The Harris-Benedict equation was developed in 1919 (revised in 1984) and tends to overestimate BMR by 5% on average. The Mifflin-St Jeor equation was published in 1990 using a larger, more diverse population and is now recommended by most dietetic associations as the more accurate formula.
No. Your BMR is what you would burn lying perfectly still all day, so eating at it while living a normal life creates a substantial deficit. Use your TDEE — BMR multiplied by an activity factor — as the basis for any calorie target.
Mifflin-St Jeor. A 2005 review found it the most reliable of the predictive equations for both obese and non-obese adults. Harris-Benedict typically returns 50 to 80 calories more, which is why we show both — the gap is a useful reminder that these are estimates.
Less than commonly claimed. Skeletal muscle burns roughly 13 kcal per kilogram per day at rest, against about 4.5 for fat. Gaining 5 kg of muscle adds perhaps 45 calories a day — worth having, but not a metabolic transformation.
Almost certainly not. Adaptive thermogenesis reduces expenditure by roughly 50 to 100 calories a day beyond what your smaller body size predicts, and it largely reverses when energy availability is restored.