Calculate your Basal Metabolic Rate using the Mifflin-St Jeor equation — see your minimum daily calorie floor and compare all major BMR formulas including Harris-Benedict and Katch-McArdle.
This BMR Calculator applies the Mifflin-St Jeor equation — the current standard recommended by the American Dietetic Association — to estimate the calories your body burns at complete rest over 24 hours. It accepts height, weight, age, and sex, and it returns your BMR in kcal/day. BMR is specifically the rate at which energy is expended under post-absorptive conditions (having not eaten for 12 hours) in a thermoneutral environment — meaning it strips out all activity and digestion. In practical terms, it represents the lowest daily calorie floor: eating fewer calories than your BMR for an extended period would put your body under physiological stress. Understanding your BMR is the first step toward calculating your TDEE (total daily energy expenditure), which adjusts BMR upward for activity. This is an educational estimate — a registered dietitian can provide a more individualized assessment.
The basal metabolic rate (BMR) is the amount of energy needed while resting in a temperate environment when the digestive system is inactive. It is the equivalent of figuring out how much gas an idle car consumes while parked. In such a state, energy will be used only to maintain vital organs, which include the heart, brain, kidneys, nervous system, intestines, liver, lungs, sex organs, muscles, and skin.
For most people, upwards of ~70% of total energy (calories) burned each day is due to upkeep. Physical activity makes up ~20% of expenditure and ~10% is used for the digestion of food, also known as thermogenesis.
The BMR is measured under very restrictive circumstances while awake. An accurate BMR measurement requires that a person's sympathetic nervous system is inactive, which means the person must be completely rested. Basal metabolism is usually the largest component of a person's total caloric needs. The daily caloric need is the BMR value multiplied by a factor with a value between 1.2 and 1.9, depending on activity level.
Enter your sex, age, height, and current weight in your preferred units and tap calculate. The result is your estimated BMR in calories per day. A typical American woman might see a BMR between 1,300 and 1,600 kcal/day; a typical American man between 1,600 and 2,000 kcal/day, though values vary significantly with body size and age. Your BMR is not your daily calorie target — it's the foundation. To find how many calories you actually need, multiply BMR by your activity multiplier in the TDEE Calculator. If your goal is weight loss, your daily intake should typically fall somewhere between your BMR and your TDEE — never below BMR without medical supervision.
The Mifflin-St Jeor equation:
Men:
BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) + 5
Women:
BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) − 161
Example — 35-year-old woman, 5'5" (165 cm), 140 lb (63.5 kg):
BMR = (10 × 63.5) + (6.25 × 165) − (5 × 35) − 161 = 635 + 1031.25 − 175 − 161 = 1,330 kcal/day
Example — 35-year-old man, 5'10" (178 cm), 180 lb (81.6 kg):
BMR = (10 × 81.6) + (6.25 × 178) − (5 × 35) + 5 = 816 + 1112.5 − 175 + 5 = 1,758.5 kcal/day
The Mifflin-St Jeor Equation is considered the most accurate for calculating BMR, except that the Katch-McArdle Formula can be more accurate for leaner individuals who know their body fat percentage.
No — and confusing them is one of the most common calorie calculation mistakes. BMR is what you burn doing absolutely nothing: no movement, no digestion, just staying alive. TDEE (Total Daily Energy Expenditure) is BMR multiplied by an activity factor that accounts for everything you actually do each day. A sedentary person multiplies BMR by 1.2; a lightly active person by 1.375; moderate activity by 1.55; active by 1.725; very active by 1.9. The gap between BMR and TDEE for a typical moderately active adult is substantial — often 500–800 kcal/day. Setting a calorie goal at your BMR level and calling it your "maintenance" is a common error that creates an accidental deficit large enough to trigger metabolic adaptation. Use the TDEE Calculator to complete the picture.
BMR isn't fixed. It declines with age — roughly 1–2% per decade after 30 — primarily because muscle mass decreases and fat mass tends to increase, and muscle tissue is metabolically more active than fat. A 50-year-old has a measurably lower BMR than their 25-year-old self even at the same body weight. The NIH notes that this metabolic slowdown is one reason weight management becomes more challenging with age. The practical implication: resistance training, which builds and preserves lean mass, is one of the most effective tools for slowing BMR decline. Every pound of muscle burns approximately 6 kcal/day at rest — modest in isolation but meaningful across an entire body. Sedentary aging accelerates the BMR drop; active aging blunts it.
Anaerobic exercises like weight-lifting build muscle mass, increasing resting energy consumption. More muscle means higher BMR.
The more elderly and limber an individual, the lower their BMR, requiring less caloric intake to sustain organ function.
Hereditary traits passed down from ancestors influence your basal metabolic rate.
Cold environments raise BMR due to energy required for body temperature. BMR increases ~7% for every 1.36°F rise in internal body temperature.
Small, routinely dispersed meals increase BMR. Starvation can reduce BMR by up to 30%.
Ensuring the livelihood of a fetus increases BMR. Menopause can increase or decrease BMR depending on hormonal changes.
Certain supplements like caffeine raise BMR, mostly to fuel weight loss.
If BMR represents your floor, any weight-loss plan should stay above it — or at minimum, should only briefly dip toward it under medical supervision. The NIDDK Body Weight Planner shows that a sustainable calorie deficit of 500–1,000 kcal/day below TDEE (not BMR) produces the evidence-based 1–2 lbs/week of loss recommended by the CDC. Eating at or below BMR for extended periods triggers metabolic adaptation — the body downregulates energy expenditure — which is the underlying mechanism behind the "plateau" many dieters hit. It can also accelerate lean mass loss, lower thyroid output, and suppress non-exercise activity thermogenesis (NEAT). The practical rule: set your calorie target below TDEE, above BMR, and prioritize the gap being created by activity as much as by food reduction.
The Harris-Benedict equation (1919, revised 1984) was the original gold standard. The Mifflin-St Jeor equation (1990) was developed on a more modern, larger population and has since been validated in multiple studies. A widely cited 2005 comparison published in the Journal of the American Dietetic Association (Frankenfield et al.) found Mifflin-St Jeor accurate within 10% for about 82% of non-obese subjects, outperforming Harris-Benedict. For people with obesity, Mifflin-St Jeor still performs better, though the Mifflin equation was originally developed without a large obese sample, so error margins are somewhat wider at higher body weights. A third option — the Katch-McArdle equation — uses lean body mass rather than total weight and can be more accurate for athletes and lean individuals, but it requires a body fat measurement as an input.
Online BMR tests with rigid formulas are not the most accurate method. It's better to consult a certified specialist or measure BMR through a calorimetry device. These handheld devices are available in many health and fitness clubs, doctor offices, and weight-loss clinics.
Resting metabolic rate (RMR) is the rate at which the body burns energy in a relaxed, but not fully inactive state. BMR requires total physiological equilibrium while RMR conditions can be altered and defined by contextual limitations.
A 2005 meta-analysis study on BMR showed that when controlling all factors of metabolic rate, there is still a 26% unknown variance between people. Essentially, an average person eating an average diet will likely have expected BMR values, but there are factors still not understood that determine BMR precisely.
Therefore, all BMR calculations, even using the most precise methods through specialists, will not be perfectly accurate. A calculated BMR may result in unsatisfactory results, but maintaining a daily journal of exercise, food consumption, etc., can help track factors that lead to results and help determine what works for you.
Reference: Johnstone AM, Murison SD, Duncan JS, Rance KA, Speakman JR. Factors influencing variation in basal metabolic rate include fat-free mass, fat mass, age, and circulating thyroxine but not sex, circulating leptin, or triiodothyronine. Am J Clin Nutr 2005; 82: 941-948.
The Mifflin-St Jeor formula weighs four variables: sex (men have higher BMR by ~166 kcal/day built into the formula constant), weight (the single biggest lever — heavier bodies burn more at rest), height (taller people have more tissue), and age (BMR declines roughly 10 kcal/day per decade). Body composition is the factor the formula doesn't directly capture: two people with the same weight and height can have different BMRs if one is more muscular. Thyroid function significantly affects actual resting metabolism — hypothyroidism can lower BMR by 20–40% — but no formula accounts for this without a lab test. Fever raises BMR approximately 7% per degree Fahrenheit. Pregnancy increases BMR progressively across trimesters.
Lisa is a marketing director, 5'6" (168 cm) and 155 lb (70.3 kg). BMR = (10 × 70.3) + (6.25 × 168) − (5 × 42) − 161 = 703 + 1050 − 210 − 161 = 1,382 kcal/day. Lisa works at a desk and does light yoga twice a week. Her TDEE (BMR × 1.375) ≈ 1,900 kcal/day. A 500 kcal/day deficit puts her at 1,400 kcal — barely above her BMR. She'd be better served by increasing activity to raise her TDEE, giving her more room to eat while still losing weight.
James is a firefighter, 6'1" (185 cm) and 210 lb (95.3 kg). BMR = (10 × 95.3) + (6.25 × 185) − (5 × 27) + 5 = 953 + 1156.25 − 135 + 5 = 1,979 kcal/day. James is physically active most days (multiplier 1.725), giving him a TDEE of about 3,413 kcal. His BMR is only 58% of his total burn — the rest is the energy cost of his active lifestyle. A 500 kcal deficit for him means 2,913 kcal/day, which feels satisfying rather than restrictive.
Use your BMR as a floor, not a target — never build a long-term weight plan that puts daily intake at or below this number.
Recalculate BMR every 10–15 lbs of weight change, because the formula's weight input changes meaningfully at that scale.
If your weight has been stable for years despite eating at what seems like your TDEE, suspect that your actual BMR differs from the formula — consider an indirect calorimetry test at a sports medicine clinic for a precise measurement.
Prioritize muscle-building resistance training to slow age-related BMR decline — it's the only behavioral lever that raises the number.
Be honest about your activity level when moving from BMR to TDEE — most people overestimate activity, which is why TDEE-based calorie plans often produce less loss than expected.
For thyroid conditions or hormonal imbalances, consult a healthcare provider before relying on formula-based BMR estimates.
For most adult women in the US, BMR calculated by the Mifflin-St Jeor equation typically falls between 1,200 and 1,600 kcal/day, depending on age, height, and weight. Smaller, older women tend toward the lower end.
For adult men, Mifflin-St Jeor BMR commonly falls between 1,500 and 2,100 kcal/day. Larger, younger, and more muscular men have higher BMRs.
No. BMR is your at-rest calorie burn; TDEE multiplies BMR by an activity factor (1.2–1.9) to estimate total daily burn including all movement and exercise. Use the TDEE Calculator to get your full daily number.
The most effective approach is building lean muscle mass through resistance training — more muscle means higher resting energy expenditure. Adequate sleep, staying hydrated, and avoiding prolonged very-low-calorie dieting also help preserve BMR.
Yes. BMR declines approximately 1–2% per decade after age 30, mainly due to loss of lean muscle mass. Staying active and maintaining muscle mass significantly slows this decline.
No. Your daily intake for weight loss should sit between your BMR and your TDEE — a 500–1,000 kcal deficit from TDEE is the standard guideline. Eating at or below BMR risks metabolic slowdown, muscle loss, and nutritional deficiency.
It's the most commonly recommended BMR formula: Men: 10×kg + 6.25×cm − 5×age + 5; Women: 10×kg + 6.25×cm − 5×age − 161. A 2005 study found it more accurate than Harris-Benedict for most adults.
Brief disclaimer: This calculator provides educational estimates using the Mifflin-St Jeor equation. BMR calculations carry inherent variance — research shows approximately 26% unexplained variance between individuals even after controlling for all known factors. Results should be treated as a starting point for understanding your energy needs, not as clinical measurements. Consult a registered dietitian or healthcare provider for personalized metabolic assessment and dietary planning.