Results update live as you type after first calculation.
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Enter your details and tap Calculate BMR to see your personalised basal metabolic rate, TDEE across all activity levels, and a full formula comparison.
Basal Metabolic Rate
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kcal / day
Mifflin-St Jeor
Lean Body Mass
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kg
% of Daily Calories
~60–75%
at sedentary activity
kcal / hour
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at rest
Daily Calorie Breakdown
Basal Metabolic Rate
-- kcal
~70% · organ function at rest
Physical Activity (NEAT)
-- kcal
~20% · movement & exercise
Thermic Effect of Food
-- kcal
~10% · digesting food
Formula Comparison
Mifflin-St Jeor
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kcal/day
Recommended
Harris-Benedict
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kcal/day
Katch-McArdle
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kcal/day · needs BF%
The active formula is highlighted in green. Katch-McArdle uses your entered body fat % (default 20%). Use our Calorie Calculator to apply your BMR with a specific goal.
Daily Calorie Needs by Activity Level
Activity Level
×
kcal / day
TDEE by Activity Level — Chart
Total daily calorie needs across all six activity levels, based on your BMR.
BMR is an estimate. Actual metabolic rate varies by genetics, hormones, and health status. A 2005 meta-analysis found a ±26% variance in BMR between individuals even when controlling for known factors. For precise measurement, consult a specialist using indirect calorimetry.
Understanding Your Basal Metabolic Rate
Your basal metabolic rate (BMR) is the number of calories your body burns every day just to stay alive — no movement, no digestion, no exercise. It is the energy cost of keeping your heart beating, your lungs breathing, your kidneys filtering, and every cell in your body functioning at rest. Understanding your BMR is the foundation of any nutrition or weight management plan, because it sets the absolute minimum calorie floor below which your body will begin to cannibalise its own tissue. Our free online metabolic rate calculator uses the three most clinically validated basal metabolic rate formulas — Mifflin-St Jeor, Harris-Benedict, and Katch-McArdle — so you can see your results side by side and understand which estimate best fits your body.
What Is Basal Metabolic Rate?
The basal metabolic rate is measured under strict conditions: the person must be fully rested (lying still, but awake), in a thermally neutral environment (around 22°C / 72°F), and in a post-absorptive state — meaning at least 12 hours after the last meal, so the digestive system is completely inactive.
For most adults, BMR accounts for 60–75% of total daily calorie expenditure. The remaining ~20% comes from physical activity and movement (NEAT — Non-Exercise Activity Thermogenesis), and ~10% from the thermic effect of food (the energy spent digesting, absorbing, and metabolising nutrients).
BMR is often confused with Resting Metabolic Rate (RMR). They are similar but not identical: BMR requires stricter measurement conditions, while RMR is measured under more relaxed conditions and is typically 10–20% higher. Most basal caloric rate calculators — including this one — technically estimate RMR, because true BMR measurement requires a clinical metabolic lab.
The Basal Metabolic Rate Formula
Three main basal metabolic rate formulas are used in clinical and fitness practice. Each was developed using different research populations and methodologies, which is why they produce slightly different results:
W = weight (kg) · H = height (cm) · A = age (years). Endorsed by the Academy of Nutrition and Dietetics as the most accurate general-population formula.
Originally published 1919, revised by Roza & Shizgal in 1984. Still widely used; slightly overestimates BMR compared to Mifflin in modern populations.
Katch-McArdle — Best for Lean Individuals
BMR = 370 + 21.6 × Lean Mass (kg)
Lean Mass = Weight × (1 − Body Fat%). Only formula that accounts for body composition. Most accurate for athletes and lean individuals who know their body fat percentage.
From BMR to TDEE — Activity Multipliers
Your Total Daily Energy Expenditure (TDEE) is your BMR multiplied by an activity factor. This is the number of calories you need to consume each day to maintain your current weight — and the starting point for any weight-loss or muscle-gain calculation.
Sedentary (×1.2): Desk job, no planned exercise. BMR covers most needs.
Light (×1.375): 1–3 days/week of light exercise such as walking or yoga.
Moderate (×1.55): 4–5 days/week of gym training or jogging.
Active (×1.725): Hard daily exercise — running, CrossFit, team sports.
Very Active (×1.9): Intense exercise 6–7 days/week; competitive athletes.
Extra Active (×2.1): Twice-daily training plus a physically demanding job.
The TDEE table in the results above shows your exact calorie need at every level simultaneously, so you can plan for any scenario without recalculating. Use our Calorie Intake Calculator to apply a specific deficit or surplus toward your goal.
What Factors Affect Your BMR?
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Muscle Mass
Muscle tissue burns roughly 3× more calories at rest than fat tissue. Every kg of lean muscle added to your body raises BMR by approximately 13 kcal/day. Resistance training is the most reliable way to raise your basal caloric rate long-term.
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Age
BMR decreases by roughly 1–2% per decade after age 20, primarily due to age-related muscle loss (sarcopenia). A 60-year-old typically has a BMR 10–15% lower than they did at 30, even at the same body weight.
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Genetics & Hormones
Thyroid hormones directly regulate metabolic rate — hyperthyroidism raises BMR, hypothyroidism lowers it. A 2005 meta-analysis found a ±26% unexplained BMR variance between individuals even after controlling for all known variables.
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Temperature
Cold environments raise BMR as your body generates heat to maintain core temperature. BMR increases ~7% for every 1.36°F (0.76°C) rise in internal body temperature — which is why fever significantly raises calorie burn.
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Diet History
Severe calorie restriction can suppress BMR by up to 30% through metabolic adaptation — a survival mechanism sometimes called "starvation mode." Small, consistent meals throughout the day have been shown to maintain a higher metabolic rate than large, infrequent ones.
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Pregnancy
Pregnancy raises BMR progressively through all three trimesters as the body supports fetal growth. Menopause can also significantly alter metabolic rate due to hormonal changes affecting lean mass and fat distribution.
BMR vs RMR — What's the Difference?
Basal Metabolic Rate (BMR) and Resting Metabolic Rate (RMR) are often used interchangeably, but there is a meaningful clinical distinction:
BMR is measured under total physiological equilibrium: waking, 12-hour fasted, in a thermoneutral environment, in a fully rested state after sleep. It represents the absolute minimum metabolic floor.
RMR is measured at rest but under less strict conditions — the person does not need to be fasted or in a controlled temperature environment. RMR is typically 10–20% higher than BMR.
Most online metabolic rate calculators — including this one — technically estimate RMR, since the Mifflin-St Jeor and Harris-Benedict equations were derived from resting (not strictly basal) conditions.
For practical weight management purposes, the distinction rarely matters — both give you the same actionable starting point.
How to Use Your BMR Result
Never eat below your BMR. Your BMR is the minimum calorie floor for organ function. Chronic intake below BMR causes metabolic adaptation, muscle loss, nutrient deficiencies, and hormonal disruption.
Find your maintenance calories (TDEE). Multiply your BMR by the activity multiplier that best matches your lifestyle. This is your daily intake to stay at your current weight.
Apply a goal-based adjustment. Subtract 500 kcal from TDEE for ~1 lb/week fat loss; add 500 kcal for ~1 lb/week lean gain. Use our Calorie Calculator for a complete goal-based plan.
Recalculate as weight changes. BMR changes as you lose or gain weight. Recalculate every 4–6 weeks to keep your calorie targets accurate and avoid plateaus.
Increase your BMR long-term. Build muscle through resistance training — every additional kg of lean mass raises your BMR by ~13 kcal/day, creating a larger calorie buffer for fat loss.
Frequently Asked Questions
What is basal metabolic rate?
Basal metabolic rate (BMR) is the number of calories your body burns each day at complete rest to maintain essential life functions — breathing, circulation, temperature regulation, cell repair, and organ operation. It represents roughly 60–75% of your total daily calorie expenditure and is the foundation of every nutrition and weight management calculation.
Which basal metabolic rate formula is most accurate?
The Mifflin-St Jeor equation (1990) is considered the most accurate general-population basal metabolic rate formula and is recommended by the Academy of Nutrition and Dietetics. The Katch-McArdle formula can be more accurate for lean or athletic individuals who know their body fat percentage, because it accounts for lean body mass rather than total weight.
How accurate is an online metabolic rate calculator?
An online metabolic rate calculator using the Mifflin-St Jeor formula is accurate within ±10% for most healthy adults. However, a 2005 meta-analysis (Johnstone et al.) found a 26% unexplained variance in BMR between individuals even after controlling for fat mass, fat-free mass, age, and hormones. For the most precise BMR measurement, indirect calorimetry via a handheld metabolic testing device is recommended.
What is the difference between BMR and TDEE?
BMR is your calorie burn at complete rest. TDEE (Total Daily Energy Expenditure) is BMR multiplied by an activity factor that accounts for your daily movement, exercise, and physical work. TDEE is the total calories you need to consume to maintain your current weight. To lose weight, consume less than your TDEE; to gain weight, consume more.
Can I raise my basal metabolic rate?
Yes — the most effective long-term strategy to raise your basal caloric rate is to build muscle through progressive resistance training. Each additional kg of lean muscle raises BMR by approximately 13 kcal/day. Eating adequate protein (0.7–1 g per lb bodyweight) supports muscle retention. Avoiding prolonged severe calorie restriction also prevents the metabolic adaptation that can lower BMR by up to 30%.
What is the difference between BMR and RMR?
BMR requires strict measurement conditions — fully rested, 12-hour fasted, thermoneutral environment. RMR (Resting Metabolic Rate) is measured under less strict conditions and is typically 10–20% higher than true BMR. Most basal metabolic rate calculators online, including this one, technically estimate RMR — but for practical nutrition planning the distinction is minor and both values serve the same purpose.
Medical Disclaimer: The basal metabolic rate and TDEE values calculated by this tool are estimates based on population-level formulas for educational and informational purposes only. Individual metabolic rate varies significantly based on genetics, hormonal status, health conditions, and body composition. These figures are not a substitute for professional medical or nutritional advice. Always consult a qualified healthcare provider or registered dietitian before making significant changes to your diet or exercise plan.
