BMR Calculator
Calculate your Basal Metabolic Rate (BMR) and daily calorie requirements based on your activity level. Use Mifflin-St Jeor or Harris-Benedict formulas to plan your diet and weight goals.
How to Use
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Select your unit system: Metric (kg, cm) or Imperial (lbs, inches)
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Choose your biological sex
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Select your preferred BMR equation (Mifflin-St Jeor is recommended)
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Enter your weight, height, and age
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View your BMR and daily calorie needs based on activity level
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Understanding the key inputs — BMR is the number of calories your body burns at complete rest, just to keep vital organs functioning
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Interpreting the results — multiply your BMR by the activity factor to get your Total Daily Energy Expenditure (TDEE) for weight planning
Examples
Good Examples
Average adult male (metric, Mifflin-St Jeor)
(10 × 70) + (6.25 × 170) - (5 × 30) + 5 = 1,680 calories/dayActive female daily needs
BMR 1,400 × 1.55 (moderate activity) = 2,170 calories/dayWeight loss planning
BMR 1,600 × 1.375 (light activity) = 2,200 TDEE; eating 1,700 cal/day creates a 500 cal deficit for ~1 lb/week lossComparing BMR equations
Mifflin-St Jeor and Harris-Benedict can differ by 100-200 calories — Mifflin is more accurate for most modern adultsBad Examples
Using BMR as total daily calories
BMR is only the minimum at rest — actual needs are higher based on activityMixing metric and imperial
Entering weight in kg but height in inches gives meaningless resultsEating below BMR for weight loss
Consistently eating below your BMR can slow metabolism and cause muscle loss — aim for a moderate deficit from TDEECommon Mistakes
- Confusing BMR with total daily calorie needs — BMR is the minimum at rest; multiply by activity factor for actual needs
- Not accounting for body composition — BMR formulas don't distinguish between muscle and fat mass
- Using the wrong equation — different equations may give different results; Mifflin-St Jeor is considered most accurate for most people
- Forgetting age factor — BMR decreases with age, so recalculate periodically
- Mixing unit systems — use either metric (kg, cm) or imperial (lbs, inches), not a mix
- Eating below BMR long-term — sustained very low calorie intake can reduce metabolic rate and lead to nutrient deficiencies
- Not adjusting for significant weight changes — if your weight changes by more than 5-10%, recalculate your BMR
- Treating BMR as exact — these are estimates based on population averages, and individual variation can be ±10-15%
Frequently Asked Questions
What is BMR?
Basal Metabolic Rate (BMR) is the number of calories your body needs to perform basic life-sustaining functions at rest, such as breathing, circulation, and cell production. It typically accounts for 60-75% of your total daily calorie expenditure.
What is the difference between BMR and TDEE?
BMR is the calories you burn at complete rest. TDEE (Total Daily Energy Expenditure) is BMR multiplied by an activity factor, representing your actual daily calorie needs. TDEE ranges from 1.2x BMR (sedentary) to 1.9x BMR (super active).
Which BMR formula is most accurate?
The Mifflin-St Jeor equation is considered the most accurate for most people. The original Harris-Benedict equation tends to overestimate BMR. The Harris-Benedict revised equation is a 1984 update that is closer to Mifflin-St Jeor.
Does muscle mass affect BMR?
Yes — muscle tissue burns more calories at rest than fat tissue. This is why athletes and people with higher muscle mass tend to have a higher BMR, even at the same weight. The standard BMR formulas do not account for body composition directly.
How to use BMR for weight loss planning?
Calculate your BMR, then multiply by your activity level to get your TDEE (Total Daily Energy Expenditure). To lose weight, eat 300-500 calories below your TDEE. Never eat below your BMR for extended periods, as your body needs at least that many calories for basic functions.
Mifflin-St Jeor vs Harris-Benedict — which BMR formula should I use?
The Mifflin-St Jeor equation is considered the most accurate for most people. The original Harris-Benedict equation tends to overestimate BMR by 5-10%. If you are very muscular or have an unusual body composition, consider using Katch-McArdle if you know your body fat percentage.
How does age affect my basal metabolic rate?
BMR naturally decreases with age, roughly 1-2% per decade after age 20, primarily due to loss of muscle mass and hormonal changes. A 20-year-old and a 60-year-old of the same height and weight can differ by 100-200 calories per day in BMR. Strength training can help slow this decline.
What is the difference between BMR and RMR (Resting Metabolic Rate)?
BMR is measured under strict conditions — after 8 hours of sleep and 12 hours of fasting in a lab. RMR is a more practical measurement taken under less restrictive conditions and is typically 10-20% higher than BMR. Most online calculators technically estimate RMR, though the terms are often used interchangeably.
How to increase my BMR naturally?
The most effective way to increase BMR is to build muscle through strength training, since muscle tissue burns more calories at rest than fat. Other strategies include staying hydrated, getting adequate sleep, eating enough protein (which has a higher thermic effect), and avoiding extreme calorie restriction that can lower BMR.