BMR Calculator
Calculate your Basal Metabolic Rate - the number of calories your body burns at complete rest to maintain vital functions.
BMR Calculation Formulas
Mifflin-St Jeor (Men)
Mifflin-St Jeor (Women)
What is Basal Metabolic Rate?
Basal Metabolic Rate (BMR) is the number of calories your body requires to perform its most basic life-sustaining functions while at complete rest. This includes breathing, circulating blood, cell production, nutrient processing, protein synthesis, and ion transport across cell membranes.
Your BMR represents approximately 60-75% of your total daily calorie expenditure. Understanding your BMR is fundamental to effective weight management because it establishes the baseline of calories you need just to exist - before accounting for any physical activity.
Scientific Accuracy
Uses three validated formulas for comprehensive BMR estimation across different body types.
Instant Results
Get your BMR calculation immediately with detailed breakdown by activity level.
Multiple Formulas
Compare results from Mifflin-St Jeor, Harris-Benedict, and Katch-McArdle equations.
Activity Multipliers
See estimated daily calorie needs for different activity levels based on your BMR.
Understanding the BMR Formulas
Several equations have been developed to estimate BMR, each with its own strengths and limitations:
Mifflin-St Jeor Equation (1990)
The most accurate for most adults according to research. Men: BMR = 10×weight(kg) + 6.25×height(cm) - 5×age + 5. Women: BMR = 10×weight(kg) + 6.25×height(cm) - 5×age - 161. Recommended by the Academy of Nutrition and Dietetics.
Harris-Benedict Equation (Revised 1984)
The classic formula, originally from 1919, revised for modern populations. Men: BMR = 13.4×weight(kg) + 4.8×height(cm) - 5.7×age + 88.4. Women: BMR = 9.2×weight(kg) + 3.1×height(cm) - 4.3×age + 447.6. Still widely used in clinical settings.
Katch-McArdle Equation
The only formula that accounts for body composition. BMR = 370 + (21.6 × lean body mass in kg). More accurate for athletic individuals or those with unusual body compositions, but requires knowing your body fat percentage.
BMR vs. RMR vs. TDEE
Understanding the differences between these related but distinct measurements is crucial:
| Metric | Measures | Conditions | Use Case |
|---|---|---|---|
| BMR | Minimum calories for vital functions | Complete rest, fasted, thermoneutral environment | Theoretical baseline for metabolism |
| RMR | Calories at rest (slightly higher than BMR) | Resting but less strict conditions | Practical clinical measurement |
| TDEE | Total daily calories including activity | Normal daily life | Actual calories needed per day |
Factors That Affect Your BMR
Many factors influence your basal metabolic rate, some you can control and others you cannot:
Muscle Mass
Muscle tissue burns more calories than fat tissue, even at rest. Each pound of muscle burns about 6 calories per day versus 2 for fat. This is why strength training can boost your metabolism.
Age
BMR decreases approximately 1-2% per decade after age 20, primarily due to muscle loss. Maintaining muscle through resistance training can partially offset this decline.
Genetics
Some people naturally have faster metabolisms due to genetic factors. This can account for 5-10% variation in BMR between individuals of similar size and composition.
Body Size
Larger bodies require more energy to maintain. Both height and weight contribute to higher BMR - there's simply more tissue to fuel.
Body Temperature
Fever increases BMR by about 7% for each degree Fahrenheit increase. Cold exposure can also temporarily boost metabolism through thermogenesis.
Hormones
Thyroid hormones significantly affect metabolic rate. Hypothyroidism slows metabolism, while hyperthyroidism speeds it up. Sex hormones also play a role.
Activity Multipliers Explained
To estimate your total daily calorie needs (TDEE), multiply your BMR by an activity factor:
| Activity Level | Multiplier | Description | Examples |
|---|---|---|---|
| Sedentary | 1.2 | Little or no exercise | Desk job, no regular exercise, mostly sitting |
| Lightly Active | 1.375 | Light exercise 1-3 days/week | Light walking, casual yoga, occasional gym |
| Moderately Active | 1.55 | Moderate exercise 3-5 days/week | Regular gym sessions, sports 3-5 times weekly |
| Very Active | 1.725 | Hard exercise 6-7 days/week | Daily intense workouts, athletic training |
| Extremely Active | 1.9 | Very hard exercise + physical job | Athletes, construction workers, multiple daily sessions |
How to Use Your BMR for Weight Goals
Understanding your BMR is the foundation for any weight management strategy:
Weight Maintenance
Eat calories equal to your TDEE (BMR × activity factor). Monitor weight weekly - if gaining, reduce slightly; if losing, increase slightly.
Weight Loss
Create a calorie deficit of 500-1000 calories below TDEE for 1-2 pounds of loss per week. Never eat below your BMR for extended periods - this can slow metabolism.
Weight/Muscle Gain
Eat 300-500 calories above TDEE. Combine with resistance training to ensure weight gained is primarily muscle rather than fat.
Never Go Below BMR
Eating fewer calories than your BMR is counterproductive and dangerous. It triggers metabolic adaptation, muscle loss, hormonal disruption, and often leads to weight regain.
Boosting Your Metabolism Naturally
While you can't dramatically change your BMR, these evidence-based strategies can help optimize your metabolic rate:
Build Muscle
Strength train 2-4 times weekly. More muscle mass directly increases BMR because muscle requires constant energy to maintain.
Eat Adequate Protein
Protein has a higher thermic effect (20-30%) than carbs (5-10%) or fat (0-3%). You burn more calories digesting protein. Aim for 0.7-1g per pound of bodyweight.
Prioritize Sleep
Sleep deprivation disrupts metabolic hormones. Aim for 7-9 hours. Poor sleep is linked to lower BMR and increased appetite.
Cold Exposure
Brief cold exposure activates brown fat and increases metabolic rate temporarily. Cold showers or lowering thermostat slightly may help.
Caffeine & Green Tea
Both can temporarily boost metabolism by 3-11%. The effect is modest but adds up over time when combined with other strategies.
Stay Hydrated
Drinking water can temporarily increase metabolic rate by 10-30% for about an hour. Cold water may be slightly more effective.
Frequently Asked Questions
Which BMR formula should I use?
For most people, the Mifflin-St Jeor equation is most accurate and is recommended by major nutrition organizations. If you know your body fat percentage and are athletic or have unusual body composition, the Katch-McArdle formula may be more accurate for you.
Why is my BMR different from online calculators?
Different calculators use different formulas. Some use the older Harris-Benedict equation, others use Mifflin-St Jeor. Our calculator shows multiple formulas so you can compare. The true test is tracking your calorie intake and weight changes over time.
Can I eat only my BMR calories to lose weight?
No, you should never eat at or below your BMR for extended periods. Eating at BMR means zero calories for activity, which causes extreme fatigue, muscle loss, and metabolic slowdown. Calculate your TDEE and eat 500-750 calories below that instead.
Does metabolism slow with age?
Yes, BMR decreases about 1-2% per decade after 20. However, research shows this is largely due to muscle loss, not aging itself. Maintaining muscle through resistance training can significantly minimize this decline.
Can I permanently increase my BMR?
The most effective way is building muscle mass through consistent strength training. Each pound of muscle burns about 6 calories per day. Gaining 10 pounds of muscle could increase daily burn by 60 calories - modest but meaningful over time.
Why do men have higher BMR than women?
Men typically have more muscle mass and less body fat than women of similar weight, and muscle is more metabolically active. Men are also generally larger. Additionally, testosterone supports higher metabolic rate.
How accurate are BMR calculators?
Population-based formulas are typically accurate within ±10% for most people. Individual variation depends on genetics, body composition, and health factors not captured by basic metrics. Use calculated BMR as a starting point and adjust based on real-world results.
Does eating small frequent meals boost metabolism?
No. Research shows meal frequency doesn't significantly affect metabolism. What matters is total daily calories and macronutrients, not when or how often you eat. Choose a meal pattern that helps you maintain consistent intake.
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