BMR Calculator
Compare your Basal Metabolic Rate across three science-backed formulas
Your BMR Results
Formula Breakdown
How each equation calculates your BMR
Understanding Basal Metabolic Rate
Basal Metabolic Rate (BMR) is the number of calories your body requires each day to maintain basic life-sustaining functions while completely at rest. These functions include breathing, blood circulation, cell production, nutrient processing, and temperature regulation. BMR typically accounts for 60 to 75 percent of your total daily calorie expenditure, making it by far the largest contributor to how much energy you burn. Even if you spent the entire day lying motionless, your body would still consume this baseline amount of energy just to keep you alive.
Several factors influence your BMR, with lean body mass being the most significant. Muscle tissue is metabolically active and burns more calories at rest than fat tissue. This explains why two people of identical weight can have notably different BMRs if one has more muscle mass. Age also plays a role because muscle mass naturally declines after the age of 30, gradually reducing BMR by roughly 1 to 2 percent per decade. Gender, genetics, and hormonal status, particularly thyroid function, further modulate your metabolic rate.
This calculator presents three well-established formulas so you can compare estimates rather than rely on a single number. The Mifflin-St Jeor equation is recommended by the American Dietetic Association as the most accurate for most adults. The Harris-Benedict equation, revised in 1984, is historically significant and still widely used. The Katch-McArdle formula takes a different approach by incorporating lean body mass, which can produce a more accurate estimate if you know your body fat percentage. Comparing all three gives you a reliable range for your true resting metabolic rate.
Knowing your BMR is the first step in building an effective nutrition plan. To estimate your Total Daily Energy Expenditure (TDEE), multiply your BMR by an activity factor ranging from 1.2 for sedentary lifestyles to 1.9 for elite athletes. From there, you can set calorie targets for weight loss, maintenance, or muscle gain. Remember that BMR formulas provide estimates, not exact measurements. Use your result as a starting point and adjust based on how your body responds over two to four weeks of consistent tracking.
How to Use This Calculator
- Select your preferred unit system (Metric or Imperial) using the toggle at the top of the form. Input fields will update their placeholders and validation ranges automatically.
- Enter your age in years, your current body weight, and your height in the corresponding fields.
- Select your biological gender (male or female), which affects the Mifflin-St Jeor and Harris-Benedict calculations.
- Optionally enter your body fat percentage to enable the Katch-McArdle formula. If you don't know your body fat, simply leave this field blank.
- Click "Calculate BMR" to view your results from all applicable formulas, a visual comparison bar chart, and detailed formula explanations.
Frequently Asked Questions
What is the difference between BMR and TDEE?
BMR (Basal Metabolic Rate) measures the calories your body burns at complete rest to maintain vital functions like breathing and circulation. TDEE (Total Daily Energy Expenditure) includes your BMR plus all additional calories burned through daily activity, exercise, and digesting food. Your TDEE is always higher than your BMR. To calculate TDEE, multiply your BMR by an activity factor between 1.2 (sedentary) and 1.9 (extremely active).
Which BMR formula is the most accurate?
The Mifflin-St Jeor equation is considered the most accurate for the general population and is recommended by the American Dietetic Association. However, if you know your body fat percentage, the Katch-McArdle formula may be more accurate for you, especially if you are very lean or very muscular, since it directly accounts for lean body mass. The Harris-Benedict equation tends to slightly overestimate BMR, particularly in overweight individuals.
Why do the three formulas give different results?
Each formula was developed using different study populations and mathematical approaches. Mifflin-St Jeor and Harris-Benedict both use weight, height, age, and gender but with different coefficients, reflecting the data sets used in their original research. Katch-McArdle takes a fundamentally different approach by using lean body mass instead of total weight, ignoring gender entirely since lean mass already reflects body composition. Differences of 50 to 200 calories between formulas are normal and expected.
How do I estimate my body fat percentage?
There are several methods to estimate body fat percentage. The most accessible is visual comparison charts, which give a rough estimate by comparing your physique to reference images. Skinfold calipers, used by a trained professional, provide moderate accuracy at low cost. Bioelectrical impedance scales (BIA) are convenient but can vary with hydration. For the most accurate results, DEXA scans and hydrostatic weighing are considered gold standards. If you are unsure, most healthy males are between 10 and 25 percent and most healthy females between 18 and 35 percent body fat.
Does my BMR change as I age?
Yes. BMR typically declines with age, primarily because of the natural loss of lean muscle mass, a process called sarcopenia. After age 30, most people lose about 3 to 8 percent of muscle mass per decade. This gradual decline in metabolically active tissue reduces resting energy expenditure by approximately 1 to 2 percent every 10 years. Regular resistance training and adequate protein intake can slow this decline and help maintain a higher BMR well into older age.
Can I increase my BMR?
The most effective way to raise your BMR is to increase lean muscle mass through resistance training, since muscle burns more calories at rest than fat. Studies show that each pound of muscle burns roughly 6 to 7 calories per day at rest, compared to about 2 calories per pound of fat. Other factors that support a healthy metabolic rate include getting 7 to 9 hours of quality sleep, managing stress, eating adequate protein, and avoiding prolonged very-low-calorie diets, which can trigger metabolic adaptation and lower your BMR.
Should I eat exactly my BMR calories to lose weight?
No. Eating at or below your BMR for extended periods can slow your metabolism, lead to muscle loss, and cause nutrient deficiencies. For sustainable weight loss, you should eat above your BMR but below your TDEE, creating a moderate calorie deficit of 300 to 500 calories per day. This approach preserves lean muscle mass while still promoting fat loss at a rate of roughly 0.25 to 0.5 kilograms per week. Always consult a healthcare professional before starting a very low-calorie diet.
