BMR Calculator
Calculate your BMR (basal metabolic rate) and daily calorie needs with the Mifflin-St Jeor and Harris-Benedict equations. Includes TDEE, activity-level breakdown, macronutrient estimates, and step-by-step formula walkthrough.
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About BMR Calculator
Welcome to the BMR Calculator, a comprehensive tool for estimating your Basal Metabolic Rate — the number of calories your body burns each day just to keep you alive. This calculator supports both the Mifflin-St Jeor equation (recommended for accuracy) and the classic Harris-Benedict equation, and provides your Total Daily Energy Expenditure (TDEE), macronutrient estimates, and step-by-step formula walkthrough.
What is BMR (Basal Metabolic Rate)?
Basal Metabolic Rate (BMR) is the minimum number of calories your body requires to perform essential life-sustaining functions while at complete rest. These include breathing, blood circulation, cell production, nutrient processing, and maintaining body temperature. BMR typically accounts for 60–75% of your total daily energy expenditure, making it the single largest component of your calorie burn.
Understanding your BMR is the foundation for any effective nutrition or fitness plan. It tells you the absolute minimum energy your body needs — eat below this consistently and you risk metabolic slowdown and muscle loss.
BMR Formulas Explained
Mifflin-St Jeor Equation (Recommended)
Published in 1990, this equation is considered the most reliable for modern populations. The American Dietetic Association recommends it as the best predictor of resting metabolic rate.
Harris-Benedict Equation (Original)
Originally published in 1919 and revised in 1984, this equation was the standard for decades. It tends to overestimate BMR by about 5% compared to measured values, but remains widely used.
BMR vs TDEE: What is the Difference?
BMR measures only calories burned at rest. TDEE (Total Daily Energy Expenditure) includes all calories burned throughout the day — BMR plus physical activity and the thermic effect of food. TDEE is calculated by multiplying BMR by an activity factor:
| Activity Level | Factor | Description |
|---|---|---|
| Sedentary | 1.2 | Little or no exercise, desk job |
| Lightly Active | 1.375 | Light exercise 1-3 days/week |
| Moderately Active | 1.55 | Moderate exercise 3-5 days/week |
| Very Active | 1.725 | Hard exercise 6-7 days/week |
| Extra Active | 1.9 | Very hard exercise & physical job |
What Factors Affect BMR?
Men typically have higher BMR due to greater muscle mass. Genetic factors can cause 10-15% variation between individuals of similar size.
BMR decreases approximately 1-2% per decade after age 20, primarily due to loss of lean muscle mass.
Muscle tissue burns more calories at rest than fat tissue. Higher muscle mass leads to higher BMR.
Extreme temperatures increase BMR as the body works harder to maintain core temperature. Cold exposure can raise BMR by 5-20%.
Thyroid hormones (T3, T4) significantly regulate metabolic rate. Hypothyroidism can lower BMR by 40%.
Larger bodies require more energy for basic functions. Taller and heavier individuals generally have higher BMR.
How to Use BMR for Weight Management
Weight Loss
To lose weight, consume fewer calories than your TDEE (not BMR). A safe calorie deficit is 500 calories below TDEE, leading to approximately 1 pound (~0.45 kg) of weight loss per week. Important: never eat below your BMR long-term, as this can trigger metabolic adaptation, muscle loss, and nutritional deficiencies.
Weight Gain
To gain weight (primarily muscle), consume 500 calories above TDEE combined with resistance training. This surplus supports muscle protein synthesis while limiting excess fat gain.
Weight Maintenance
Eat at your TDEE level to maintain your current weight. Track your actual weight over 2-3 weeks and adjust if needed, since calculated TDEE is an estimate.
How to Use This Calculator
- Enter your body metrics: Select your gender, enter age, weight, and height. Toggle between Imperial (lbs, ft/in) and Metric (kg, cm).
- Select your activity level: Choose the level that best matches your typical weekly activity.
- Choose a formula: Mifflin-St Jeor is recommended for most people; Harris-Benedict is available for comparison.
- Review your results: See your BMR, TDEE, calorie targets for weight loss/gain, macronutrient estimates, and step-by-step calculation.
Frequently Asked Questions
What is BMR (Basal Metabolic Rate)?
BMR is the number of calories your body needs to maintain basic life-sustaining functions at complete rest, such as breathing, blood circulation, cell production, and nutrient processing. It typically accounts for 60-75% of your total daily energy expenditure.
What is the difference between BMR and TDEE?
BMR measures calories burned at rest, while TDEE includes all calories burned through BMR plus physical activity and the thermic effect of food. TDEE = BMR × Activity Factor. TDEE is the number you should use when planning your diet and calorie intake.
Which BMR formula is more accurate: Mifflin-St Jeor or Harris-Benedict?
The Mifflin-St Jeor equation is generally considered more accurate for modern populations. A study published in the Journal of the American Dietetic Association found it to be the most reliable, predicting BMR within 10% of measured values for more individuals than other equations. The Harris-Benedict equation tends to overestimate BMR by about 5%.
How do I use BMR to lose weight?
To lose weight, consume fewer calories than your TDEE (not BMR). A safe deficit is 500 calories per day below TDEE, which leads to approximately 1 pound of weight loss per week. Never eat below your BMR, as this can slow metabolism and cause muscle loss.
What factors affect BMR?
Key factors include age (decreases 1-2% per decade after 20), gender (men have higher BMR), body composition (more muscle = higher BMR), height and weight, genetics, hormonal function (especially thyroid), and environmental temperature.
Additional Resources
Reference this content, page, or tool as:
"BMR Calculator" at https://MiniWebtool.com/bmr-calculator/ from MiniWebtool, https://MiniWebtool.com/
by miniwebtool team. Updated: Feb 06, 2026