BMR Calculator

Welcome to the BMR Calculator, a comprehensive tool for estimating your Basal Metabolic Rate (BMR) and Resting Metabolic Rate (RMR) — 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 a 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:

BMR vs RMR: Are They the Same?

Basal Metabolic Rate (BMR) and Resting Metabolic Rate (RMR) are closely related but not identical. Both estimate the calories your body burns at rest, and in everyday use the terms are often used interchangeably — but they differ in how strictly they are measured:

• BMR is measured under very strict conditions: after roughly 8 hours of sleep, a 12-hour fast, lying completely still in a thermoneutral room, immediately upon waking. It represents the absolute energy floor.
• RMR is measured under more relaxed conditions (no overnight fast or sleep study required — just quiet rest). Because it captures a little residual digestion and minor movement, RMR is typically about 10% higher than BMR.

Importantly, the Mifflin-St Jeor and Harris-Benedict equations do not have a separate "RMR mode" — each outputs a single resting value. In fact, the Mifflin-St Jeor equation was derived from resting metabolic rate measurements, which is why the American Dietetic Association recommends it as the best predictor of RMR. This calculator reports your BMR from the chosen equation and also shows an estimated RMR ≈ BMR × 1.1, so you can use whichever figure your nutrition or fitness program references.

What Factors Affect 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

1. Enter your body metrics: Select your gender, enter age, weight, and height. Toggle between Imperial (lbs, ft/in) and Metric (kg, cm).
2. Select your activity level: Choose the level that best matches your typical weekly activity.
3. Choose a formula: Mifflin-St Jeor is recommended for most people; Harris-Benedict is available for comparison.
4. 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.

Is RMR the same as BMR?

Not exactly. BMR (basal metabolic rate) is measured under strict conditions — after an overnight fast and full rest — while RMR (resting metabolic rate) is measured under more relaxed conditions and runs about 10% higher. The Mifflin-St Jeor and Harris-Benedict equations estimate a single resting value, so this calculator shows your BMR and an estimated RMR of about BMR × 1.1. For most everyday planning the two numbers are used interchangeably.

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

• Basal Metabolic Rate - Wikipedia
• Harris-Benedict Equation - Wikipedia