WHAT IS BMR?
Basal Metabolic Rate (BMR) is the number of calories your body needs to perform basic life-sustaining functions. These include breathing, circulation, cell production, nutrient processing, and protein synthesis. In simpler terms, it's how many calories you'd burn if you stayed in bed all day doing absolutely nothing.
BMR typically accounts for about 60-70% of total daily calorie expenditure, making it the largest component of your metabolism. Understanding your BMR is crucial for setting accurate calorie targets, whether you're trying to lose weight, gain muscle, or maintain your current physique.
The Three BMR Formulas Explained
Mifflin-St Jeor Equation (Recommended)
Developed in 1990, this is considered the most accurate formula for most people. It accounts for modern lifestyles and body compositions better than older equations.
Men: BMR = (10 × weight) + (6.25 × height) - (5 × age) + 5
Women: BMR = (10 × weight) + (6.25 × height) - (5 × age) - 161
Harris-Benedict Equation (Revised)
Originally created in 1918 and revised in 1984, this classic formula tends to overestimate BMR slightly, especially for overweight individuals.
Men: BMR = 88.362 + (13.397 × weight) + (4.799 × height) - (5.677 × age)
Women: BMR = 447.593 + (9.247 × weight) + (3.098 × height) - (4.33 × age)
Katch-McArdle Equation
This formula uses lean body mass instead of total weight, making it more accurate for lean individuals who know their body fat percentage. It doesn't account for gender since it uses lean mass directly.
BMR = 370 + (21.6 × lean body mass in kg)
Which Formula Should You Use?
| Situation | Best Formula |
|---|---|
| Average person, general use | Mifflin-St Jeor |
| Lean athletes who know body fat % | Katch-McArdle |
| Historical comparison or research | Harris-Benedict |
| Obese individuals | Mifflin-St Jeor |
Factors That Affect Your BMR
Age
BMR decreases by about 2% per decade after age 20, primarily due to loss of muscle mass.
Muscle Mass
Muscle burns more calories than fat at rest. More muscle = higher BMR.
Gender
Men typically have 10-15% higher BMR due to greater muscle mass and lower body fat.
Body Size
Larger bodies require more energy to maintain basic functions, even at rest.
Genetics
Some people naturally have faster or slower metabolisms due to genetic factors.
Hormones
Thyroid hormones significantly impact metabolism. Conditions like hypothyroidism can lower BMR.
BMR vs RMR: The Difference
You might also see the term RMR (Resting Metabolic Rate). While often used interchangeably, there's a subtle difference:
BMR
Measured in a completely fasted state (12+ hours), after 8 hours of sleep, in a temperature-controlled room. Represents the absolute minimum energy needs.
RMR
Measured under less restrictive conditions. Typically 10-20% higher than BMR. More practical for everyday use.
For practical purposes, the difference is minimal. Our calculator estimates BMR, which gives you a conservative baseline.
How to Use Your BMR Results
Your BMR alone isn't very useful for setting calorie targets because it doesn't account for any movement or activity. Here's what to do with your BMR:
Calculate Your TDEE
Multiply BMR by an activity factor (1.2-1.9) to get your Total Daily Energy Expenditure. Use our TDEE Calculator for this.
Set Your Floor
Never eat below your BMR for extended periods. This can cause metabolic adaptation and muscle loss.
Track Changes
Recalculate periodically as you gain muscle, lose fat, or age. Your BMR changes with your body composition.
Can You Increase Your BMR?
While you can't dramatically change your metabolism, these factors can help increase BMR:
Each kg of muscle burns about 13 calories/day at rest vs 4.5 for fat.
Regular exercise helps maintain muscle mass and can slightly elevate resting metabolism.
Protein has a higher thermic effect and supports muscle maintenance.
Poor sleep can reduce BMR and disrupt hormones that regulate metabolism.
Frequently Asked Questions
Why is my BMR so high/low?▼
BMR varies significantly based on body size, age, gender, and muscle mass. A tall, muscular 25-year-old man might have a BMR of 2000+ calories, while a petite 50-year-old woman might be around 1200. Both can be perfectly healthy.
Can I eat below my BMR to lose weight faster?▼
While you can technically create a larger deficit, eating below BMR for extended periods can cause metabolic adaptation, muscle loss, nutritional deficiencies, and hormonal disruption. It's not recommended without medical supervision.
Does BMR decrease when dieting?▼
Yes, both from losing body mass (less tissue to maintain) and from metabolic adaptation (your body becomes more efficient). This is why periodic diet breaks and maintaining muscle through protein and resistance training are important.
How accurate are BMR calculators?▼
Formula-based BMR estimates are typically within 10% of measured values for most people. For precise measurement, you'd need indirect calorimetry in a clinical setting. For practical purposes, calculator estimates provide a good starting point.