BMR Calculator
Calculate your Basal Metabolic Rate using both the Mifflin-St Jeor and Harris-Benedict equations to see your resting calorie burn.
Results
Visualization
How It Works
Basal Metabolic Rate (BMR) is the number of calories your body needs to perform basic life-sustaining functions like breathing, circulation, and cell production while at complete rest. Two widely used formulas exist: the Mifflin-St Jeor equation (1990) and the revised Harris-Benedict equation (1984), with Mifflin-St Jeor generally considered more accurate for modern populations.
The Formula
Variables
- W — Body weight in kilograms
- H — Height in centimeters
- A — Age in years
Worked Example
A 30-year-old male, 70 kg, 170 cm: Mifflin = 10*70 + 6.25*170 - 5*30 + 5 = 1,618 kcal/day. Harris-Benedict = 88.362 + 13.397*70 + 4.799*170 - 5.677*30 = 88.362 + 937.79 + 815.83 - 170.31 = 1,672 kcal/day. The two formulas differ by about 54 kcal.
Practical Tips
- The Mifflin-St Jeor equation is recommended by the Academy of Nutrition and Dietetics as the most reliable for estimating BMR.
- BMR typically accounts for 60-75% of total daily calorie expenditure.
- Muscle tissue burns more calories at rest than fat tissue, so body composition affects BMR beyond what these formulas capture.
- Extreme calorie restriction can lower BMR by 15-20% through metabolic adaptation.
- Measure your weight in the morning before eating for the most consistent BMR calculation.
Frequently Asked Questions
Which BMR formula is more accurate?
The Mifflin-St Jeor equation, published in 1990, is considered more accurate for today's population. The original Harris-Benedict equation from 1919 (revised in 1984) tends to overestimate BMR by 5-15% in some groups.
Why do the two formulas give different results?
They were derived from different study populations and time periods. The Harris-Benedict equation was originally based on data from 1919, while Mifflin-St Jeor used a more modern and diverse sample. Differences are usually 50-200 calories.
Can I increase my BMR?
Building lean muscle through strength training is the most effective way to raise BMR. Each kilogram of muscle burns roughly 13 kcal/day at rest, compared to about 4.5 kcal/day for fat tissue. Regular exercise and adequate protein intake support muscle maintenance.
Does BMR decrease with age?
Yes, BMR typically declines 1-2% per decade after age 20, primarily due to loss of muscle mass. This is why calorie needs decrease with age, and why strength training becomes increasingly important for maintaining metabolism.
Is BMR the same as resting metabolic rate (RMR)?
They are similar but not identical. BMR is measured under strict conditions after 8 hours of sleep and 12 hours of fasting. RMR is measured under less restrictive conditions and is typically 10-20% higher than BMR. Most calculators estimate RMR and call it BMR.