BMR Calculator
Calculate your Basal Metabolic Rate — the calories your body burns at complete rest. Compare results from Mifflin-St Jeor and Harris-Benedict equations.
Your BMR
1,699
calories/day at rest
Mifflin-St Jeor
1,699
Recommended
Harris-Benedict
1,763
Difference: 64 cal (3.7%)
Daily Calorie Needs by Activity Level
| Activity Level | Multiplier | Calories/day |
|---|---|---|
| Sedentary (little or no exercise) | ×1.2 | 2,039 |
| Lightly Active (exercise 1-3 days/week) | ×1.375 | 2,336 |
| Moderately Active (exercise 3-5 days/week) | ×1.55 | 2,633 |
| Very Active (exercise 6-7 days/week) | ×1.725 | 2,930 |
| Extremely Active (athlete/physical job) | ×1.9 | 3,228 |
How the BMR Calculator Works
This calculator uses two validated scientific formulas to estimate your resting metabolic rate. The Mifflin-St Jeor equation is considered the gold standard for accuracy in most adults, while Harris-Benedict provides a useful comparison point.
Mifflin-St Jeor Equation
Male: BMR = 10W + 6.25H − 5A + 5 Female: BMR = 10W + 6.25H − 5A − 161 W = Weight in kilograms
H = Height in centimeters
A = Age in years
Example Calculation
For a 28-year-old female, 65 kg, 165 cm:
- BMR = 10(65) + 6.25(165) − 5(28) − 161
- BMR = 650 + 1,031.25 − 140 − 161
- BMR = 1,380 calories/day
This means her body burns approximately 1,380 calories just to maintain basic functions at complete rest.
Tips for Using Your BMR
- Never eat below your BMR for extended periods
- Multiply BMR by your activity factor to get TDEE (total daily calories)
- Muscle mass increases BMR — prioritize strength training
- Crash diets can reduce BMR by 15-20% through metabolic adaptation
- Sleep deprivation reduces BMR — aim for 7-9 hours nightly
Frequently Asked Questions
What is the difference between Mifflin-St Jeor and Harris-Benedict equations?
The Mifflin-St Jeor equation (1990) is considered more accurate for modern populations. It typically estimates 5% lower than Harris-Benedict (1919). Mifflin-St Jeor: 10×weight + 6.25×height − 5×age ± constant. Harris-Benedict uses different coefficients and is slightly less accurate for obese individuals.
What is BMR and why does it matter?
BMR (Basal Metabolic Rate) is the number of calories your body burns at complete rest to maintain vital functions like breathing, circulation, and cell production. It accounts for 60-75% of your total daily calorie burn. Knowing your BMR helps you set accurate calorie targets for weight management.
How does age affect BMR?
BMR decreases by approximately 1-2% per decade after age 20. This happens due to loss of muscle mass (sarcopenia), hormonal changes, and reduced metabolic activity. A 50-year-old typically has a BMR about 200-300 calories lower than a 25-year-old of the same size. Regular strength training can slow this decline.
Does muscle mass increase BMR?
Yes. Muscle tissue burns about 6 calories per pound per day at rest, while fat burns only 2 calories per pound. Adding 10 pounds of muscle increases BMR by roughly 40-60 calories daily. This is why strength training is recommended for long-term metabolic health.
Can I eat below my BMR to lose weight faster?
Eating below your BMR is generally not recommended. It can cause muscle loss, nutrient deficiencies, metabolic adaptation (your body slows down), fatigue, and hormonal disruptions. A safe minimum is typically 1,200 calories for women and 1,500 for men, or no more than 20-25% below your TDEE.
How do I increase my metabolism?
Build muscle through resistance training (biggest impact), stay physically active throughout the day (NEAT), eat adequate protein (thermic effect of food), get 7-9 hours of sleep, stay hydrated, and avoid crash diets that cause metabolic adaptation. Consistency matters more than any single strategy.
Why do men have higher BMR than women?
Men typically have higher BMR because they carry more muscle mass and less body fat on average. Testosterone promotes muscle development, which is metabolically more active tissue. A man and woman of identical height and weight will still differ by about 5-10% in BMR due to body composition differences.