Free BMR Calculator
Calculate your Basal Metabolic Rate — the calories your body burns at complete rest. Compare results from multiple validated formulas.
What is BMR (Basal Metabolic Rate)?
BMR (Basal Metabolic Rate) is the number of calories your body burns at complete rest just to maintain basic life functions. If you stayed in bed all day doing absolutely nothing, your body would still burn your BMR in calories to keep you alive.
Your BMR powers essential functions like:
- Breathing — Your lungs work 24/7
- Blood circulation — Your heart never stops pumping
- Cell production & repair — Your body constantly regenerates
- Brain function — Your brain uses about 20% of BMR
- Temperature regulation — Maintaining 98.6°F takes energy
- Hormone production — Endocrine system runs constantly
BMR typically accounts for 60-70% of your total daily calorie burn. Even the most active athletes burn more calories through BMR than through exercise.
BMR vs TDEE: What's the Difference?
Understanding the difference between BMR and TDEE is crucial for successful dieting:
| Aspect | BMR | TDEE |
|---|---|---|
| What it measures | Calories burned at complete rest | Total calories burned per day |
| Includes activity? | No | Yes |
| Includes food digestion? | No | Yes (TEF) |
| Use for diet planning? | As a floor (never go below) | Yes (subtract for deficit) |
| Typical value (avg adult) | 1,400-1,800 cal | 1,800-2,500 cal |
BMR Formulas Explained
Several validated equations exist for calculating BMR. Here's how they work:
🏆 Mifflin-St Jeor Equation (Recommended)
Developed in 1990, this is considered the most accurate for healthy adults[1]:
Men: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5 Women: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161 Why we recommend it: Multiple studies show it has the highest accuracy rate across different populations.
📜 Harris-Benedict Equation (Original)
The original BMR equation from 1918, revised in 1984:
Men: BMR = (13.397 × weight in kg) + (4.799 × height in cm) − (5.677 × age) + 88.362 Women: BMR = (9.247 × weight in kg) + (3.098 × height in cm) − (4.330 × age) + 447.593 Note: Tends to overestimate BMR by about 5% compared to Mifflin-St Jeor.
💪 Katch-McArdle Formula (Lean Mass Based)
The most accurate for lean individuals who know their body fat percentage:
BMR = 370 + (21.6 × lean body mass in kg) Lean body mass = total weight × (1 − body fat %)
Best for: Athletes, bodybuilders, and anyone who knows their body fat percentage.
What Affects Your BMR?
Many factors influence your basal metabolic rate:
Body Size & Composition
Larger bodies and those with more muscle mass burn more calories at rest. Muscle tissue is metabolically active, burning about 6 cal/lb/day.
Age
BMR decreases about 1-2% per decade after age 20, primarily due to muscle loss. Strength training can significantly slow this decline.
Gender
Men typically have higher BMR due to greater muscle mass and testosterone. The formulas account for these hormonal differences.
Genetics
Natural metabolic rate varies by 5-8% between individuals. Some people genuinely have "faster" or "slower" metabolisms.
Hormones
Thyroid hormones, testosterone, and growth hormone significantly impact BMR. Conditions like hypothyroidism can lower BMR by 30-40%.
Diet History
Chronic calorie restriction can temporarily lower BMR through metabolic adaptation. This reverses when eating at maintenance.
How to Increase Your BMR
While you can't change some factors (age, genetics), you can optimize others:
- Build muscle through strength training
Each pound of muscle burns about 6 calories per day at rest, compared to 2 calories for fat. Building 5-10 lbs of muscle can increase BMR by 30-60 calories daily.
- Eat adequate protein
Protein has a high thermic effect and supports muscle maintenance. Aim for 0.7-1g per pound of body weight. Calculate your protein needs →
- Don't crash diet
Extreme calorie restriction lowers BMR through metabolic adaptation. Stick to a moderate deficit (500 cal below TDEE).
- Get enough sleep
Sleep deprivation can reduce BMR and increase hunger hormones. Aim for 7-9 hours per night.
- Stay hydrated
Dehydration can slow metabolic processes. Drinking cold water may slightly increase BMR as your body warms it.
- Manage stress
Chronic stress elevates cortisol, which can promote fat storage and muscle breakdown over time.
Common BMR Mistakes
❌ Eating at or below BMR
Some people think eating at BMR will cause weight loss. This is dangerous — your body needs more than BMR just to function normally throughout the day. Eating too little causes metabolic slowdown, muscle loss, and hormonal issues.
❌ Confusing BMR with TDEE
BMR is your resting metabolism. TDEE is what you actually burn. A woman with a 1,400 BMR might have a 1,900 TDEE. Eating 1,400 calories would create too large a deficit.
❌ Trusting "metabolism boosting" supplements
Most metabolism boosters are ineffective or provide minimal benefit (maybe 50-100 extra calories). Focus on muscle building and adequate nutrition instead.
❌ Thinking BMR is fixed
Your BMR changes based on your weight, muscle mass, age, and dietary habits. Recalculate periodically as your body changes.
How Accurate is BMR Calculation?
BMR equations provide estimates, not exact values:
- Accuracy range: Within ±10% for most healthy adults
- Mifflin-St Jeor: Most accurate for the general population[1]
- Katch-McArdle: More accurate when body fat % is known
- For exact BMR: Indirect calorimetry testing is required (breathing into a machine)
Frequently Asked Questions
Everything you need to know about BMR
What is BMR?
BMR (Basal Metabolic Rate) is the number of calories your body burns at complete rest just to maintain vital functions like breathing, circulation, and cell production. It represents 60-70% of your total daily energy expenditure and is the minimum energy your body needs to survive.
What's the difference between BMR and TDEE?
BMR is the calories burned at complete rest, while TDEE (Total Daily Energy Expenditure) includes BMR plus all activity and the thermic effect of food. TDEE is always higher than BMR. Use TDEE for diet planning; BMR is the baseline your body needs to function.
Which BMR formula is most accurate?
The Mifflin-St Jeor equation is considered most accurate for most healthy adults according to research. If you know your body fat percentage, the Katch-McArdle formula may be more accurate as it's based on lean body mass.
Should I eat at my BMR to lose weight?
No, you should never eat at or below your BMR for extended periods. BMR represents the minimum calories for basic survival functions. Eating below BMR can slow metabolism, cause muscle loss, and harm health. Base your diet on TDEE instead — subtract 500 calories from TDEE for safe weight loss.
How do I increase my BMR?
Build more muscle through strength training — muscle tissue burns more calories at rest than fat tissue. Other factors include: staying hydrated, getting enough sleep, eating adequate protein, and avoiding extreme calorie restriction which can lower BMR.
Why is my BMR so low?
BMR is affected by: body size (smaller people have lower BMR), muscle mass (less muscle = lower BMR), age (BMR decreases with age), gender (women typically have lower BMR), and dieting history (chronic dieting can lower BMR). Genetics also plays a role.
Does metabolism slow with age?
Yes, BMR typically decreases about 1-2% per decade after your 20s. This is primarily due to loss of muscle mass, which can be significantly slowed through regular strength training and adequate protein intake.
How accurate is this BMR calculator?
Our calculator uses validated equations (Mifflin-St Jeor, Harris-Benedict, Katch-McArdle) that are accurate within 10% for most people. Actual BMR can vary due to genetics, hormones, and other factors. For precise measurement, indirect calorimetry testing is required.
References
- Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 1990;51(2):241-247. PubMed
- Frankenfield D, Roth-Yousey L, Compher C. Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults. J Am Diet Assoc. 2005;105(5):775-789. PubMed
- Harris JA, Benedict FG. A Biometric Study of Human Basal Metabolism. Proc Natl Acad Sci USA. 1918;4(12):370-373. PubMed
- McArdle WD, Katch FI, Katch VL. Exercise Physiology: Nutrition, Energy, and Human Performance. 8th ed. Wolters Kluwer; 2015.