BMR Calculator
Calculate Basal Metabolic Rate
3 formula options
Activity level TDEE
Detailed breakdown
Calories per hour
Even if you stayed in bed all day—no movement, no eating, no thinking hard—your body would still burn calories. Your heart beats. Your lungs breathe. Your cells repair themselves. That baseline energy burn is your Basal Metabolic Rate.
BMR is the foundation of all calorie calculations. Understanding it reveals how much fuel your body needs just to exist, before adding activity, exercise, or the energy cost of digesting food.
What is BMR?
Basal Metabolic Rate (BMR) is the number of calories your body burns at complete rest to maintain vital functions: breathing, circulation, cell production, and temperature regulation. It represents 60-75% of your total daily energy expenditure.
The Mifflin-St Jeor Formula (most accurate for most people):
Men: BMR = (10 Ă— weight kg) + (6.25 Ă— height cm) - (5 Ă— age) + 5
Women: BMR = (10 Ă— weight kg) + (6.25 Ă— height cm) - (5 Ă— age) - 161
BMR is at complete rest. RMR (Resting Metabolic Rate) is similar but measured under less strict conditions. TDEE (Total Daily Energy Expenditure) is BMR plus all daily activity.
Why People Actually Need This Tool
You can't understand your calorie needs without knowing BMR. It's the foundation for calculating how much to eat for any goal.
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Calorie planning — Establish the baseline for all diet calculations.
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Metabolic health assessment — Understand if your metabolism is typical or unusual.
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Weight plateau analysis — Check if calorie targets are actually below TDEE.
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Extreme diet prevention — Never eat below BMR for extended periods.
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Activity factor comparison — See how much exercise adds to your baseline.
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Formula comparison — Compare different BMR equations for your body type.
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Medical baseline — Establish metabolic baseline for health discussions.
How to Use the BMR Calculator
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Enter your stats — Age, gender, height, weight.
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View BMR — See your basal metabolic rate in calories.
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Compare formulas — See results from different calculation methods.
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View TDEE estimates — BMR multiplied by activity factors.
| Formula | Best For | Notes |
|---|---|---|
| Mifflin-St Jeor | Most people | Most accurate for average body composition |
| Harris-Benedict | Historical comparison | Older formula, tends to overestimate |
| Katch-McArdle | Athletes/lean individuals | Requires body fat percentage |
BMR formulas estimate averages. Your actual BMR could be 10-15% higher or lower due to genetics, thyroid function, and body composition.
Real-World Use Cases
1. The Minimum Calorie Floor
Context: Person trying aggressive weight loss considering 1,000-calorie diet.
Problem: Is 1,000 calories dangerously low?
Solution: Calculate BMR: 1,450 calories. 1,000 is well below BMR—not sustainable.
Outcome: Set minimum at BMR level. Sustainable deficit above that.
2. The Plateau Investigation
Context: Weight loss stalled at 1,200 calories for 5'2" woman.
Problem: Should she eat even less?
Solution: BMR: 1,280 calories. She's already below BMR—metabolism may be adapting.
Outcome: Increase calories slightly, add movement. Break plateau without restriction.
3. The Athletic Baseline
Context: Competitive swimmer training 3 hours daily needs calorie guidance.
Problem: How much to eat to maintain performance?
Solution: BMR: 1,600. TDEE with activity: 3,200+. Need to eat to train.
Outcome: Appropriate fueling for high-volume training.
4. The Reverse Diet Plan
Context: After years of dieting, person's metabolism feels "broken."
Problem: Eating 1,100 calories but not losing weight.
Solution: BMR: 1,400. Slowly increase to BMR level first, then above.
Outcome: Metabolic recovery plan based on BMR as target.
5. The Age Comparison
Context: 45-year-old feeling like metabolism has "slowed."
Problem: How much has BMR actually changed since age 25?
Solution: Calculate both: BMR at 25: 1,580. BMR at 45: 1,480. Only 100 calorie difference.
Outcome: Metabolism hasn't crashed. Activity levels likely decreased more.
6. The Body Composition Factor
Context: Muscular person with same weight as sedentary person.
Problem: Should they have the same BMR?
Solution: Use Katch-McArdle with body fat %. Muscle burns more than fat.
Outcome: More accurate BMR for athletic body composition.
7. The Medical Discussion
Context: Patient feels metabolism is abnormally slow.
Problem: Is this true or perception?
Solution: Calculate expected BMR. Compare to any metabolic testing results.
Outcome: Baseline for discussing potential thyroid or metabolic issues with doctor.
Common Mistakes and How to Avoid Them
BMR is what you burn at complete rest. You need TDEE (BMR Ă— activity) as your actual baseline. Don't eat at BMR unless bedridden.
Privacy and Data Handling
This BMR Calculator operates entirely in your browser.
- No body measurements are sent to any server.
- No health data is stored.
- No account required.
- Works completely offline.
Your personal health information stays private.
Conclusion
BMR is the metabolic foundation—the calories your body demands just to exist. Every calorie calculation builds from this baseline. Understanding BMR helps you set realistic goals and avoid the trap of extreme restriction.
This calculator provides your BMR using validated formulas, with activity multipliers to estimate TDEE. Know your baseline, plan accordingly, and respect what your body needs to function.
You can't outrun your metabolism. But you can understand it.