BMR Calculator
Calculate your Basal Metabolic Rate — the calories your body burns at complete rest — using three validated formulas side by side.
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Quick answer
BMR (Basal Metabolic Rate) is the number of calories your body burns at complete rest just to stay alive — typically 60–75% of total daily calories burned. It is most commonly estimated with the Mifflin-St Jeor equation.
- BMR is not a calorie target — it is the baseline used to calculate TDEE.
- Lean body mass is the single biggest driver of BMR.
Quick summary: BMR (Basal Metabolic Rate) is the energy your body needs just to stay alive at complete rest — breathing, circulation, cell repair, brain function. It typically accounts for 60–75% of total daily calories burned. Multiply BMR by an activity factor to get TDEE, the number to actually plan a diet around.
What BMR actually measures
Basal Metabolic Rate is the minimum number of calories your body needs over 24 hours to keep essential functions running while lying still, awake, and fasted — it does not include digestion, movement, or exercise. It is closely related to (and often used loosely interchangeably with) Resting Metabolic Rate (RMR), which is measured under slightly less strict lab conditions and runs a little higher.
BMR is driven mainly by lean body mass, followed by age, sex, and body size — muscle tissue burns more calories at rest than fat tissue, which is why two people of the same weight can have meaningfully different BMRs.
How this calculator works
Enter your basic stats to see BMR calculated three ways:
The three formulas compared
- Mifflin-St Jeor (1990): 10×weight(kg) + 6.25×height(cm) − 5×age + (5 for men, −161 for women). Generally the most accurate for the general population.
- Harris-Benedict (revised 1984): An older formula, still widely cited, that tends to run slightly higher than Mifflin-St Jeor for most people.
- Katch-McArdle: 370 + 21.6 × lean body mass (kg). More accurate for lean or very muscular individuals because it uses actual lean mass instead of estimating it from height/weight/age.
Worked example
A 28-year-old man, 175 cm, 72 kg: Mifflin-St Jeor BMR = 10×72 + 6.25×175 − 5×28 + 5 = 720 + 1,093.75 − 140 + 5 ≈ 1,679 kcal/day. With 20% body fat (57.6 kg lean mass), Katch-McArdle gives 370 + 21.6×57.6 ≈ 1,614 kcal/day.
BMR vs. related terms
| Term | What it measures | Typical relation |
|---|---|---|
| BMR | Calories at complete rest, strict fasted conditions | Baseline, usually the lowest figure |
| RMR | Calories at rest, less strict conditions | Usually 5–10% higher than BMR |
| TDEE | BMR/RMR × activity level | 1.2×–1.9× BMR depending on activity |
Which formula should you trust
The three formulas usually land within a few percent of each other, but pick the one that fits your situation:
- Use Mifflin-St Jeor as your default if you don't know your body fat percentage — it's the most validated formula for the general population.
- Use Katch-McArdle if you know your body fat percentage and are lean or heavily muscled — it's built from lean mass directly and avoids the errors height/weight formulas make for athletic body types.
- Use Harris-Benedict mainly for cross-checking, or if a clinician or program you're following specifically references it — on its own it tends to run a little high for most people today.
- Don't average the three — pick the one that matches your situation rather than splitting the difference, since the formulas aren't designed to be blended.
Benefits and limitations
Benefits: gives a fast, free estimate of resting energy needs, and comparing formulas highlights how sensitive the estimate is to muscle mass. Limitations: all formulas are population averages; actual BMR can be affected by thyroid function, medications, pregnancy, and genetics, and can only be measured precisely with indirect calorimetry.
Expert tips
- If you know your body fat percentage, weight the Katch-McArdle result more heavily — it accounts for muscle mass directly.
- Don't eat at or below your BMR for extended periods; it's meant to represent resting need, not a safe daily minimum, since you also need energy for movement and digestion.
- Use BMR as an input to calculate TDEE, not as a calorie target on its own.
- Unexplained large shifts in resting metabolism are worth discussing with a doctor, especially alongside fatigue, weight change, or temperature sensitivity.
Common mistakes
- Treating BMR as a daily calorie target rather than a baseline for calculating TDEE.
- Ignoring body composition when comparing BMR between two people of similar weight.
- Assuming a single formula is exact rather than an estimate with a margin of error.
Glossary
- BMR
- Basal Metabolic Rate — calories burned at complete rest under strict conditions.
- RMR
- Resting Metabolic Rate — a similar, slightly higher measure taken under less strict conditions.
- Lean body mass
- Total body weight minus fat mass — muscle, bone, organs, and water.
- Indirect calorimetry
- A lab method that measures BMR directly from oxygen consumption and carbon dioxide production.
Basal Metabolic Rate (BMR): everything to know
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Definition
The minimum calories the body needs over 24 hours to sustain essential functions at complete rest, fasted and awake.
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Attributes
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Measurements
- Mifflin-St Jeor equation (1990)
- Harris-Benedict equation (revised 1984)
- Katch-McArdle equation (lean-mass based)
- Indirect calorimetry (lab gold standard)
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Comparisons
- BMR vs. RMR: RMR is measured under less strict conditions and runs 5–10% higher.
- BMR vs. TDEE: TDEE = BMR × an activity multiplier.
Frequently asked questions
BMR varies widely with age, sex, height, and weight, but commonly falls between 1,200–1,800 kcal/day for adult women and 1,500–2,200 kcal/day for adult men.
No. BMR is your resting energy need only. Your actual calorie target should be based on TDEE, which adds activity on top of BMR.
Mifflin-St Jeor is generally considered most accurate for the general population; Katch-McArdle can be more accurate if you know your body fat percentage, especially if you're lean or very muscular.
Building muscle through resistance training is the most reliable way to modestly increase resting metabolic rate over time, since muscle tissue burns more calories at rest than fat.
Extended calorie restriction can trigger metabolic adaptation, a partial, usually temporary, reduction in resting energy expenditure beyond what weight loss alone would predict.
Facts, regions & standards
- Aliases
- BMR, Basal metabolism
- Synonyms
- Resting energy expenditure (loosely)
- Units
- kcal/day, kJ/day
- Standards bodies
- https://en.wikipedia.org/wiki/Basal_metabolic_rate
- Relationships
- Component of TDEE, Closely related to RMR, Driven by lean body mass
Sources & references
- A new predictive equation for resting energy expenditure — American Journal of Clinical Nutrition
- Resting Metabolic Rate: Best Practices — National Institutes of Health (NIH)
Author & reviewer
Now find your full daily calorie need
BMR is only the resting baseline. Add your activity level to get TDEE — the number to actually plan meals or a deficit around.