BMR Calculator
Calculate your Basal Metabolic Rate using multiple scientific formulas. Find out how many calories your body burns at rest.
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How this calculator works
Mifflin-St Jeorv1.0.0
Resting metabolic rate from age, sex, height and weight. Default equation for general adults.
- Applies to
- Healthy adults; not validated for acute illness, very old/frail, or pregnancy
- Assumptions
- Sample of healthy adults; Resting, fasted conditions
- Limitations
- Individual RMR commonly varies ±10% around the estimate; Not a lab measurement
- Output
- kcal/day
- Last reviewed
- 2026-06-01
Harris-Benedict (revised, 1984)v1.0.0
Classic BMR equation, revised by Roza & Shizgal. Tends to read slightly higher than Mifflin-St Jeor.
- Applies to
- General adults
- Assumptions
- Same resting conditions as other BMR equations
- Limitations
- Overestimates by ~5% in many people compared with measured RMR
- Output
- kcal/day
- Last reviewed
- 2026-06-01
Katch-McArdlev1.0.0
BMR from lean body mass : the best choice when body fat percentage is known.
- Applies to
- Adults with known body composition
- Assumptions
- Accurate body fat measurement
- Limitations
- Sensitive to body-fat measurement error
- Output
- kcal/day
- Last reviewed
- 2026-06-01
Evidence Sources & Literature
- American Journal of Clinical Nutrition. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr, 1990. doi:10.1093/ajcn/51.2.241.
- American Journal of Clinical Nutrition. Harris Benedict equations reevaluated: resting energy requirements and body cell mass. Am J Clin Nutr, 1984. doi:10.1093/ajcn/40.1.168.
- Williams & Wilkins. Exercise Physiology: Energy, Nutrition and Human Performance (Katch-McArdle body-composition equation). Book, 1992.
About the BMR Calculator
Your BMR (basal metabolic rate) is the number of calories your body burns just to keep you alive at complete rest: breathing, circulating blood, maintaining temperature and running your organs. It is the foundation of your daily calorie needs, and understanding it is the first step in any sensible plan to lose, gain or maintain weight. This calculator estimates your BMR from your age, sex, height and weight.
I find BMR is one of the most clarifying numbers a person can know, because it shows just how many calories the body uses before you have moved a muscle on purpose. That tends to reframe how people think about food and activity in a healthier way.
What BMR includes
BMR is the energy your body spends at total rest to stay alive. Surprisingly, this baseline accounts for the majority of most people's daily calorie burn, often around 60 to 70 percent of the total. Your organs, particularly the brain, liver and heart, are working constantly, and that quiet, around-the-clock effort is what BMR captures.
How it is estimated
This calculator uses a well-validated equation (the Mifflin-St Jeor formula) that draws on your age, sex, height and weight. It is an estimate, not a lab measurement, but for everyday planning it is reliable and far more useful than guessing. Your real BMR varies a little with factors like muscle mass and genetics, which is why I treat the result as a strong starting point rather than an exact figure.
BMR versus total daily calories
BMR is not the same as how many calories you need in a day. To get your total (often called TDEE), you multiply BMR by an activity factor that accounts for movement, exercise and the energy used digesting food. So BMR is the floor, and your activity builds on top of it. If you want your full daily target, the TDEE calculator takes your BMR the rest of the way.
Why knowing it helps
Knowing your BMR keeps weight goals realistic. It explains why very low-calorie diets feel punishing and tend to backfire, since dropping far below your needs is hard to sustain and can reduce muscle. It also shows why building or keeping muscle helps, because muscle is metabolically active tissue. I use BMR with clients to set sensible calorie ranges rather than extreme ones.
Dietitian Insight: Your basal metabolic rate represents the resting energy needed to maintain vital organs. Learn how resting metabolism combines with movement in our BMR vs TDEE guide, or convert your baseline into full activity burns using our total daily energy expenditure calculator.
Sources & method
This calculator uses established, peer-reviewed formulas and reference ranges from recognized health and nutrition authorities. Results are estimates for general education, not a medical diagnosis. For decisions about your health, consult a qualified clinician. Reviewed by Macro & Meals Editorial Team, Content editor.
Frequently Asked Questions
What is BMR?
BMR (basal metabolic rate) is the number of calories your body burns at complete rest to keep you alive: breathing, circulating blood, maintaining temperature and running your organs. It typically accounts for around 60 to 70 percent of your total daily calorie burn.
How is BMR calculated?
This calculator uses the well-validated Mifflin-St Jeor equation, which draws on your age, sex, height and weight. It is an estimate rather than a lab measurement, but it is reliable enough for everyday planning and far better than guessing.
What is the difference between BMR and TDEE?
BMR is the calories you burn at rest, while TDEE (total daily energy expenditure) adds the calories used through movement, exercise and digestion. You get TDEE by multiplying BMR by an activity factor, so BMR is the foundation and TDEE is your full daily need.
Can I increase my BMR?
You have limited control, but building and keeping muscle helps because muscle is metabolically active tissue that burns more at rest than fat. Staying active and not under-eating for long periods also support a healthy metabolism. Dramatic, lasting changes to BMR are uncommon, so focus on sustainable habits.
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