BMR Calculator
Enter your age, sex, height, and weight to find your Basal Metabolic Rate using the gold-standard Mifflin-St Jeor equation. You also get your Total Daily Energy Expenditure for six activity levels, plus calorie targets for mild, moderate, and aggressive weight loss or gain. Metric and imperial units both supported.
Formula
Worked example
A 30-year-old male weighing 75 kg at 175 cm: BMR = 10(75) + 6.25(175) - 5(30) + 5 = 750 + 1093.75 - 150 + 5 = 1698.75 kcal/day (~1699 kcal). At a sedentary activity level (x1.2): TDEE = 1699 x 1.2 = 2039 kcal/day. For 0.5 kg/week loss: 2039 - 500 = 1539 kcal/day.
What is Basal Metabolic Rate (BMR)?
Your Basal Metabolic Rate is the number of calories your body needs to carry out its most basic, life-sustaining functions at complete rest, such as breathing, circulating blood, regulating body temperature, and running organ systems. It represents the floor of your energy needs, typically 60-75% of total daily expenditure for sedentary adults. BMR rises with more lean muscle mass, a taller frame, younger age, and male biological sex, all of which are captured by the Mifflin-St Jeor equation. It falls with age, lower muscle mass, and significant calorie restriction (metabolic adaptation). Understanding your BMR is the first step to setting accurate calorie targets for weight management, athletic performance, or clinical nutrition planning.
The Mifflin-St Jeor equation and why it is recommended
Developed by M. D. Mifflin and colleagues in 1990, the Mifflin-St Jeor equation was validated against indirect calorimetry measurements in a large, diverse adult sample. The American Dietetic Association concluded it is the most accurate predictive equation for non-obese and obese individuals alike. For men: BMR = 10 x weight (kg) + 6.25 x height (cm) - 5 x age + 5. For women: BMR = 10 x weight (kg) + 6.25 x height (cm) - 5 x age - 161. The older original Harris-Benedict equations (1919) tend to overestimate BMR by about 5%. This calculator also offers the revised Harris-Benedict (Roza & Shizgal, 1984) and the Katch-McArdle formula for those who know their body fat percentage, which can be more accurate for lean, athletic individuals.
TDEE: from BMR to real-world calorie needs
BMR only accounts for resting energy needs. Your Total Daily Energy Expenditure (TDEE) adds the calories you burn through daily movement, exercise, and the thermic effect of food. TDEE is calculated by multiplying your BMR by a Physical Activity Level (PAL) factor. A sedentary office worker uses a factor of 1.2, while someone training intensely every day might use 1.725 or higher. TDEE is your maintenance calorie intake: eating at this level keeps your weight stable. To lose weight, subtract 250-750 kcal/day from your TDEE (roughly 0.25-0.75 kg per week). To gain weight, add 250-500 kcal/day. The standard estimate is that a 7,700 kcal total deficit or surplus corresponds to roughly 1 kg of body weight change, though this varies by individual and macronutrient composition.
Limitations and practical use
All BMR formulas are statistical estimates. They carry an inherent margin of error of roughly 10-15% even under ideal measurement conditions. Individual factors that the equations cannot capture include thyroid function, gut microbiome composition, prior weight loss history, sleep quality, and medication use. Treat the result as a starting point rather than an exact prescription. Track your actual weight over 2-4 weeks at a target intake and adjust by 100-200 kcal if weight is not moving as expected. The Katch-McArdle formula reduces one source of error (body size vs. composition) but introduces another if your body fat estimate is imprecise. For clinical purposes such as critical care or bariatric planning, indirect calorimetry remains the gold standard.
Activity level multipliers (PAL)
| Activity level | Typical description | Multiplier |
|---|---|---|
| Sedentary | Desk job, little or no exercise | 1.2 |
| Light | Light exercise or sport 1-3 days/week | 1.375 |
| Moderate | Moderate exercise or sport 4-5 days/week | 1.465 |
| Active | Hard daily exercise or intense sport 3-4x/week | 1.55 |
| Very active | Intense sport 6-7 days/week | 1.725 |
| Extra active | Very intense daily training or physical job | 1.9 |
Multiply your BMR by the factor below to estimate your TDEE at each activity level.
Frequently asked questions
What is the difference between BMR and TDEE?
BMR (Basal Metabolic Rate) is the calories your body burns at complete rest to keep you alive, covering breathing, circulation, and organ function. TDEE (Total Daily Energy Expenditure) adds the calories you burn through movement, exercise, and digesting food. TDEE is always higher than BMR and is the practical number to use for setting calorie intake targets.
Why does sex affect BMR?
Males typically have more lean muscle mass per unit of body weight than females of the same height and weight. Muscle tissue is metabolically more active than fat tissue, so it burns more calories at rest. The sex constants in the Mifflin-St Jeor formula (+5 for males, -161 for females) capture this average difference.
How accurate are BMR calculators?
Research shows that the Mifflin-St Jeor equation predicts measured BMR within 10% for most healthy adults. Individual results can be further off if you have unusual body composition, thyroid conditions, or have previously lost a significant amount of weight (which causes metabolic adaptation). Use the result as a starting estimate and adjust based on actual weight changes over 2-4 weeks.
Which BMR formula should I use?
Start with Mifflin-St Jeor: it is the most validated for general adults. If you have an accurate body fat percentage measurement, try Katch-McArdle, which can be more precise for lean or athletic individuals. The Revised Harris-Benedict is a reliable second option but generally less accurate than Mifflin-St Jeor for most people.
How many calories should I eat to lose weight?
A sustainable deficit is 300-500 kcal below your TDEE per day, producing roughly 0.3-0.5 kg of weight loss per week. Going below 1,200 kcal/day for women or 1,500 kcal/day for men is generally not recommended without medical supervision, as it risks nutrient deficiencies and muscle loss.
Does BMR change with age?
Yes. BMR declines by approximately 1-2% per decade from early adulthood onward, mainly because aging reduces lean muscle mass. Regular resistance training can slow this decline by preserving muscle tissue. The age term (-5 x age) in the Mifflin-St Jeor formula models this relationship.
Can I raise my BMR?
The most effective evidence-based strategy is building more lean muscle through resistance training. Muscle tissue burns roughly 13 kcal per kg per day at rest, compared to about 4 kcal per kg per day for fat tissue. Adequate sleep, avoiding very low-calorie diets (which cause metabolic adaptation), and maintaining a healthy thyroid function also help keep BMR from dropping.
Sources
- Mifflin MD et al. (1990), A new predictive equation for resting energy expenditure in healthy individuals. American Journal of Clinical Nutrition
- Roza AM, Shizgal HM (1984), The Harris Benedict equation reevaluated: resting energy requirements and the body cell mass. American Journal of Clinical Nutrition