BMR Calculator

Calculate your Basal Metabolic Rate (BMR) — the calories your body burns at rest — using the Mifflin-St Jeor equation.

What Is Basal Metabolic Rate

Basal Metabolic Rate represents the number of calories your body burns at complete rest to maintain vital functions including breathing, blood circulation, cell production, nutrient processing, and temperature regulation. BMR accounts for 60 to 75 percent of total daily energy expenditure for most people. It is influenced by age, gender, height, weight, and body composition. Muscle tissue burns more calories at rest than fat tissue, which is why body composition significantly affects metabolic rate.

BMR Calculation Methods

Our calculator uses the Mifflin-St Jeor equation, which research has shown to be the most accurate prediction formula for most adults. It was developed in 1990 and accounts for the secular trend toward lower metabolic rates compared to older equations. The formula produces different results for men and women due to differences in average body composition. For individuals with significantly above or below average muscle mass, the Katch-McArdle formula using lean body mass may be more accurate.

Using BMR for Nutrition Planning

Your BMR is the foundation for calculating total daily energy expenditure by applying an activity multiplier. Never eat below your BMR for extended periods as this can trigger metabolic adaptation, muscle loss, and nutritional deficiencies. Use BMR as a minimum intake floor and calculate your actual needs using our Calorie Calculator which applies appropriate activity factors. Understanding your BMR helps you set realistic calorie targets for weight management goals.

Factors That Affect BMR

Several factors influence your basal metabolic rate beyond the standard formula inputs. Muscle mass is the most significant modifiable factor because muscle tissue requires more energy at rest than fat tissue. This is why resistance training can increase BMR over time. Genetics account for approximately 5 to 10 percent variation between individuals of similar size. Hormonal conditions particularly thyroid function significantly impact metabolic rate. Age-related BMR decline of 1 to 2 percent per decade is largely attributable to muscle loss, which can be partially offset through regular strength training.

Frequently Asked Questions

What is BMR and why does it matter?

Basal metabolic rate is the number of calories your body burns at complete rest to keep essential functions running, such as breathing, circulation, and cell repair. It represents the minimum energy you need each day before any activity. BMR matters because it forms the foundation of your total daily energy needs; once you know it, you can layer activity on top to estimate how much you should eat to maintain, lose, or gain weight. It typically accounts for the majority of the calories most people burn in a day.

How is BMR calculated?

This calculator uses the Mifflin-St Jeor equation, widely regarded as one of the more accurate formulas for estimating BMR. It combines your weight, height, age, and sex to produce an estimate, because each of these factors influences resting energy use. Muscle mass, which the formula does not measure directly, also affects metabolism, so the result is a well-supported estimate rather than an exact measurement. For a precise figure, clinical methods such as indirect calorimetry would be required.

What is the difference between BMR and TDEE?

BMR is the energy you burn at rest, while total daily energy expenditure (TDEE) adds the calories burned through movement, exercise, and digestion. TDEE is calculated by multiplying BMR by an activity factor that reflects how active you are. For everyday calorie planning, TDEE is the more practical number, but it is built directly on top of your BMR, which is why an accurate BMR estimate is the essential first step.

Why does BMR decrease with age?

Resting metabolism tends to decline gradually with age, largely because people often lose muscle mass and gain fat over the years, and muscle burns more energy at rest than fat does. Hormonal changes also play a role. This is one reason maintaining the same diet over decades can lead to slow weight gain. Staying active and preserving muscle through resistance training can help counteract some of this age-related decline.

Can I use my BMR to lose weight?

BMR is a starting point, not a target intake. To lose weight safely, you generally need a moderate calorie deficit relative to your TDEE, not your BMR. Eating only at your BMR level for an extended period is usually too restrictive and can be counterproductive. Use the BMR figure to build a realistic TDEE, then create a sensible deficit, and consider consulting a healthcare professional or dietitian for personalised guidance.