BMR Calculator
Calculate your Basal Metabolic Rate (BMR) — the calories your body burns at rest — using Mifflin-St Jeor, Harris-Benedict, and Katch-McArdle formulas.
BMR formulas compared.
BMR is the amount of energy your body needs while completely at rest.
Male: 10W + 6.25H − 5A + 5
Female: 10W + 6.25H − 5A − 161
Understanding Basal Metabolic Rate (BMR)
Your Basal Metabolic Rate (BMR) represents the absolute minimum number of calories your body requires to perform life-sustaining functions while at complete rest. These essential processes include breathing, circulating blood, controlling body temperature, cell production, nutrient processing, and brain function. Even when you are sleeping or completely inactive, your organs require a continuous supply of energy to survive. BMR typically accounts for 60% to 75% of your total daily energy expenditure, depending on your lifestyle and body composition.
How BMR is Determined Mathematically
The BMR Calculator calculates your metabolic rate using the Mifflin-St Jeor equation, which is widely recognized as the most accurate formula for healthy adults. The equation utilizes your height, weight, age, and biological sex, as these factors directly dictate metabolic activity. Men generally possess greater muscle mass and lower body fat percentages than women, leading to higher baseline caloric demands. Height and weight determine your overall surface area and mass, while age accounts for the gradual decline in metabolic efficiency that occurs as cellular turnover slows down over time.
Applying BMR to Weight Management Goals
To lose, maintain, or gain weight, your BMR serves as the starting foundation. By multiplying your BMR by an activity factor (using the Harris-Benedict equation multipliers), you determine your Total Daily Energy Expenditure (TDEE). Eating fewer calories than your TDEE creates a caloric deficit leading to weight loss, while consuming more creates a surplus for weight gain. Knowing your baseline metabolic requirements ensures you do not restrict calories below safe physiological limits, preserving muscle mass and vital organ health.
Frequently Asked Questions
BMR is the number of calories your body burns at complete rest to maintain vital functions like breathing, circulation, and cell production. Knowing your BMR helps you set an accurate calorie baseline — whether your goal is weight loss, maintenance, or muscle gain.
This calculator uses the Mifflin-St Jeor equation, widely considered the most accurate for most adults. It calculates BMR as: (10 × weight kg) + (6.25 × height cm) − (5 × age) + 5 for males, and −10 for females. This formula was validated in a 2005 ADA study as more precise than the older Harris-Benedict formula.
BMR is the calories burned at rest with no activity at all. TDEE (Total Daily Energy Expenditure) multiplies your BMR by an activity factor (e.g., sedentary ×1.2, lightly active ×1.375) to estimate the total calories you actually burn in a day including movement, exercise, and digestion.
All four variables directly influence BMR. Taller and heavier individuals burn more calories at rest. BMR declines with age as muscle mass naturally decreases. Males typically have higher BMRs than females due to greater lean muscle mass and different hormonal profiles.
No. All calculations happen entirely inside your browser using JavaScript. No personal data, health inputs, or results are transmitted to any server. Your calculation history is saved only in your browser’s local storage and never leaves your device.