BMR Calculator Online - 2026

What is BMR?

Your **Basal Metabolic Rate (BMR)** represents the absolute minimum amount of energy in calories your body needs to function while at complete rest. This energy is used to power vital life-sustaining processes such as breathing, blood circulation, cell production, and nutrient processing.

Think of BMR as your body's "idling speed." Even if you spent 24 hours in bed without moving a muscle, your body would still consume this specific number of calories just to keep your organs alive and your brain signaling.

Where does the energy go?

Many people assume that physical exercise is their primary calorie burner. In reality, for most adults, BMR accounts for **60% to 75%** of total daily energy expenditure. Typical organ-level energy distribution looks as follows:

Mifflin-St Jeor: The Industry Standard

This calculator utilizes the **Mifflin-St Jeor equation**, which was introduced in 1990 as a more accurate alternative to the older Harris-Benedict formula. Extensive clinical research has shown that it remains remarkably accurate for modern sedentary and active populations alike, with an error margin of less than 10% for most adults.

Metabolic Efficiency Tip

While you cannot significantly change the calorie demand of your vital organs, you can increase your BMR by increasing lean muscle mass. Muscle is five times more metabolically active than fat, meaning the more muscle you have, the higher your "idling speed" becomes.