BMR Calculator

Understanding Your Basal Metabolic Rate (BMR)

Your Basal Metabolic Rate (BMR) is the minimum amount of energy (calories) your body needs to maintain basic life-sustaining functions while at complete physical and mental rest in a temperate environment. These vital processes include breathing, blood circulation, temperature regulation, cell growth, brain function, and muscle contraction. Even if you spent the entire day in bed without moving a muscle, your body would still require these calories to survive.

Mifflin-St Jeor vs. Harris-Benedict Formulas

BMR calculators typically use one of two primary scientific formulas to estimate daily caloric requirements at rest:

• Mifflin-St Jeor Equation: Formulated in 1990, it is currently the industry standard recommended by the Academy of Nutrition and Dietetics. It has proven to be highly accurate for modern lifestyles and populations.
• Revised Harris-Benedict Equation: Originally published in 1918 and updated in 1984 by Roza and Shizgal. While older, it remains widely used but tends to slightly overestimate BMR compared to Mifflin-St Jeor.

How to Calculate BMR (Mifflin-St Jeor Formula)

The equations require your weight (in kilograms), height (in centimeters), age (in years), and biological sex:
For Men: BMR = (10 × weight in kg) + (6.25 × height in cm) - (5 × age in years) + 5
For Women: BMR = (10 × weight in kg) + (6.25 × height in cm) - (5 × age in years) - 161

Key Factors That Affect Your BMR

• Body Composition: Muscle tissue is much more active metabolically than fat tissue. Lean individuals with high muscle mass naturally have a higher BMR.
• Age: BMR generally decreases as you age due to natural loss of muscle mass and changes in hormonal activity.
• Biological Sex: Men typically have higher BMRs than women because they generally have more muscle mass and less body fat percentage.
• Genetics and Health: Thyroid hormones play a major role in regulating metabolic speed. Illnesses or fevers can also temporarily increase BMR.