BMR Calculator

Understanding Basal Metabolic Rate

Your body is never truly idle. Even while you sleep, your heart pumps, your lungs exchange oxygen, your cells rebuild, and your brain regulates temperature and hormones. Basal Metabolic Rate, or BMR, is the number of calories your body burns to perform these essential functions in a completely rested state. It represents the baseline energy cost of staying alive.

Because BMR typically makes up 60-75% of your total daily calorie burn, it is the single most important number to know when planning nutrition for weight loss, maintenance, or muscle gain. Your age, sex, weight, and height all influence it, which is why the Mifflin-St Jeor equation uses those four inputs to produce a reliable estimate.

How to Use This Calculator

Choose metric or imperial units, then enter your gender, age, weight, and height. The calculator applies the Mifflin-St Jeor formula instantly and shows your estimated BMR in calories per day. Below that, it multiplies your BMR by standard activity factors to give you a range of TDEE estimates, from sedentary to super active. There is no submit button; the numbers update as you type.

Worked Example

Imagine a 30-year-old man who weighs 80 kg and is 180 cm tall. Using the Mifflin-St Jeor equation, his BMR equals 10 × 80 + 6.25 × 180 − 5 × 30 + 5, which comes to 1,780 calories per day. If he is mostly sedentary, his estimated TDEE is about 2,135 calories. If he exercises moderately three to five times per week, his TDEE rises to roughly 2,760 calories. This is the practical bridge between BMR and real-world calorie targets.

Common Use Cases

• Meal planning: Build a daily menu around your TDEE target instead of guessing portion sizes.
• Weight loss: Create a safe calorie deficit, usually 300-500 calories below TDEE, while keeping intake near or above your BMR.
• Muscle gain: Add a small surplus above TDEE to support resistance training and recovery.
• Cross-checking apps: Compare the result against fitness trackers and diet apps that may use different equations.

Tips for Interpreting Your Result

• Treat BMR as an estimate, not a lab measurement. Individual variation in hormones, genetics, and body composition can shift the true value by about 10%.
• Recalculate whenever your weight changes significantly, your activity level shifts, or you pass a new decade in age.
• Pair BMR with waist circumference, progress photos, and strength benchmarks rather than relying on calories alone.
• Avoid prolonged diets below your BMR, which can increase fatigue, reduce muscle mass, and slow long-term weight loss.
• Include resistance training and enough protein to preserve lean mass, the main driver of a healthy metabolic rate.