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BMR Calculator

Find out how many calories your body needs at complete rest using the Mifflin-St Jeor equation. Includes BMR in kcal and kJ, organ-level breakdown, TDEE estimates, and age comparison.

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Height (cm)

Weight (kg)

What Is BMR?

Basal Metabolic Rate (BMR) is the number of calories your body needs at complete rest to maintain vital functions — breathing, circulation, cell production, nutrient processing, and temperature regulation.

BMR accounts for 60-75% of your total daily energy expenditure (TDEE). The remaining energy is used for physical activity (15-30%) and digesting food (10%).

Several factors influence BMR:

Muscle mass: More muscle increases BMR since muscle burns more calories at rest than fat.
Age: BMR decreases by 1-2% per decade after age 20 due to muscle loss.
Gender: Men typically have higher BMR than women due to greater muscle mass and body size.
Genetics: Some people naturally have faster or slower metabolisms.
Hormones: Thyroid hormones, cortisol, and sex hormones all affect metabolic rate.

The Mifflin-St Jeor Equation

Developed in 1990, the Mifflin-St Jeor equation is considered the most accurate formula for estimating BMR in the general population:

Male: BMR = 10 × weight(kg) + 6.25 × height(cm) - 5 × age + 5

Female: BMR = 10 × weight(kg) + 6.25 × height(cm) - 5 × age - 161

This formula has an accuracy of approximately ±10% compared to indirect calorimetry. It replaced the older Harris-Benedict equation, which tended to overestimate BMR by 5-15%.

Frequently Asked Questions

How is BMR different from TDEE?▾

BMR is what you burn at complete rest. TDEE (Total Daily Energy Expenditure) is BMR plus all your daily activity — walking, exercise, and digesting food. Use the activity-adjusted estimates above to see how your BMR translates to your total calorie needs.

Can I increase my BMR?▾

Yes, the most effective way is to increase muscle mass through resistance training. Each kilogram of muscle burns about 13 extra calories per day at rest. High-protein diets and adequate sleep also support a healthy metabolic rate.

Does eating less slow down my BMR?▾

Prolonged severe calorie restriction can lower BMR by 10-20% as the body adapts to conserve energy (metabolic adaptation). This is why moderate deficits of 300-500 calories are recommended for weight loss, and why refeed days or diet breaks can help maintain metabolic rate.

How often should I recalculate my BMR?▾

Recalculate whenever your weight changes by 5-10 lbs (2-5 kg) or your body composition changes significantly. Since BMR depends on weight, height, and age, you only need to recalculate when one of those factors changes.

What is the difference between BMR and RMR?▾

BMR (Basal Metabolic Rate) is measured under strict conditions — complete rest, after 8 hours of sleep, 12 hours of fasting. RMR (Resting Metabolic Rate) is measured under less strict conditions and is typically 5-10% higher than BMR. In practical use, the terms are often used interchangeably.

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How to Use This Tool

Enter your age, gender, height, and weight. Toggle between metric and imperial units as needed.
View your BMR in both kcal/day and kJ/day.
Explore the organ-level breakdown to see which body systems use the most energy.
Check the estimated TDEE for different activity levels to understand your total calorie needs.
Use the age comparison table to see how BMR changes over time.
Read the educational section and FAQs to learn how BMR affects your health and fitness.

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