BMR Calculator

Your Basal Metabolic Rate (BMR) is the number of calories your body needs to maintain basic functions — breathing, circulation, cell production — while completely at rest. It accounts for roughly 60–75% of total daily calorie burn for most people.

BMR is not the same as TDEE (Total Daily Energy Expenditure). Your TDEE includes the calories burned through daily movement and exercise on top of your BMR. Eating at your TDEE maintains your current weight; eating below it creates a deficit for weight loss.

This calculator uses the Mifflin–St Jeor equation, which is considered the most accurate formula for estimating BMR in most adults.

What is Basal Metabolic Rate (BMR)?

Your Basal Metabolic Rate is the number of calories your body needs each day to sustain essential functions while completely at rest — breathing, heartbeat, body temperature regulation, organ function, and cellular repair. It represents the minimum energy cost of staying alive and typically accounts for 60–75% of total daily calorie expenditure for most adults.

BMR is determined by factors including body size (larger bodies burn more calories), body composition (muscle burns more than fat at rest), age (BMR declines approximately 2–3% per decade after age 20 due to muscle loss), sex (men typically have higher BMRs due to greater muscle mass), and genetics. You cannot change your age or genetics, but you can meaningfully influence your BMR by building muscle through resistance training.

This calculator uses the Mifflin–St Jeor equation (1990), the most validated BMR formula for the general population. It is preferred over the older Harris-Benedict equation in most clinical and research contexts because it more accurately reflects actual resting metabolic rates measured in laboratory studies.

BMR vs TDEE: what is the difference?

BMR is your calorie floor — the minimum your body needs at complete rest. TDEE (Total Daily Energy Expenditure) is the actual number of calories you burn in a typical day, which includes your BMR plus all additional energy used for movement, digestion, and exercise. TDEE is what you should base your calorie intake on, not BMR.

For most people, TDEE is 20–90% higher than BMR depending on activity level. A sedentary office worker might have a TDEE that is 20% above BMR, while an athlete in heavy training might burn nearly twice their BMR in a day. Choosing the correct activity multiplier is critical for an accurate TDEE estimate.

Eating at your TDEE maintains your current weight. Eating below TDEE creates a deficit for weight loss. Eating above TDEE creates a surplus for muscle gain. Use our calorie deficit calculator to translate your TDEE into a specific weight loss target.

Frequently asked questions about BMR

Why is my BMR higher or lower than I expected?

BMR varies significantly between individuals of the same height and weight. The largest variable is body composition — a person with more muscle mass has a meaningfully higher BMR than someone of the same weight but higher body fat. Age is also a significant factor; BMR decreases with age as muscle mass naturally declines unless actively maintained through exercise.

Can I increase my BMR?

Yes — the most effective way is to build lean muscle mass through progressive resistance training. Each pound of muscle burns approximately 6 calories per day at rest, compared to about 2 calories for fat tissue. While this difference seems small, accumulating several pounds of muscle over months of training can increase your BMR by 50–100 calories per day — meaningful for long-term weight management.

Does dieting lower my BMR?

Yes, to some extent. When you restrict calories for an extended period, your body reduces energy expenditure beyond what would be expected from weight loss alone — a phenomenon called metabolic adaptation or adaptive thermogenesis. This is why very low calorie diets often produce disappointing long-term results. Maintaining adequate protein intake, including resistance training, and taking occasional diet breaks help minimise this effect.

How accurate is this BMR calculation?

The Mifflin–St Jeor equation estimates BMR with a margin of error of approximately ±10% compared to laboratory measurement. For most people it is accurate to within 100–200 calories per day. Use it as a starting point, track your actual results over 2–4 weeks of consistent eating, and adjust your calorie target based on real-world outcomes rather than the formula alone.