BMR Calculator — Basal Metabolic Rate

What is Basal Metabolic Rate (BMR)?

Your Basal Metabolic Rate is the number of calories your body needs just to survive at complete rest. Think of it as the energy cost of being alive — your heart beating, lungs breathing, brain thinking, and cells regenerating. Even if you stayed in bed all day doing absolutely nothing, your body would still burn this many calories.

For most people, BMR accounts for 60-75% of total daily calorie expenditure. This means the majority of the calories you burn each day go toward basic biological functions, not exercise. There is nothing physiologically magic about the BMR line itself - but the estimate carries around 150 calories of error, and very low intakes make lean-mass loss and nutrient shortfalls more likely, so we treat your estimated BMR as the sensible floor for any calorie target.

How the Mifflin-St Jeor equation works

Our calculator uses the Mifflin-St Jeor equation, published in 1990 and recommended by the Academy of Nutrition and Dietetics as the most accurate weight-based BMR formula for both normal-weight and obese adults. For men: BMR = (10 × weight in kg) + (6.25 × height in cm) - (5 × age) + 5. For women: BMR = (10 × weight in kg) + (6.25 × height in cm) - (5 × age) - 161. The gender difference exists mostly - though not entirely - because men typically carry more muscle mass, which burns more calories at rest; female sex is associated with a slightly lower resting rate even after accounting for body composition.

Mifflin-St Jeor replaced the older Harris-Benedict equation from 1919, which was built on a small early-20th-century sample and overestimates BMR in modern populations by around 5%. In head-to-head comparisons, Mifflin-St Jeor predicted measured metabolic rate within 10% for more people than any other weight-based formula.

Even the best equation is still an estimate. Individual prediction error runs around 150-160 calories per day, and roughly 1 in 3 people fall more than 10% from their measured value - which is why we show your BMR as a range, not a single number.

BMR vs TDEE — why you need both

BMR tells you the absolute minimum calories your body needs. But you don't lie in bed all day — you walk, work, exercise, and even digesting food burns calories. Your Total Daily Energy Expenditure (TDEE) adds these activity calories on top of your BMR.

For weight loss, you should eat below your TDEE but above your estimated BMR - a practical floor that keeps the deficit moderate and protects muscle and nutrient intake. A deficit sized at 0.5-1% of your body weight per week (typically 250-750 calories per day) is generally safe and sustainable.

Ready for the next step? Use our TDEE Calculator to find your total daily calorie needs, or go straight to the Macro Calculator to split those calories into protein, carbs, and fat.