BMR Calculator

Published in 1990 and validated against indirect calorimetry in later studies, the Mifflin-St Jeor equation has largely replaced the older 1919 Harris-Benedict formula because it more closely matches measured resting energy expenditure in contemporary populations.

Men: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years) + 5. Women: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years) − 161. The +5/−161 constants adjust for typical differences in body composition between sexes at the same height and weight.

Take a 40-year-old man who is 180 cm tall and weighs 82 kg. His BMR = 10 × 82 + 6.25 × 180 − 5 × 40 + 5 = 820 + 1,125 − 200 + 5 = 1,750 calories per day.

That figure represents roughly what his body would burn lying in bed all day. His real daily needs (TDEE) will be noticeably higher once normal daily movement and any exercise are added — see our Calorie Calculator to apply an activity multiplier to this number.

Harris-Benedict (revised 1984) uses a similar structure but slightly different coefficients and tends to run a little higher than Mifflin-St Jeor for many adults. Katch-McArdle instead calculates BMR directly from lean body mass (BMR = 370 + 21.6 × lean mass in kg), which can be more accurate for people who know their body-fat percentage precisely, especially very lean or very muscular individuals.

For most people without access to accurate body-composition data, Mifflin-St Jeor remains the most practical and broadly validated starting point.

Muscle tissue burns more energy at rest than fat tissue, so building lean muscle through resistance training raises BMR over time, while losing muscle (from crash dieting, inactivity, or ageing) lowers it. BMR naturally declines with age, largely because muscle mass tends to shrink unless deliberately maintained through exercise, and it is also affected by genetics, thyroid function, and certain medications.

BMR typically accounts for 60–75% of total daily calorie burn in a sedentary adult, which is why it deserves attention even outside of active weight-loss planning. Understanding roughly how many calories your body needs simply to function helps you interpret why extremely low-calorie diets backfire, why muscle-building efforts pay off long after the gym session ends, and why two people who look similar on the outside can have noticeably different appetites and energy needs.

Some people use their BMR as a floor: a reminder not to eat consistently below that number even during an aggressive weight-loss phase, since doing so for extended periods risks nutrient deficiencies, hormonal disruption, and a metabolism that adapts downward to protect the body from what it perceives as starvation.

This tool is for general screening and education only. It is not a medical device and does not replace advice from a doctor, dietitian, or other qualified health professional — especially if you are pregnant, under 18, managing a chronic condition, or taking medication that affects weight or metabolism.