BMR Calculator — Basal Metabolic Rate
Find your Basal Metabolic Rate — the calories your body burns at complete rest. Uses the validated Mifflin-St Jeor equation for accurate results.
Quick Answer
Your Basal Metabolic Rate (BMR) is the calories your body burns at complete rest — just to sustain breathing, circulation, and cell repair. It is calculated using the Mifflin-St Jeor equation. BMR is not a diet target — your TDEE (BMR × activity multiplier) is your actual daily calorie need.
What Is Basal Metabolic Rate?
Your Basal Metabolic Rate (BMR) is the number of calories your body burns to sustain essential life functions at complete rest — breathing, circulation, cell repair, organ function, and temperature regulation. If you lay in bed motionless for 24 hours, your body would still burn your BMR in calories just to keep you alive. BMR accounts for 60–75% of your total daily calorie expenditure, making it the foundation of all calorie planning.
Our calculator uses the Mifflin-St Jeor equation, validated in a 2005 meta-analysis in the Journal of the American Dietetic Association as the most accurate BMR formula for the general population. It outperforms the older Harris-Benedict equation (1919) and is the formula recommended by the Academy of Nutrition and Dietetics.
The Mifflin-St Jeor Formula
For men: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) + 5. For women: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) − 161. A 35-year-old man who weighs 80 kg and stands 178 cm tall has a BMR of approximately 1,835 kcal/day. At complete rest, his body burns 1,835 calories every single day.
What Affects Your BMR?
Four variables drive BMR: body weight (more mass = more energy to maintain), height (taller individuals have more metabolically active tissue), age (BMR declines with age, primarily due to muscle loss), and sex (men have higher BMR due to greater average muscle mass). The single most modifiable driver is muscle mass — each kilogram of muscle burns approximately 13 kcal/day at rest, compared to roughly 5 kcal/day for fat. This is why resistance training raises BMR over time.
BMR also declines during sustained caloric restriction, a phenomenon called metabolic adaptation. When you eat significantly below your needs, your body reduces BMR by 5–15% beyond what weight loss alone explains — your thyroid output drops, NEAT (non-exercise activity thermogenesis) decreases, and muscle protein synthesis slows. A moderate deficit of 500 kcal/day with high protein minimises this effect.
BMR vs TDEE: What You Actually Need
BMR is your absolute calorie floor — not a target for eating. Your Total Daily Energy Expenditure (TDEE) — BMR multiplied by your activity factor — is the number that matters for nutrition planning. For a moderately active person, TDEE is typically 1.4–1.6× their BMR. Eating at BMR long-term causes progressive muscle loss, nutrient deficiencies, and metabolic adaptation. Use the TDEE Calculator to convert your BMR into an actionable daily calorie target.
Never eat below your BMR
Eating at or below BMR for extended periods causes muscle loss and metabolic adaptation. Use BMR as a reference point, not a diet target. Your actual daily calorie needs are your TDEE.