BMR Calculator
Calculate your Basal Metabolic Rate — the calories your body burns at complete rest to sustain basic physiological functions.
How to use this bmr calculator
- 1Enter your sex, age, current weight, and height.
- 2BMR is your calorie floor — eating below BMR for extended periods risks muscle loss and metabolic adaptation.
- 3Multiply your BMR by your activity factor (1.2–1.9) to estimate TDEE — your total daily calorie need.
- 4BMR declines with age — recalculate annually or when weight changes significantly.
How it's calculated
Mifflin-St Jeor: Men = 10×kg + 6.25×cm − 5×age + 5. Women = 10×kg + 6.25×cm − 5×age − 161.
About the BMR Calculator
Your Basal Metabolic Rate is the foundation of all calorie calculations. Understanding BMR changes how you think about food and weight management — it reveals that most of your daily calorie expenditure has nothing to do with exercise.
For a sedentary person, BMR accounts for approximately 60–75% of total daily energy expenditure. The thermic effect of food (digesting food) accounts for about 10%. Non-exercise activity thermogenesis (NEAT — fidgeting, posture, casual walking) accounts for 10–15%. Formal exercise, even for active people working out 5 days per week, typically accounts for only 10–20% of total daily expenditure. This is why exercise alone, without dietary management, produces slow weight loss: a 300-calorie workout is easily offset by a modest dietary indulgence.
The most clinically significant application of BMR is defining the minimum viable calorie intake. No sustainable weight loss plan should maintain daily calories below BMR for extended periods. For practical planning, maintaining intake at a moderate deficit below TDEE (not BMR) — typically 500 calories below TDEE for 1 lb/week loss — produces steady fat loss without metabolic and physiological consequences of severe restriction.
BMR measurement (rather than estimation) is available through metabolic testing — indirect calorimetry — which measures actual oxygen consumption at rest. This test is offered by some hospitals, sports medicine clinics, and specialized nutrition practitioners. For individuals whose weight is not responding as expected to dietary and exercise interventions, actual metabolic testing can reveal whether BMR is atypically high or low, providing information that meaningfully changes the intervention approach.
Frequently asked questions
What does BMR represent and what happens if I eat below it?
BMR represents the minimum calories required for basic physiological functions: breathing, circulation, organ function, cell repair, and temperature regulation. It is what you would burn lying completely still for 24 hours without eating. Eating consistently below BMR triggers metabolic adaptation: the body reduces BMR further, breaks down muscle for energy, disrupts hormones (reduced thyroid output, elevated cortisol), and causes extreme fatigue. Most registered dietitians recommend never going below 1,200 calories for women or 1,500 for men as sustained minimums.
How does BMR change with age?
BMR declines with age for two primary reasons: muscle mass reduction (sarcopenia) and changes in organ metabolism. After age 30, adults who do not resistance train lose approximately 3–8% of muscle mass per decade. Muscle is the most metabolically active tissue, burning approximately 6 calories per pound per day at rest. Organ metabolism also slows slightly with age independent of muscle changes. The result is most sedentary adults need 100–200 fewer calories per decade to maintain the same weight. Regular resistance training is the most effective way to slow BMR decline by preserving metabolically active muscle mass.
Why is BMR different for men and women?
The constants in the Mifflin-St Jeor formula (+5 for men, −161 for women) reflect genuine physiological differences in body composition. Men typically have a higher muscle-to-fat ratio at equivalent heights and weights — muscle burns more calories at rest than fat. Men also generally have larger hearts, lungs, and liver mass per unit of body weight. These differences mean a 160 lb man has a meaningfully higher BMR than a 160 lb woman of the same height and age. Individual variation within each sex is substantial and overlaps significantly.
Does eating small frequent meals boost metabolism?
No — meal frequency does not meaningfully affect BMR or TDEE in most people. The idea that 6 small meals per day stokes the metabolic fire has been repeatedly tested and repeatedly fails to show benefit over 3 meals with equal total calories. Total calorie and protein intake across the day matter far more than distribution. Some research suggests spreading protein evenly across meals benefits muscle protein synthesis, but this is about muscle adaptation, not metabolic rate.