Your basal metabolic rate is the energy your body spends just staying alive — breathing, circulating blood, keeping warm — measured at complete rest. The Mifflin-St Jeor equation, published in 1990 and validated against measured metabolic rates since, predicts it from four numbers: for men, 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5; for women the same, ending in − 161 instead of + 5. Studies consistently find it the most accurate of the common formulas for non-obese adults, which is why dietitians reach for it first. BMR is a foundation, not a target: nobody eats at BMR, because nobody lives at rest — multiply it by activity to get your TDEE in the Calorie Calculator.
A note on health results: every figure this tool gives is an estimate from a standard formula — it is not medical advice and it does not diagnose anything. Bodies vary, and formulas cannot see your health history. Use the result as a starting point, and consult a clinician or registered dietitian for personal health decisions.
How to use it
Pick your sex — the equation uses a different constant for men and women.
Enter age, weight and height — kg/cm or lbs/ft-in.
Read your BMR — per day, per week and per hour at rest.
Go one step further — the Calorie Calculator multiplies it by your activity level.
What you get
Mifflin-St Jeor — the best-validated BMR equation in common use.
Both unit systems — kg/cm or lbs/ft-in.
Day, week and hour — your resting burn at three scales.
Formula shown — your own numbers substituted into the equation, so you can check the maths.
Frequently asked questions
What is the Mifflin-St Jeor equation?
Men: BMR = 10 × weight in kg + 6.25 × height in cm − 5 × age in years + 5. Women: the same with − 161 at the end instead of + 5. It predicts resting calorie burn from body size and age, and research has found it more accurate than the older Harris-Benedict equation for most adults.
Should I eat exactly my BMR?
No. BMR assumes you lie still all day digesting nothing. Even a sedentary desk worker burns roughly 20% more than BMR just moving around and digesting food. Your real maintenance figure is your TDEE — BMR multiplied by an activity factor.
Why does BMR fall with age and weight loss?
The equation subtracts 5 kcal per year of age, reflecting the gradual loss of muscle mass as we get older. And a smaller body burns less: lose weight and your BMR drops too, which is one reason weight loss slows down over time.