BMR Calculator — Mifflin-St Jeor
This free BMR calculator (Mifflin-St Jeor) estimates your basal metabolic rate — the calories your body burns at complete rest — from your weight, height, age, and sex. It also shows a Harris-Benedict comparison and your estimated TDEE at every activity level. Results recalculate instantly in kg/cm or lb/ft+in.
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Enter your details to see your basal metabolic rate.
How to use this calculator
Pick your sex, then choose imperial (pounds, feet/inches) or metric (kilograms, centimeters) units — the calculator converts everything for you. Enter your weight, height, and age. Every number recalculates instantly as you change inputs — no need to press Calculate.
The headline result is your BMR (basal metabolic rate) from the Mifflin-St Jeor equation: the calories your body burns in a day doing absolutely nothing. Below it you will see a Harris-Benedict comparison so you can judge how much the two classic formulas differ for you, plus your estimated TDEE at five activity levels — BMR multiplied by a standard activity factor, which is where your real daily calorie needs live.
Remember what this page measures: your at-rest burn only. It is not a daily calorie target and not a weight-loss plan. For a safe daily intake target built on your total burn, use our calorie deficit calculator; for the full daily burn number, see the TDEE calculator.
How it works
The Mifflin-St Jeor equation (1990), with w = weight in kg, h = height in cm, a = age in years:
Men: BMR = 10 × w + 6.25 × h − 5 × a + 5
Women: BMR = 10 × w + 6.25 × h − 5 × a − 161
For example, a 30-year-old man who weighs 180 lb and is 5′10″ tall: 180 lb = 81.6 kg, 70 in = 177.8 cm. BMR = 10 × 81.6 + 6.25 × 177.8 − 5 × 30 + 5 = 816 + 1111.25 − 150 + 5 ≈ 1783 kcal/day.
The comparison uses the revised Harris-Benedict equations (w in kg, h in cm, a in years):
Men: BMR = 88.362 + 13.397 × w + 4.799 × h − 5.677 × a
Women: BMR = 447.593 + 9.247 × w + 3.098 × h − 4.330 × a
Imperial inputs are converted first (1 lb = 0.45359237 kg, 1 in = 2.54 cm), so both unit systems give the same result. TDEE estimates multiply the Mifflin-St Jeor BMR by standard activity factors: 1.2 (sedentary), 1.375 (lightly active), 1.55 (moderately active), 1.725 (very active), 1.9 (extremely active).
Important: these are population estimates, not medical advice. Both formulas were validated on average adults — they can over- or underestimate for very muscular, very lean, pregnant, elderly, or ill individuals. Actual metabolic rate varies with body composition, hormones, and medical conditions. Talk to a doctor or qualified clinician before making any diet or weight decisions based on these numbers.
Frequently asked questions
What is BMR?
BMR (basal metabolic rate) is the number of calories your body burns per day at complete rest — breathing, circulation, cell repair, and brain function — before you move, eat, or exercise. It usually makes up 60–70% of your total daily calorie burn, which is why it is the foundation of every calorie budget.
How is BMR different from TDEE?
BMR is your at-rest calorie floor; TDEE (total daily energy expenditure) adds everything on top — walking, working, exercise, and the calories used digesting food. TDEE is always higher than BMR. The Mifflin-St Jeor result on this page is multiplied by an activity factor to estimate TDEE, so this bmr calculator mifflin-st jeor result is the starting point, not your daily calorie target.
Which is more accurate: Mifflin-St Jeor or Harris-Benedict?
Mifflin-St Jeor (1990) is widely regarded as the more accurate of the two for most modern adults — validation studies show it predicts measured resting burn within about 10% for the majority of people. The original Harris-Benedict equation dates to 1919 and tends to overestimate; even the revised version usually lands a few percent higher. That is why this calculator shows Mifflin-St Jeor as the headline result and Harris-Benedict as a comparison.
Should I eat below my BMR to lose weight?
No. Eating at or below your BMR for long is considered unsafe — your body still needs that energy for basic functions, and chronic under-fueling risks muscle loss, hormonal disruption, and nutrient deficiencies. BMR is a floor to build on, not a calorie target. Use a calorie deficit calculator instead to find a safe daily intake based on your TDEE minus a modest deficit.
Is BMR the same as resting metabolic rate (RMR)?
They are closely related but not identical. BMR is measured under strict conditions — complete rest, fasting, in a dark, temperature-controlled room. RMR is measured at rest but under less strict conditions, so it usually comes out about 5–10% higher. For everyday calorie planning the difference is small, and formulas like Mifflin-St Jeor are commonly used for both.