What is the difference between BMR and RMR?

BMR (Basal Metabolic Rate) is measured under strict conditions: completely rested, fasted for 12 hours, in a thermoneutral environment. RMR (Resting Metabolic Rate) is measured under more relaxed conditions and is typically 10% higher. The Mifflin-St Jeor equation predicts BMR; in practice the two terms are often used interchangeably outside research settings.

Why does Mifflin-St Jeor use age?

BMR decreases with age, primarily because lean mass declines and basal metabolic activity in remaining tissue slows. The age coefficient (minus 5 kcal per year) captures this average decline. The effect is real but variable; regular resistance training preserves lean mass and slows it.

Can I use this BMR to calculate weight loss calories?

Not directly. BMR is your at-rest burn. To get your total daily burn (TDEE), multiply BMR by an activity factor between 1.2 (sedentary) and 1.9 (extra active). To lose weight, set your target intake 250 to 500 kcal per day below TDEE for a steady 0.5 to 1 lb per week. Our TDEE and calorie calculators do this math for you.

How accurate is the Mifflin-St Jeor equation?

For adults in the 18.5 to 35 BMI range, Mifflin-St Jeor predicts measured BMR within about 10% in 70% of subjects. For very lean individuals, very obese individuals, and athletes with high lean mass, it can underestimate by more than 10%; indirect calorimetry is the gold standard in those cases.

Your BMR is where every weight plan starts

Jillian Foglesong Stabile, MD

FAAFP, DABOM · Reviewed June 10, 2026 · Mifflin-St Jeor equation

Sex assigned at birth (the equation uses this)

Age

Height (feet)

Height (inches)

Weight

Screening estimate only, not a diagnosis. BMR is your at-rest energy floor and does not account for body composition, medications, or medical conditions, so a licensed physician determines eligibility for any treatment. Individual results vary.

Chapter 01 · The floor

What BMR actually is

Your Basal Metabolic Rate is the floor of your daily energy needs. It is the calories your body burns to keep you alive at rest: breathing, beating, repairing, signaling. For most adults, BMR accounts for 60% to 75% of total daily energy expenditure. The rest comes from physical activity and the thermic effect of food.¹

The Mifflin-St Jeor equation was published in 1990 and is now the recommended prediction equation for the general adult population. For men, BMR equals 10 times kilograms of body weight, plus 6.25 times height in centimeters, minus 5 times age in years, plus 5. For women, substitute minus 161 for that trailing constant. The constants encode the average sex-specific difference in lean mass.¹

Day type	Rough multiplier	What it represents
BMR (at rest)	The base	Energy burned at complete rest
Sedentary day	BMR times 1.2	Little or no exercise
Moderate day	BMR times 1.55	Some regular activity
Very active day	BMR times 1.725	Frequent hard training

Relative multipliers, not your personal figures.

Chapter 02 · The equation

Why Mifflin and not Harris-Benedict

The original prediction equation was Harris-Benedict (1919, revised in 1984). Harris-Benedict overestimates BMR for most modern adults by roughly 5%, primarily because body composition has shifted across the century since its derivation. Mifflin-St Jeor was derived from a more contemporary cohort and validated against indirect calorimetry. A 2005 systematic review recommended Mifflin-St Jeor as the most accurate predictor for the non-obese adult general population.²

The point: BMR is not the number you eat. It is the number you start from. Add activity to reach your daily target. Individual results vary.

Chapter 03 · The next step

What to do with this number

BMR is the number you start from. To estimate your total burn (TDEE), multiply BMR by an activity factor between 1.2 (sedentary) and 1.9 (extra active). To lose weight, subtract 250 to 500 kcal per day from your TDEE for a steady half to one pound per week. Any larger deficit is best done with a physician watching for muscle loss and adaptation. The physician, not this calculator, makes the clinical decision. Individual results vary.

Every medication on sipra is prescribed by a licensed physician, so your care always starts with a visit. Your sipra membership gives you ongoing access to those physician visits, so you can check in, adjust your plan, and ask questions whenever you need, without paying per visit. It is how we keep high-quality care convenient: one membership, physician access whenever you need it, and support at every step.

Sources

Mifflin MD et al. "A new predictive equation for resting energy expenditure in healthy individuals." American Journal of Clinical Nutrition. 1990;51(2):241-7. doi.org
Frankenfield D et al. "Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults." Journal of the American Dietetic Association. 2005;105(5):775-89. doi.org

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General education, not medical advice. Last reviewed June 10, 2026 by Jillian Foglesong Stabile, MD, FAAFP, DABOM. Prices snapshot Mifflin-St Jeor equation. Individual results vary.