BMR Calculator: Estimate Your Basal Metabolic Rate Accurately
Calculate your Basal Metabolic Rate (BMR) with the Mifflin-St Jeor formula. Find the minimum calories your body burns at rest to sustain vital organs.
Your Basal Metabolic Rate (BMR)
Calculated using the Mifflin-St Jeor equation — the most accurate for the general population.
📊 Formula Comparison
Most accurate for most adults (±10% margin)
Classic formula — tends to overestimate by ~5%
Enter body fat % above to unlock this formula
⚡ BMR → TDEE Preview
Your BMR is what you burn at complete rest. Multiply by your activity level to get your Total Daily Energy Expenditure (TDEE).
🔗 Continue with your results — data carries over automatically
Understanding Basal Metabolism: Cellular Energy & Organ Function
Your Basal Metabolic Rate (BMR) is the total number of calories your body requires to perform its most basic, life-sustaining functions while at complete rest. These functions include breathing, blood circulation, cellular respiration, nutrient processing, and temperature regulation. For the average adult, BMR accounts for roughly 60% to 75% of their Total Daily Energy Expenditure (TDEE).
Vital organs consume the vast majority of your resting calories: your liver burns ~27%, your brain consumes ~19%, skeletal muscle accounts for ~18%, your heart demands ~7%, and your kidneys use ~10%. Fat tissue, while metabolically active, burns less than 5% of resting energy.
Step-by-Step BMR Calculation Breakdown
How Mifflin-St Jeor calculates your baseline resting energy burn
Mifflin-St Jeor (Male)
Clinical formula for adult males:
Example (80kg, 180cm, 30yo):
800 + 1125 - 150 + 5 = 1,780 kcal
Mifflin-St Jeor (Female)
Clinical formula for adult females:
Example (65kg, 165cm, 30yo):
650 + 1031.25 - 150 - 161 = 1,370 kcal
Convert BMR to TDEE
BMR only measures sleep/bedrest burn. Never diet at BMR:
Find total daily maintenance calories using the companion TDEE tool.
Mifflin-St Jeor vs. Harris-Benedict: Historical Accuracy Comparison
- Mifflin-St Jeor Equation (1990): Validated against indirect calorimetry across thousands of subjects. The Academy of Nutrition and Dietetics recommends it as the gold-standard prediction equation for contemporary populations.
- Harris-Benedict Equation (1919, revised 1984): Historically famous but developed in an era with significantly different population body fat compositions. Modern metabolic cart studies demonstrate it systematically overestimates caloric requirements by 5% to 15%.
- Katch-McArdle Formula (1996): Uses Lean Body Mass (LBM) rather than total weight (`BMR = 370 + (21.6 * Lean Mass kg)`). For athletes or individuals with verified DEXA body fat scans, this provides superior physiological accuracy.
Where to Go Next: Recommended Companion Calculators
TDEE Calculator
Multiply your BMR by your daily activity level to find your true maintenance calories.
📉Calorie Deficit Calculator
Establish sustainable fat loss caloric targets while staying safely above your BMR floor.
🎖️Navy Body Fat Calculator
Determine your lean body mass to unlock the Katch-McArdle metabolic formula.
BMR vs. TDEE: A Critical Health Distinction
Never eat strictly at your BMR unless under direct medical supervision. Your BMR does not include the calories burned simply by getting out of bed, walking to the kitchen, or digesting food. To find your actual daily maintenance calories or deficit targets, you must multiply your BMR by an activity factor to find your TDEE.
Reviewed against peer-reviewed primary sources by the TDEEmacro Editorial Team · Last reviewed 2026-08-24
Formulas and clinical thresholds on this page are grounded in peer-reviewed primary literature and established physiological standards. Always consult a registered dietitian or physician before changing your dietary or exercise protocol.
- Validation of resting metabolic rate equations Frankenfield D, Roth-Yousey L, Compher C. Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review. J Am Diet Assoc. 2005;105(5):775-789.
- Katch-McArdle formula for lean body mass Katch FI, McArdle WD. Nutrition, Weight Control, and Exercise. 3rd ed. Lea & Febiger; 1988.
Frequently Asked Questions (Resting Calorie Burn, BMR vs TDEE & Health)
What is the difference between BMR and RMR?
BMR measures energy expenditure under strict laboratory fasting conditions, while Resting Metabolic Rate (RMR) is measured under less restrictive resting conditions and is typically 5-10% higher.
Should I ever eat fewer calories than my calculated BMR?
Eating below your BMR for extended periods is generally discouraged without medical supervision, as it can cause metabolic adaptation, micronutrient deficiencies, and hormonal disruption.
What is a good BMR for my age and gender?
There is no universally
What is the difference between BMR and TDEE?
Basal Metabolic Rate (BMR) is the strict number of calories your body requires for vital organ function while in a coma-like resting state. Total Daily Energy Expenditure (TDEE) is your BMR plus all the calories you burn from moving, working, digesting food, and exercising. You must base your diet targets on your TDEE, never just your BMR.
What happens if I eat fewer calories than my BMR to lose weight?
Eating below your BMR is dangerous and counterproductive. It forces your body into an adaptive starvation state where it aggressively suppresses thyroid hormone (T3) production, lowers your body temperature, and cannibalizes metabolically active skeletal muscle to survive. This permanently damages your metabolic rate and guarantees rapid fat regain (rebound weight).
Why does this BMR calculator use the Mifflin-St Jeor equation?
The Academy of Nutrition and Dietetics endorses the Mifflin-St Jeor formula (created in 1990) as the most accurate model for modern humans. Older formulas, like the 1919 Harris-Benedict equation, systematically overestimate resting metabolic rate by 5% to 15%, which can completely ruin a weight loss diet by setting your calories too high.
Can you naturally increase or change your BMR?
Yes, but the only sustainable way to increase your BMR is by building skeletal muscle mass through progressive resistance training. Muscle tissue is highly metabolically active; every pound of new muscle you build permanently increases the number of calories your body burns at rest 24/7.