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Calculate your Basal Metabolic Rate using multiple proven formulas
Considered most accurate for general population
Original formula revised in 1984
Mean of all calculated formulas
| Formula | BMR Result | Best For | Accuracy |
|---|---|---|---|
| Mifflin-St Jeor | 0 cal/day | General population, overweight individuals | Highest (±10%) |
| Harris-Benedict | 0 cal/day | Average body composition | Good (±15%) |
| Katch-McArdle | N/A | Athletes, known body fat % | Highest with BF% (±5%) |
Basal Metabolic Rate (BMR) represents the minimum number of calories your body needs to maintain basic physiological functions while at complete rest. This includes breathing, circulation, cell production, nutrient processing, and temperature regulation. BMR typically accounts for 60-75% of your total daily calorie expenditure.
BMR and RMR are often used interchangeably, but there's a subtle difference. BMR is measured under very strict conditions (fasted, after 8 hours sleep, in a dark room), while RMR is measured under less restrictive conditions. RMR is typically 10-20% higher than BMR. Most calculators actually estimate RMR but call it BMR for simplicity.
For most people, the Mifflin-St Jeor equation provides the most accurate estimate. It was developed in 1990 and has been validated as more accurate than the older Harris-Benedict formula, especially for overweight individuals. If you know your body fat percentage accurately (from DEXA scan, hydrostatic weighing, etc.), the Katch-McArdle formula is most precise as it's based on lean body mass rather than total weight.
Your BMR is the foundation for calculating TDEE (Total Daily Energy Expenditure). Multiply your BMR by an activity factor to determine maintenance calories. Never eat significantly below your BMR for extended periods, as this can slow metabolism, cause muscle loss, and trigger adaptive thermogenesis. For healthy weight loss, maintain at least a 500-1000 calorie deficit from TDEE, not BMR.
During prolonged calorie restriction, your body adapts by lowering BMR beyond what's expected from weight loss alone. This adaptive thermogenesis can reduce BMR by 10-15%. Combat this with adequate protein intake, resistance training to preserve muscle, diet breaks, and reverse dieting phases. Regular refeeds and avoiding excessive cardio also help maintain metabolic rate.
While eating at BMR creates a deficit since your actual needs are higher, it's generally not recommended. Such an aggressive deficit can trigger metabolic adaptation, muscle loss, and hormonal disruptions. Instead, calculate your TDEE and create a moderate 500-750 calorie deficit from that number.
Different calculators use different formulas (Mifflin-St Jeor, Harris-Benedict, Katch-McArdle), which can produce variations of 100-300 calories. All formulas are estimates based on population averages. Your actual BMR may differ due to genetics, muscle mass, and metabolic efficiency. Use the calculated value as a starting point and adjust based on real results.
Build muscle through resistance training (muscle burns more calories at rest than fat). Stay adequately fed to avoid metabolic adaptation. Ensure sufficient protein intake. Get quality sleep (poor sleep reduces BMR). Stay hydrated and maintain healthy hormone levels. However, BMR increases from these factors are modest - focus primarily on increasing total activity for greater calorie burn.
No, meal frequency doesn't significantly affect BMR or total calorie burn. The thermic effect of food (TEF) is based on total calories and macronutrients consumed, not how many times you eat. Eating 6 small meals vs 3 larger meals burns essentially the same calories if total intake is equal. Choose a meal frequency that suits your lifestyle and hunger patterns.
BMR calculators are estimates accurate within 10-20% for most people. The Mifflin-St Jeor formula has about 10% error margin, while Katch-McArdle is more precise (5% error) if you have accurate body fat data. Individual variations in muscle mass, genetics, and metabolic efficiency mean your actual BMR may differ. Treat calculated BMR as a starting point, not an absolute.
Professional BMR testing via indirect calorimetry is more accurate but rarely necessary for general fitness goals. It costs $75-150 and provides precision within 5%. Consider testing if you've plateaued despite tracking carefully, have thyroid issues, or need exact numbers for competitive athletics. For most people, using calculated BMR and adjusting based on results over 2-3 weeks works perfectly well.
Yes, BMR decreases as you lose weight because you have less tissue requiring energy. Expect BMR to drop about 10-15 calories per pound lost. Additionally, adaptive thermogenesis can reduce BMR beyond weight loss alone. This is why calorie needs must be recalculated every 10-15 pounds lost. Preserve muscle through protein intake and strength training to minimize BMR reduction.
General guidelines suggest a minimum of 1500 calories for men and 1200 for women, though these are rough estimates. A better approach is to never eat below your BMR for extended periods. Very low calorie diets (under 1000 calories) should only be attempted under medical supervision. Insufficient calories lead to muscle loss, nutrient deficiencies, hormonal disruption, and metabolic damage.
This calculator provides estimates for educational purposes only and should not replace professional medical advice. BMR calculations are approximations based on population averages and may not reflect your individual metabolic rate. Consult with a healthcare provider, registered dietitian, or certified nutritionist before making significant dietary changes, especially if you have metabolic disorders, thyroid conditions, diabetes, or other health concerns. Professional metabolic testing via indirect calorimetry provides more accurate individual results.