Estimate Basal Metabolic Rate (BMR) and daily calorie needs with Mifflin-St Jeor formulas for weight maintenance, loss and gain.
The Basal Metabolic Rate (BMR) Calculator estimates your basal metabolic rate—the amount of energy expended while at rest in a neutrally temperate environment, and in a post-absorptive state (meaning that the digestive system is inactive, which requires about 12 hours of fasting).
Custom select height & weight measurement units
Basal Metabolic Rate is the minimum number of calories your body burns to sustain basic life functions while fully resting, in a thermally neutral environment with no food digestion (12-hour fast state). BMR accounts for 60-75% of total daily calorie expenditure for most sedentary adults. Vital functions powered by BMR include breathing, cell repair, brain function, blood circulation and organ maintenance.
This formula is clinically validated as the most accurate modern BMR estimation formula, replacing older Harris-Benedict equations.
Multiply your BMR by these standardized activity factors to calculate total daily calories required to maintain current body weight:
| Activity Tier | Multiplier | Full Description |
|---|---|---|
| Sedentary | 1.20 | Little or no intentional exercise, desk-bound daily lifestyle |
| Light Activity | 1.375 | Light exercise or sports 1–3 days weekly |
| Moderate Activity | 1.55 | Moderate intensity exercise or sports 4–5 days weekly |
| High Activity | 1.725 | Daily light exercise or intense training 3–4 times weekly |
| Very High Activity | 1.90 | Intense training 6–7 days every week |
| Extreme Activity | 2.30 | Daily very intense training + physically demanding full-time job |
The optional body fat percentage input adjusts BMR to account for lean mass. Muscle tissue consumes more resting calories than fat tissue, so users with high muscle mass can input body fat for a more precise BMR reading. If left blank, the standard Mifflin formula runs without lean mass correction.
To lose weight: Create a daily calorie deficit below your TDEE (500 calorie daily deficit equals ~1lb / 0.5kg fat loss per week). To gain muscle: Add a 250–500 calorie surplus above your maintenance TDEE while following resistance training. For weight maintenance, match your daily food intake to your calculated activity-matched TDEE value.
This calculator provides population-based estimations, not lab-grade indirect calorimetry measurements. Factors that alter real-world BMR include thyroid health, hormone disorders, pregnancy, medications, sleep deprivation and extreme muscle/obesity levels. For clinical metabolic analysis, consult a dietitian or endocrinologist for lab testing.