Basal Metabolic Rate (BMR) is the number of calories your body needs to perform basic life-sustaining functions like breathing, circulation, and cell production while at complete rest. It accounts for 60-75% of your total daily energy expenditure. Knowing your BMR is crucial because it provides the baseline for determining your actual daily calorie needs based on your activity level, making it fundamental for effective weight management, nutrition planning, and understanding your body's energy requirements.

For more detailed information, you can refer to the Wikipedia page on Basal Metabolic Rate.

Our calculator using the Mifflin-St Jeor equation achieves 90-95% accuracy compared to indirect calorimetry (the gold standard lab test). The remaining variance comes from individual factors like genetics, hormone levels, and recent diet. For most people, this accuracy is sufficient for practical weight management. For clinical purposes or elite athletes, laboratory testing provides slightly higher precision but at significant cost and inconvenience.

Biological sex influences BMR because men typically have more lean muscle mass and less body fat than women of the same weight and height. Muscle tissue is metabolically more active than fat tissue, resulting in a higher BMR for men. The formulas account for these average differences. Our calculator respects all gender identities while using biological parameters necessary for metabolic accuracy. For transgender individuals undergoing hormone therapy, results may align more closely with their current hormonal profile after 6-12 months of consistent therapy.

Recalculate your BMR every 4-8 weeks during active weight management, or whenever you experience:

• Weight change of 5 kg or more
• Significant change in activity level (new job, injury recovery, training intensity change)
• Noticeable change in body composition (visible muscle gain or fat loss)
• Every 6 months for maintenance phases

BMR decreases with weight loss (smaller body requires less energy) and increases with muscle gain, so regular updates ensure your calorie targets remain accurate.

During pregnancy and breastfeeding, energy requirements increase significantly and standard BMR calculations don't apply. Pregnancy increases BMR by approximately 20% in the third trimester. Breastfeeding adds 300-500 calories daily to energy needs. We recommend consulting with a healthcare provider or registered dietitian for personalized guidance during these life stages. For general postpartum weight management, wait until breastfeeding is established (usually 6-8 weeks postpartum) before using BMR-based calorie targets, and never go below 1800 calories daily while breastfeeding.

These related terms describe different aspects of energy expenditure:

• BMR (Basal Metabolic Rate): Calories burned at complete rest in a thermoneutral environment after 8 hours of sleep and 12 hours of fasting. The strictest measurement.
• RMR (Resting Metabolic Rate): Similar to BMR but measured under less strict conditions. Typically 10-20% higher than BMR. What most "BMR" calculators actually estimate.
• TDEE (Total Daily Energy Expenditure): The total calories you burn in a day, including BMR, physical activity, exercise, and food digestion (thermic effect of food). Our calculator shows this as "Maintenance Calories."

For practical purposes, BMR and RMR are often used interchangeably, while TDEE is what matters for daily calorie intake decisions.

BMR typically declines by 1-2% per decade after age 20, primarily due to age-related muscle loss (sarcopenia) and hormonal changes. This is why people often gain weight despite unchanged eating habits. However, this decline isn't inevitable—resistance training can preserve or increase muscle mass, mitigating metabolic slowdown. Our calculator accounts for age in its formula, showing why calorie needs decrease over time. For older adults, we emphasize strength training and adequate protein intake (1.0-1.2g per kg of body weight) to maintain metabolic health.

If your calculated maintenance seems off, consider:

1. Verify inputs: Double-check height, weight, and especially activity level selection.
2. Activity adjustment: Most people overestimate activity. Try the next lower level.
3. Individual variation: Formulas predict averages. Your actual metabolism may vary by ±10% due to genetics, hormones, or body composition.
4. Track and adjust: Use the calculated number as a starting point, track your weight for 2-3 weeks, then adjust up or down by 100-200 calories based on results.
5. Consider body composition: If you have above-average muscle mass, try our Body Fat Calculator for a more personalized estimate.