BMR Calculator

Frequently Asked Questions

• What is BMR?

  Basal Metabolic Rate — calories your body burns at complete rest (breathing, circulation, cell function). It accounts for 60-75% of total daily calorie burn for most people.

• BMR vs RMR — what's the difference?

  BMR is measured under strict conditions (overnight fast, complete rest, neutral environment). RMR (Resting Metabolic Rate) is measured under less strict conditions and is typically ~10% higher. The terms are often used interchangeably.

• Can I increase my BMR?

  Yes — by adding muscle mass through resistance training. Each kg of muscle burns ~13 kcal/day at rest. Diet, sleep and stress also influence BMR modestly.

• Why does BMR decrease with age?

  Loss of lean muscle mass and reduced cellular activity. Strength training and adequate protein intake significantly slow this decline.

• Is BMR different for men and women?

  Yes — men typically have higher BMR due to greater muscle mass and lower body fat. The Mifflin-St Jeor formula uses different constants for each sex.

• How accurate are BMR formulas?

  Within ±10% for most people. Indirect calorimetry (lab measurement) is more accurate but rarely available. The formulas are sufficient for everyday planning.

• Do I need to eat at least my BMR?

  For sustained periods, yes — eating below BMR risks muscle loss, hormonal disruption and rebound weight gain. Use a moderate deficit from TDEE, not BMR.

• Does my BMR change with diet?

  Yes — sustained calorie restriction causes "metabolic adaptation": BMR can drop 5-15% beyond what's expected from weight loss. This is why diet breaks help.

• Is the Katch-McArdle formula better?

  If you know your body fat % accurately, yes — because it accounts for lean mass directly. For most people without DEXA/calipers, Mifflin-St Jeor is more practical.

• Can illness affect BMR?

  Yes — fever increases BMR ~7% per 1°F (0.5°C). Hypothyroidism lowers it. Recovery from injury or surgery temporarily increases it.