Basal Metabolic Rate (BMR)

Basal Metabolic Rate (BMR) is the energy your body uses at complete rest to maintain physiological functions: breathing, circulation, organ function, cellular maintenance. BMR is the largest single component of Total Daily Energy Expenditure (TDEE), typically 60-75% of daily calorie burn.

How calorie tracking apps estimate BMR

Most calorie tracking apps use one of two standard equations:

Mifflin-St Jeor (current standard, more accurate for modern populations):

• Men: BMR = (10 × weight kg) + (6.25 × height cm) − (5 × age years) + 5
• Women: BMR = (10 × weight kg) + (6.25 × height cm) − (5 × age years) − 161

Harris-Benedict (revised) (older, slightly less accurate):

• Men: BMR = 88.36 + (13.4 × weight kg) + (4.8 × height cm) − (5.7 × age years)
• Women: BMR = 447.6 + (9.2 × weight kg) + (3.1 × height cm) − (4.3 × age years)

Either equation produces an individual-specific BMR estimate accurate to within ±15-20% for most healthy adults. The actual measured BMR varies based on body composition (muscle mass burns more at rest than fat mass), thyroid function, and other individual factors that the equation does not capture.

BMR vs RMR

Resting Metabolic Rate (RMR) is a closely related concept measured under slightly less restrictive conditions than BMR (BMR requires fasting overnight and complete rest; RMR allows brief activity beforehand). For practical purposes in calorie tracking apps, BMR and RMR are used interchangeably.

BMR is not TDEE

A common misunderstanding: BMR is what you’d burn lying in bed all day. TDEE is what you actually burn including digestion, activity, and exercise — typically 1.2-1.7x your BMR depending on activity level. Eating only your BMR worth of calories will produce a substantial deficit and rapid weight loss; this is not sustainable for most people and is below the threshold for healthy long-term eating.

For setting calorie targets, work from TDEE, not BMR.