What Is Basal Metabolic Rate (BMR)?

Your Basal Metabolic Rate (BMR) is the number of calories your body needs to maintain basic physiological functions — breathing, circulation, cell production, and temperature regulation — while at complete rest. It represents the minimum energy your body needs to survive and accounts for 60–75% of your total daily calorie expenditure.

How BMR Is Calculated

The most widely used formula is the Mifflin-St Jeor equation, developed in 1990 and validated in multiple studies:

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

For example, a 35-year-old woman who weighs 70 kg and is 165 cm tall has a BMR of approximately 1,469 calories per day.

BMR vs. TDEE

BMR is not the same as how many calories you should eat. Your Total Daily Energy Expenditure (TDEE) multiplies your BMR by an activity factor: sedentary (×1.2), lightly active (×1.375), moderately active (×1.55), very active (×1.725), or extremely active (×1.9). The woman in the example above, if moderately active, has a TDEE of approximately 2,277 calories — meaning she needs to eat that amount to maintain her current weight.

Using BMR for Weight Goals

To lose weight, eat below your TDEE (a 500 calorie/day deficit = ~1 lb/week loss). To gain weight or muscle, eat above your TDEE (a 300–500 calorie surplus). To maintain, eat at your TDEE. The key insight is that as you lose weight, your BMR decreases — which is why weight loss often plateaus and why recalculating regularly is important.

Factors That Affect BMR

Age (BMR decreases ~2% per decade after 20), muscle mass (muscle burns more calories than fat at rest), genetics, hormones (thyroid conditions significantly impact BMR), and body composition all influence your BMR. Building muscle through resistance training is one of the most effective long-term strategies for increasing BMR.

The Bottom Line

Knowing your BMR removes the guesswork from nutrition and weight management. It gives you a scientifically grounded starting point for setting calorie targets. Use our free BMR Calculator to find your number in seconds, then pair it with our Calorie Calculator for a complete nutrition plan.