Calculate BMR: What It Is, Formulas, and How to Use It for Weight Loss or Muscle Gain

Knowing how to calculate your BMR (Basal Metabolic Rate) is essential for reaching fitness goals like losing weight, building muscle, or maintaining a healthy weight.

BMR represents the number of calories your body burns at complete rest to keep vital functions running, such as breathing, circulation, and temperature control.

This guide will teach you what BMR is, how to calculate it, which formulas to use, and how to apply it in practice.

What Is BMR?

Basal Metabolic Rate is the minimum number of calories your body needs to function even if you stay in bed all day without moving.

Why Calculating BMR Is Important

• Plan your nutrition: determine how many calories to eat for weight loss, maintenance, or muscle gain.
• Adjust training plans: calculate total daily energy expenditure (TDEE) for accurate goals.
• Avoid extreme diets: protect muscle mass and health.
• Boost results: control calorie deficits or surpluses precisely.

BMR vs. Total Daily Energy Expenditure (TDEE)

BMR: calories burned at rest.
TDEE: BMR + calories burned through daily activity and exercise.

Activity factor:
Sedentary: BMR x 1.2
Lightly active: BMR x 1.375
Moderately active: BMR x 1.55
Very active: BMR x 1.725
Extremely active: BMR x 1.9

BMR Formulas

Harris-Benedict (revised)
Men: BMR = 88.36 + (13.4 x weight kg) + (4.8 x height cm) – (5.7 x age)
Women: BMR = 447.6 + (9.2 x weight kg) + (3.1 x height cm) – (4.3 x age)

Mifflin-St Jeor (more accurate)
Men: BMR = (10 x weight kg) + (6.25 x height cm) – (5 x age) + 5
Women: BMR = (10 x weight kg) + (6.25 x height cm) – (5 x age) – 161

Example Calculation

Profile: woman, 30 years, 65 kg, 165 cm, moderate activity.
BMR = (10 x 65) + (6.25 x 165) – (5 x 30) – 161
BMR = 650 + 1,031.25 – 150 – 161 = 1,370 calories

TDEE:
1,370 x 1.55 = 2,123 calories/day

How to Use BMR for Weight Loss or Muscle Gain

Weight loss: 300–600 calorie deficit/day.
Muscle gain: 300–500 calorie surplus/day.
Maintenance: match your TDEE.

Online BMR Calculators

While online calculators are convenient, knowing the formulas helps validate results. In the Befit app, you can calculate your BMR instantly and get customized plans.

Common Mistakes

Incorrect weight/height data. Forgetting to apply the activity factor for TDEE. Making extreme calorie adjustments.

Tips to Boost Metabolism

Build muscle mass. Increase protein intake. Do strength training. Get enough sleep.

Download the Befit app!

BMR is the foundation of any nutrition and fitness plan. Calculating it allows you to set realistic, healthy goals for sustainable results. Download the Befit app to get your BMR and a personalized fitness plan.