What is Basal Metabolic Rate (BMR)?

Your Basal Metabolic Rate (BMR) is the number of calories your body needs to accomplish its most basic, life-sustaining functions. Think of it as the energy you would burn if you were to stay in bed, at rest, for 24 hours. These essential functions include breathing, circulating blood, regulating body temperature, processing nutrients, and cellular growth and repair. Your BMR accounts for the largest portion of your daily calorie expenditure, typically making up about 60-75% of the total calories you burn in a day. It is the foundation upon which your entire dietary plan should be built.

BMR vs. RMR: What's the Difference?

You might also hear the term Resting Metabolic Rate (RMR). While BMR and RMR are often used interchangeably, there is a slight technical difference. BMR is measured under very restrictive conditions: in a dark, temperate room after a full night's sleep and a 12-hour fast. RMR is less restrictive and is simply the number of calories burned while at rest. RMR is typically slightly higher than BMR. For all practical purposes in diet planning, the difference is negligible, and BMR is the most commonly used term.

The Formulas Used to Calculate BMR

Our calculator allows you to choose between two of the most widely recognized formulas for estimating BMR.

1. The Mifflin-St Jeor Equation (1990)

Considered the modern standard, research has shown the Mifflin-St Jeor equation to be more accurate than the Harris-Benedict equation. It is the formula most often recommended by nutrition experts today.

For Men:

BMR = 10 × weight (kg) + 6.25 × height (cm) - 5 × age (y) + 5

For Women:

BMR = 10 × weight (kg) + 6.25 × height (cm) - 5 × age (y) - 161

2. The Revised Harris-Benedict Equation (1984)

This is a revised version of the original Harris-Benedict equation from 1919. For many years, it was the gold standard. While still widely used, it is considered slightly less accurate than the Mifflin-St Jeor formula for the general population.

For Men:

BMR = 88.362 + (13.397 × weight) + (4.799 × height) - (5.677 × age)

For Women:

BMR = 447.593 + (9.247 × weight) + (3.098 × height) - (4.330 × age)

From BMR to TDEE: Calculating Your Total Daily Calorie Needs

Your BMR is just your baseline. To determine your total daily calorie needs, you must account for your physical activity. This is your Total Daily Energy Expenditure (TDEE). It's calculated by multiplying your BMR by an activity factor.

• Sedentary: BMR × 1.2 (Little to no exercise, desk job)
• Lightly Active: BMR × 1.375 (Light exercise or sports 1-3 days a week)
• Moderately Active: BMR × 1.55 (Moderate exercise or sports 3-5 days a week)
• Very Active: BMR × 1.725 (Hard exercise or sports 6-7 days a week)
• Extra Active: BMR × 1.9 (Very hard exercise, physical job, or training twice a day)

Your TDEE for your specific activity level represents the number of calories you need to consume daily to maintain your current weight.

How to Use Your BMR and TDEE for Weight Management

• For Weight Loss: You need to create a calorie deficit by consuming fewer calories than your TDEE. A sustainable deficit is typically 300-500 calories per day.
• For Weight Gain (Muscle Building): You need to create a calorie surplus by consuming more calories than your TDEE, combined with resistance training. A surplus of 300-500 calories is a good starting point.
• For Weight Maintenance: Your daily calorie intake should be equal to your TDEE.

Frequently Asked Questions (FAQs)

1. Which formula should I use, Mifflin-St Jeor or Harris-Benedict?

For most people, the Mifflin-St Jeor formula is considered more accurate and is the recommended choice. We provide the Harris-Benedict option for comparison or for those who have been advised to use it specifically.

2. Why isn't body fat percentage used in the BMR calculation?

The Mifflin-St Jeor and Harris-Benedict formulas are based on total body weight. More advanced formulas, like the Katch-McArdle formula, do use lean body mass (which requires knowing your body fat percentage) and can be more accurate, especially for very athletic or very obese individuals. However, for the general population, the formulas provided here are highly effective and more accessible.

3. How often should I recalculate my BMR?

You should recalculate your BMR and TDEE whenever there is a significant change in your body weight (a loss or gain of 5-10 kg), or a major change in your activity level. Recalculating every few months during a weight loss or gain journey is a good practice.