How to Calculate Your BMR (Basal Metabolic Rate) Step-by-Step

• Understand the difference between BMR and RMR.
• Use the Mifflin-St Jeor formula for the most accurate results.
• Learn how BMR connects to your total daily energy needs.

Understanding your basal metabolic rate (BMR) is one of the most helpful things you can do for your health. Whether you want to lose weight, gain muscle, or simply maintain your energy, knowing how many calories your body uses at rest gives you a clear foundation.

In this guide, we’ll walk you through how to calculate BMR step-by-step, explore different BMR formulas, and explain why it matters.

What Is BMR?

Basal Metabolic Rate (BMR) is the number of calories your body needs to function while at rest. This includes:

• Breathing
• Circulating blood
• Regulating temperature
• Cell growth and repair

Think of it as the bare minimum energy your body uses to stay alive—even if you did absolutely nothing all day.

BMR vs. Resting Metabolic Rate (RMR)

People often use BMR and Resting Metabolic Rate (RMR) interchangeably, but there’s a slight difference.

• BMR is measured under strict conditions (like after 8 hours of sleep and 12 hours of fasting).
• RMR is a bit more flexible and easier to measure, often slightly higher because it includes minimal movement.

For everyday use, the difference is small. Most online calculators and fitness apps use the terms similarly.

Why Your BMR Matters

Your BMR is the foundation of your Total Daily Energy Expenditure (TDEE)—which is the total number of calories you burn each day.

Knowing your BMR can help you:

• Set realistic weight loss or gain goals
• Avoid under- or overeating
• Build better meal plans
• Understand how your body works

What Affects Your BMR?

Several factors influence how high or low your BMR is:

• Age: BMR decreases with age.
• Gender: Men usually have higher BMRs due to more muscle mass.
• Weight and Height: Larger bodies burn more calories at rest.
• Body Composition: More muscle = higher BMR.
• Genetics: Some people naturally burn more calories.
• Hormones: Thyroid function plays a big role.

How to Calculate BMR: Step-by-Step

There are a few formulas used to calculate BMR. The most common and practical one today is the Mifflin-St Jeor Equation, which is considered more accurate than older models.

Step 1: Choose the Right BMR Formula

Here are the most popular formulas:

1. Mifflin-St Jeor Equation (Most Accurate)

• 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

2. Harris-Benedict Equation (Older, less accurate)

• Men:
  BMR = 66.5 + (13.75 × weight in kg) + (5.003 × height in cm) – (6.775 × age in years)
• Women:
  BMR = 655.1 + (9.563 × weight in kg) + (1.850 × height in cm) – (4.676 × age in years)

3. Katch-McArdle Formula (For those who know their body fat percentage)

• BMR = 370 + (21.6 × lean body mass in kg)

Step 2: Convert Measurements (If Needed)

Most formulas use metric units. Here’s how to convert if you’re using pounds and inches:

• Weight:
  pounds ÷ 2.2046 = kilograms
• Height:
  inches × 2.54 = centimeters

Step 3: Plug In Your Numbers

Let’s say you’re a 35-year-old woman, 5’6″ tall (167.6 cm), and weigh 150 lbs (68 kg). Using the Mifflin-St Jeor Equation:

BMR = 10 × 68 + 6.25 × 167.6 – 5 × 35 – 161
BMR = 680 + 1047.5 – 175 – 161 = 1391.5 calories/day

So, she burns about 1391 calories per day at rest.

Which BMR Formula Is Most Accurate?

Among the many options, Mifflin-St Jeor is currently considered the most accurate for the general population.

• It’s better than Harris-Benedict for modern lifestyles.
• It doesn’t require special tools (like Katch-McArdle does for body fat %).
• It aligns closely with clinical data.

If you have access to a body composition scan (like DEXA), Katch-McArdle is more personalized. But for most people, Mifflin-St Jeor is the best balance of ease and accuracy.

What to Do After You Calculate Your BMR

Once you know your BMR, the next step is to understand how many calories you burn in a full day—including all activity.

That’s your Total Daily Energy Expenditure (TDEE). It factors in how active you are.

Here’s a quick multiplier chart to estimate your TDEE:

Using our earlier example (BMR = 1391.5):

• If lightly active: 1391.5 × 1.375 = 1913 calories/day
• That’s her estimated TDEE

From here, you can adjust your calories:

• To lose weight: Eat 300–500 calories below your TDEE
• To gain weight: Eat 300–500 calories above your TDEE
• To maintain: Match your TDEE

Tools and Apps to Help You Calculate BMR

You can calculate BMR manually or use free online calculators and apps. Many use the Mifflin-St Jeor formula by default.

Popular tools:

• MyFitnessPal
• Cronometer
• MacroFactor
• TDEE Calculator.net

Just remember: these tools give estimates. Your real needs may vary slightly.

Tips for Using BMR Wisely

• Track trends, not single days. Energy needs can shift.
• Avoid extremes. Eating too far below your BMR can slow your metabolism.
• Recalculate if your weight, muscle mass, or activity changes significantly.
• Pair with mindful eating for best results.

Summary: Your BMR Is Your Starting Point

Knowing your Basal Metabolic Rate is like having a blueprint for your body’s energy needs. It’s simple to calculate, and the Mifflin-St Jeor equation makes it easy for most people to get an accurate number.

Whether you’re trying to lose fat, gain strength, or stay balanced, your BMR is the first number you need.

Want to Go Deeper?

Now that you understand how to calculate BMR, you’re ready to move on to the next step:

👉 Read Caloric Needs 101: How to Calculate Your Daily Energy Requirements