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BMR Calculator Calculate your Basal Metabolic Rate using Mifflin-St Jeor and Harris-Benedict equations.

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BMR Calculator

Calculate your Basal Metabolic Rate using Mifflin-St Jeor and Harris-Benedict equations.

1

Select Units & Sex

Choose metric or imperial and your biological sex.

2

Enter Details

Input your age, weight, and height.

3

View Your BMR

See BMR from two different formulas and daily calorie needs at rest.

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What Is BMR Calculator?

The Basal Metabolic Rate (BMR) calculator estimates the number of calories your body burns at complete rest — just to maintain vital functions like breathing, circulation, and cell production. BMR accounts for approximately 60-75% of total daily calorie expenditure. This calculator uses two scientifically validated formulas: the Mifflin-St Jeor equation (considered most accurate for most people) and the Harris-Benedict equation (revised 1984). By knowing your BMR, you can better understand your body's energy needs and make informed decisions about nutrition and weight management. The calculator accounts for sex, age, weight, and height, and supports both metric and imperial measurement systems.

Why Use BMR Calculator?

  • Provides BMR from two scientifically validated formulas for comparison
  • Essential foundation for calculating total daily energy needs
  • Supports both metric and imperial measurement systems
  • Helps with weight management and nutrition planning

Common Use Cases

Weight Management

Understand your baseline calorie needs to plan weight loss or gain.

Nutrition Planning

Use BMR as the foundation for calculating daily calorie targets.

Fitness Programs

Combine with activity level to determine training nutrition needs.

Medical Assessment

Healthcare providers use BMR in metabolic evaluations.

Technical Guide

The Mifflin-St Jeor equation (1990) is: Males: BMR = 10W + 6.25H − 5A + 5; Females: BMR = 10W + 6.25H − 5A − 161, where W = weight in kg, H = height in cm, A = age in years. The Harris-Benedict equation (revised 1984) is: Males: BMR = 88.362 + 13.397W + 4.799H − 5.677A; Females: BMR = 447.593 + 9.247W + 3.098H − 4.330A. The Mifflin-St Jeor equation is generally considered more accurate (within 10% of measured values) and is recommended by the Academy of Nutrition and Dietetics. Both formulas account for the metabolic differences between sexes — males typically have higher BMR due to greater lean body mass.

Tips & Best Practices

  • 1
    Mifflin-St Jeor is generally more accurate than Harris-Benedict for most people
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    BMR decreases with age — roughly 1-2% per decade after age 20
  • 3
    Muscle mass increases BMR — strength training can boost your resting metabolism
  • 4
    BMR represents calories at complete rest — multiply by activity factor for total needs

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Frequently Asked Questions

Q What is the difference between BMR and RMR?
BMR is measured under strict resting conditions. RMR (Resting Metabolic Rate) is measured under less strict conditions and is typically 10-20% higher than BMR.
Q Which BMR formula is more accurate?
The Mifflin-St Jeor equation is considered more accurate for most people and is recommended by the Academy of Nutrition and Dietetics.
Q How many calories does BMR represent?
BMR typically accounts for 60-75% of your total daily energy expenditure, depending on your activity level.
Q Does muscle mass affect BMR?
Yes, muscle tissue burns more calories at rest than fat tissue. People with more muscle mass have higher BMRs.
Q Why does BMR decrease with age?
As we age, we tend to lose muscle mass and gain fat, which reduces BMR. Hormonal changes also play a role.

About This Tool

BMR Calculator is a free online tool by FreeToolkit.ai. All processing happens directly in your browser — your data never leaves your device. No registration or installation required.