What's the Formula for BMR? A Guide to Calculating Your Metabolic Rate

January 6, 2026 •

2 min read

According to the Cleveland Clinic, your basal metabolic rate (BMR) accounts for 60% to 70% of your total daily energy expenditure. Calculating your BMR is a foundational step in understanding your body's energy needs and creating a personalized strategy for weight management or fitness.

Quick Summary

This guide breaks down the Mifflin-St Jeor and Harris-Benedict formulas for calculating BMR, explains the key variables involved, and outlines how to use the results to estimate your total daily calorie needs.

Key Points

Most Accurate Formula: Use the Mifflin-St Jeor formula for a better BMR estimation compared to the Harris-Benedict equation.
Mifflin-St Jeor Equations: The formula structure is $BMR = (10 \times \text{weight in kg}) + (6.25 \times \text{height in cm}) - (5 \times \text{age in years}) + S$, with S varying for males and females. See {Link: NutriSwift.AI https://www.nutriswift.ai/post/the-harris-benedict-equation-understanding-your-basal-metabolic-rate} or {Link: NASM https://www.nasm.org/resources/calorie-calculator} for the exact values.
BMR vs. RMR: BMR and RMR are closely related; RMR is often used in practice due to easier measurement, closely approximating BMR.
Calculate TDEE: Multiply your BMR by an activity factor to estimate total daily calorie needs (TDEE). See {Link: NASM https://www.nasm.org/resources/calorie-calculator} for multiplier details.
Factors Affecting BMR: BMR is influenced by muscle mass, genetics, age, and thyroid hormone levels, among others. More details are on {Link: NutriSwift.AI https://www.nutriswift.ai/post/the-harris-benedict-equation-understanding-your-basal-metabolic-rate} or {Link: NASM https://www.nasm.org/resources/calorie-calculator}.
Application: Calculated BMR and TDEE are starting points for diet and exercise planning.

Understanding Basal Metabolic Rate (BMR)

Basal Metabolic Rate (BMR) is the minimum calories your body needs at rest for essential functions like breathing and circulation. It's a key metric for understanding your baseline energy requirements for weight management before considering physical activity.

While precise BMR measurement is done clinically, predictive equations offer accurate estimates. The Mifflin-St Jeor equation is highly regarded as the most accurate for modern populations, though the older Harris-Benedict formula is also used but considered less precise.

The Mifflin-St Jeor Formula

The Mifflin-St Jeor equation is a preferred method for calculating BMR. It uses your weight in kilograms, height in centimeters, and age in years. You can find the specific equations for males and females on {Link: NutriSwift.AI https://www.nutriswift.ai/post/the-harris-benedict-equation-understanding-your-basal-metabolic-rate} or {Link: NASM https://www.nasm.org/resources/calorie-calculator}. Ensure measurements are in the correct units; convert pounds to kilograms (divide by 2.20462) and inches to centimeters (multiply by 2.54).

The Harris-Benedict Equation

The Harris-Benedict equation is an older formula still in use, although the Mifflin-St Jeor is preferred for better accuracy. It also has gender-specific equations, which can be found along with the male and female formulas on {Link: NutriSwift.AI https://www.nutriswift.ai/post/the-harris-benedict-equation-understanding-your-basal-metabolic-rate} or {Link: NASM https://www.nasm.org/resources/calorie-calculator}.

Factors That Influence BMR

Several factors impact BMR beyond age, weight, and height, including muscle mass, body composition, genetics, age, environmental temperature, and thyroid hormones. A detailed list of factors can be found on {Link: NutriSwift.AI https://www.nutriswift.ai/post/the-harris-benedict-equation-understanding-your-basal-metabolic-rate} or {Link: NASM https://www.nasm.org/resources/calorie-calculator}.

BMR vs. RMR

BMR is measured under strict clinical conditions, while RMR (Resting Metabolic Rate) is measured under more common resting conditions. Though slightly different, RMR is often used in practice because it's easier to measure and closely approximates BMR. The Mifflin-St Jeor formula technically estimates RMR.

How to Calculate Total Daily Energy Expenditure (TDEE)

To estimate your daily calorie needs, calculate your TDEE by multiplying your BMR by an activity factor based on your lifestyle. You can find a table of activity level multipliers on {Link: NASM https://www.nasm.org/resources/calorie-calculator}.

Formula Comparison Table


Feature	Mifflin-St Jeor Formula	Harris-Benedict Formula
Development Year	1990	1919
Accuracy	Widely considered more accurate for modern populations.	Less accurate, especially for obese individuals.
Variables	Weight (kg), Height (cm), Age (years), Sex.	Weight (kg), Height (cm), Age (years), Sex.
Metric Version	Yes	Yes
Imperial Version	Yes (conversions needed)	Yes (original version)

Conclusion: Choosing the Right Formula

Knowing what's the formula for BMR is a valuable step for health goals. The Mifflin-St Jeor formula offers the most accurate BMR estimate for most people today. Remember that individual results can vary due to factors like genetics. Use your calculated BMR and TDEE as a starting point, adjusting your diet and activity as you monitor progress. For personalized advice, consult a healthcare provider or a registered dietitian.

Frequently Asked Questions

BMR (Basal Metabolic Rate) is the number of calories your body burns at complete rest, while TDEE (Total Daily Energy Expenditure) is your BMR adjusted for your daily physical activity level. TDEE gives you a more realistic estimate of your total daily calorie needs.

First, calculate your BMR using a formula like Mifflin-St Jeor, then determine your TDEE by multiplying your BMR by your activity level. To lose weight, you should consume fewer calories than your TDEE, creating a calorie deficit.

The Mifflin-St Jeor formula is generally considered more accurate and predictive for modern lifestyles and body compositions than the older Harris-Benedict equation, which can sometimes overestimate BMR.

Technically, an actual BMR requires clinical measurement under strict conditions, but predictive formulas like Mifflin-St Jeor provide a highly accurate and practical estimation for everyday use.

Building lean muscle mass is one of the most effective ways to increase your BMR, as muscle tissue burns more calories at rest than body fat. Other factors like genetics, age, and hormone levels also play a role.

Your BMR typically decreases with age, primarily due to a natural reduction in muscle mass. This is why older adults often require fewer calories to maintain their weight compared to younger adults.

No, BMR formulas are not accurate during pregnancy. Pregnancy significantly increases a woman's BMR due to increased body mass and the energy required for fetal growth. It's best to consult a healthcare provider for calorie needs during this time.