How do you calculate resting energy requirement?

December 11, 2025 •

2 min read

Resting energy expenditure accounts for 60–75% of your total daily energy burn. Understanding this metabolic baseline is the first crucial step for anyone serious about managing their weight or optimizing their nutrition. This article explains how you calculate resting energy requirement (RER), also known as resting metabolic rate (RMR), with easy-to-follow methods.

Quick Summary

This guide provides step-by-step instructions for calculating resting energy requirements using both the Mifflin-St Jeor and Harris-Benedict equations. Learn the necessary variables and understand the difference between resting and basal metabolic rates to more accurately estimate your daily caloric needs for optimal health and wellness.

Key Points

Mifflin-St Jeor is the preferred formula: It is considered the most accurate predictive equation for estimating resting energy requirements (RER) in adults.
RER differs from BMR: Resting energy requirement (RER) accounts for minor daily activities and is slightly higher than the more strictly measured basal metabolic rate (BMR).
RER is the foundation for TDEE: Your RER calculation is the base number to which you apply an activity factor to find your Total Daily Energy Expenditure (TDEE).
Factors like age and body composition matter: RER is influenced by age, sex, weight, height, and body composition, with more muscle mass leading to a higher RER.
Calculations are estimates, not exact figures: Predictive formulas are powerful tools but provide estimates; actual caloric needs can vary by up to 50% between individuals.
Accuracy requires good data: To get the most accurate result from predictive equations, ensure you use your current, correct weight and height measurements.

Understanding Resting Energy Requirement (RER) vs. Basal Metabolic Rate (BMR)

Before diving into the calculations, it is essential to understand the difference between resting energy requirement (RER) and basal metabolic rate (BMR). BMR represents the minimum calories needed for vital functions in a completely rested state under strict lab conditions after fasting and sleep. RER, also known as Resting Metabolic Rate (RMR), is the energy expended in a rested but not completely inactive state, measured under less strict conditions than BMR.

The Most Accurate Equation: Mifflin-St Jeor

The Mifflin-St Jeor equation is widely regarded as the most accurate method for estimating RER, particularly for adults. It relies on your weight, height, age, and sex. The formulas for calculating RER using Mifflin-St Jeor are available on {Link: Fiveable https://fiveable.me/nutrition-assessment/unit-7/basal-metabolic-rate-bmr-resting-energy-expenditure-ree/study-guide/MozmGekLeVGx9jcD}.

Another Method: The Harris-Benedict Equation

The Harris-Benedict equation is an older formula from 1919 (revised in 1984) that is still used, though it is generally less accurate than Mifflin-St Jeor, especially for overweight individuals. Information on how to calculate RER using the Harris-Benedict method, including the formulas, can be found on {Link: Fiveable https://fiveable.me/nutrition-assessment/unit-7/basal-metabolic-rate-bmr-resting-energy-expenditure-ree/study-guide/MozmGekLeVGx9jcD}.

Comparison of RER Calculation Formulas

Predictive equations like Mifflin-St Jeor and Harris-Benedict use variables such as weight, height, age, and sex to estimate RER. While both methods are used, the Mifflin-St Jeor equation is generally considered more accurate, particularly for diverse adult populations, whereas Harris-Benedict can sometimes overestimate energy needs. For a detailed comparison table of RER calculation formulas, including their accuracy, variables, and best use cases, refer to {Link: Fiveable https://fiveable.me/nutrition-assessment/unit-7/basal-metabolic-rate-bmr-resting-energy-expenditure-ree/study-guide/MozmGekLeVGx9jcD}.

Converting RER to Total Daily Energy Expenditure (TDEE)

To determine your total daily caloric needs, multiply your RER by an activity factor that reflects your lifestyle. This gives you your Total Daily Energy Expenditure (TDEE). Activity factors range from sedentary (RER x 1.2) to extra active (RER x 1.9).

Factors Influencing RER

Several factors can cause individual RER to vary from predictive equation estimates:

Body Composition: More muscle mass increases RER.
Age: RER decreases with age due to muscle mass decline and metabolic changes.
Sex: Men generally have higher RER due to more lean muscle mass.
Genetics: Genetic factors can influence metabolic rate.
Hormonal Health: Thyroid conditions can significantly alter RER.

Conclusion

Calculating your resting energy requirement is a key step for effective nutrition and fitness planning. The Mifflin-St Jeor equation is the most recommended predictive method for estimating RER. By multiplying your RER by an appropriate activity factor, you can determine your total daily energy expenditure and set personalized goals. While these formulas provide valuable estimates, actual needs can vary, and clinical assessment is the most precise method. These predictive calculations offer a strong foundation for a data-driven approach to health. For more on the clinical context, you can visit {Link: the National Library of Medicine's resources https://www.ncbi.nlm.nih.gov/books/NBK278991/table/diet-treatment-obes.table12est/}.

Frequently Asked Questions

The primary difference is the conditions under which they are measured. BMR is the energy burned at complete rest, while RER includes the energy used for minimal, low-effort daily activities and is therefore slightly higher.

The Mifflin-St Jeor equation is generally considered the most reliable and accurate formula for estimating RER, especially for healthy adults and those who are obese.

You need your weight in kilograms, your height in centimeters, your age in years, and your sex to use the Mifflin-St Jeor or Harris-Benedict equations.

To find your Total Daily Energy Expenditure (TDEE), you multiply your RER by an activity factor that corresponds to your weekly exercise and physical activity levels.

The Harris-Benedict equation, being older, was developed with different population samples and can sometimes overestimate energy needs, especially in modern populations and obese individuals, making Mifflin-St Jeor a more modern and validated choice.

Yes, gaining muscle mass increases your RER because muscle tissue is more metabolically active than fat tissue, meaning it burns more calories at rest.

No, these equations are for humans. Veterinary medicine uses specific formulas for calculating resting energy requirements for pets like dogs and cats, such as $70 \times \text{(BWkg)}^{0.75}$.