What is the formula to calculate calories?

December 19, 2025 •

2 min read

Your Basal Metabolic Rate (BMR) accounts for 60% to 75% of your total daily energy expenditure, representing the calories your body burns at rest. Learning the core steps and understanding what is the formula to calculate calories is essential for anyone looking to manage their body weight effectively.

Quick Summary

This guide explains the step-by-step process for calculating daily calorie needs, detailing the popular Mifflin-St Jeor and Harris-Benedict equations. It covers the components of the formula, including Basal Metabolic Rate (BMR), Total Daily Energy Expenditure (TDEE), and crucial activity level multipliers. Key factors influencing metabolic rate are also discussed.

Key Points

Start with BMR: The formula begins with calculating your Basal Metabolic Rate (BMR), the calories your body burns at rest.
Choose the right equation: The Mifflin-St Jeor equation is often preferred for accuracy over the older Harris-Benedict formula.
Account for activity: Multiply your BMR by an activity factor to get your Total Daily Energy Expenditure (TDEE), which includes daily movement.
Recognize influencing factors: Your body composition, genetics, age, and health can all impact your actual metabolic rate, making formulas an estimate.
Understand macronutrient calories: Remember that carbohydrates and protein provide 4 calories per gram, while fats provide 9 calories per gram.
Set weight goals: Once you know your TDEE, you can create a calorie deficit to lose weight or a surplus to gain weight.

Understanding the Core Components: BMR and TDEE

To determine your daily calorie needs, you must first calculate your Basal Metabolic Rate (BMR), and then use that figure to estimate your Total Daily Energy Expenditure (TDEE). BMR represents the energy your body needs at complete rest to perform basic, life-sustaining functions like breathing, circulation, and cell production. Your TDEE is the total number of calories you burn in a day, which includes your BMR plus the energy expended during physical activity and food digestion.

Calculating BMR with Mifflin-St Jeor and Harris-Benedict Equations

The Mifflin-St Jeor equation, developed in the 1990s, is generally considered a more accurate method for estimating BMR for most individuals. The Harris-Benedict formula is an older method that was revised. While still used, it is often less accurate for modern populations. For the specific equations for men and women, please refer to {Link: NASM https://www.nasm.org/resources/calorie-calculator} or {Link: Steelfit USA https://steelfitusa.com/blogs/health-and-wellness/calculate-tdee}.

Step-by-Step Example Calculation

To calculate daily calorie needs, first determine BMR using one of the formulas. Then, multiply the BMR by an activity factor corresponding to your exercise level. For an example calculation demonstrating these steps, including determining the correct activity factor, please see {Link: NASM https://www.nasm.org/resources/calorie-calculator}. Adjusting calorie intake based on this TDEE is then needed for weight loss or gain. The activity level multipliers generally range from Sedentary (1.2) to Extra Active (1.9).

Factors Influencing Calorie Needs Beyond the Formula

Factors beyond these formulas also influence calorie requirements, such as body composition, hormones, genetics, age, and overall health. Macronutrients also contribute differently to calorie intake: carbohydrates and protein have 4 calories per gram, while fat has 9 calories per gram.

Comparison of Calorie Calculation Formulas


Feature	Mifflin-St Jeor Equation	Revised Harris-Benedict Equation
Development	Published in the 1990s	Published in 1919 and revised
Accuracy	More modern and generally considered more accurate for contemporary populations.	Less accurate for modern, less active populations due to age.
Key Variables	Weight, Height, Age, Sex	Weight, Height, Age, Sex
Application	Widely used in clinical settings and online calculators.	A traditional method, still used but increasingly replaced by newer equations.
Primary Use	Estimating BMR for calculating TDEE.	Estimating BMR for calculating TDEE.

Conclusion

Calculating calorie needs involves estimating your BMR with a formula like Mifflin-St Jeor, then multiplying by an activity factor to find your TDEE. This TDEE is a baseline for maintaining weight, adjustable for weight loss or gain. Remember, these are estimates; a healthcare provider can offer personalized guidance. For more on energy expenditure, consult resources like the NCBI.(https://www.ncbi.nlm.nih.gov/books/NBK499909/)

Frequently Asked Questions

BMR (Basal Metabolic Rate) is the number of calories your body needs to perform basic functions at rest. TDEE (Total Daily Energy Expenditure) is your BMR multiplied by an activity factor to account for all the calories you burn in a day, including exercise and other movements.

The Mifflin-St Jeor equation is generally considered a more accurate formula for calculating BMR than the older Harris-Benedict equation, especially for modern, diverse populations.

After calculating your TDEE, create a calorie deficit by consuming fewer calories than this number. A daily deficit of 500-750 calories is often recommended to achieve a healthy weight loss of about 0.5-1 kg per week.

Yes, muscle mass significantly impacts your metabolic rate. Individuals with a higher percentage of lean body mass burn more calories at rest than those with more body fat.

Your activity level is assigned a multiplier based on your weekly exercise habits, ranging from sedentary (little to no exercise) to extremely active (intense daily exercise). You multiply your BMR by this factor to determine your TDEE.

For those with a very physically demanding job, intense daily exercise, or multiple training sessions per day, an 'extra active' multiplier of 1.9 is used. Athletes or those with an extremely high level of activity may use an even higher factor.

Age is a key factor in calorie calculation formulas because BMR naturally decreases with age. This is largely due to a gradual reduction in lean body mass over time.