What Formula Is Used to Calculate Daily Calorie Needs?

October 5, 2025 •

3 min read

The average person's basal metabolism accounts for 60% to 75% of their total daily energy expenditure. Understanding what formula is used to calculate daily calorie needs is the first step toward effective weight management and overall health.

Quick Summary

Several formulas are used to estimate daily calorie needs, starting with the Basal Metabolic Rate (BMR) and applying an activity factor. The Mifflin-St Jeor equation is considered one of the most accurate methods for this calculation.

Key Points

Mifflin-St Jeor Equation: This is the most accurate formula for estimating Basal Metabolic Rate (BMR) for the general population.
BMR to TDEE: Daily calorie needs are calculated by first finding your BMR and then multiplying that number by an activity multiplier to get your Total Daily Energy Expenditure (TDEE).
Activity Multiplier: The activity multiplier ranges from 1.2 for sedentary individuals to 1.9 for those who are extra active, adjusting the BMR for daily physical movement.
Harris-Benedict Equation: An older but still used method, this formula is known to sometimes overestimate calorie needs compared to the Mifflin-St Jeor equation.
TDEE for Weight Goals: To maintain weight, your calorie intake should match your TDEE. To lose weight, you need a calorie deficit, and for weight gain, a calorie surplus.
Other Factors: Metabolism is also affected by the thermic effect of food (TEF), body composition (muscle vs. fat), age, gender, and genetics.

The Core of Calorie Calculation: Basal Metabolic Rate (BMR)

To calculate your total daily calorie needs, you must first determine your Basal Metabolic Rate (BMR). BMR is the number of calories burned at rest for basic bodily functions like breathing and circulation. While precise BMR measurement requires lab equipment, predictive equations offer a good estimate.

The Most Accurate Method: The Mifflin-St Jeor Equation

The Mifflin-St Jeor equation is widely considered more accurate for the general population than the older Harris-Benedict equation. It uses weight, height, age, and gender to predict BMR. The specific formulas for men and women can be found here: {Link: NASM Bodyweight Tool https://www.nasm.org/resources/calorie-calculator}.

Other Equations: Harris-Benedict and Katch-McArdle

The Revised Harris-Benedict equation is an older formula that may overestimate calorie needs in overweight individuals. The Katch-McArdle formula considers lean body mass, which can be more accurate for very lean people but requires knowing body fat percentage.

Moving from BMR to TDEE: The Activity Multiplier

BMR only accounts for calories burned at rest. Total Daily Energy Expenditure (TDEE) includes BMR and calories burned through physical activity.

How to Apply the Activity Multiplier

Multiply your calculated BMR by an activity factor that reflects your average activity level to find your TDEE. A list of common activity multipliers for different levels (sedentary, lightly active, moderately active, very active, extra active) can be found here: {Link: NASM Bodyweight Tool https://www.nasm.org/resources/calorie-calculator}. Your TDEE estimates the calories needed daily to maintain your current weight.

Case Study: A Step-by-Step Calculation

Using the Mifflin-St Jeor equation and activity factors, one can calculate TDEE. For example, a 35-year-old male, 80 kg, 180 cm tall, exercising 3-5 days per week might calculate a BMR of 1755 kcal. Applying the moderately active multiplier (1.55) results in a TDEE of approximately 2720 kcal. Weight loss requires consuming fewer calories than this TDEE.

Comparison of Daily Calorie Need Formulas


Feature	Mifflin-St Jeor	Harris-Benedict	Katch-McArdle
Accuracy	Generally considered more accurate for the average population.	Older, tends to overestimate BMR, especially in the obese.	Most accurate for lean individuals, requires knowledge of body fat percentage.
Inputs Required	Weight (kg), Height (cm), Age (y), Gender	Weight (kg), Height (cm), Age (y), Gender	Lean Body Mass (LBM)
Calculation Steps	BMR + Activity Multiplier = TDEE	BMR + Activity Multiplier = TDEE	RDEE + Activity Multiplier = TDEE
Key Advantage	Improved accuracy based on updated research.	Long history of use, still common.	Better accounts for muscle mass, which burns more calories at rest.
Primary Limitation	Does not account for body composition; can be less accurate for very lean or very obese individuals.	Less accurate than Mifflin-St Jeor.	Requires body fat percentage, which can be difficult to measure accurately.

The Role of Thermic Effect of Food and Other Factors

TDEE also includes the thermic effect of food (TEF), the energy used for digestion, which is about 10% of total energy expenditure. Other factors influencing metabolic rate and calorie needs include gender, genetics, and health conditions.

Conclusion

The Mifflin-St Jeor equation is a reliable starting point for estimating daily calorie needs for most people. Calculating your BMR and applying an activity factor to determine TDEE provides a baseline for nutrition and exercise decisions related to weight management. This personalized approach is valuable, but for tailored advice, consult a healthcare provider or registered dietitian.

What formula is used to calculate daily calorie needs?

Frequently Asked Questions

BMR (Basal Metabolic Rate) is the number of calories your body needs to perform basic functions while at rest. TDEE (Total Daily Energy Expenditure) is your total daily calorie burn, which includes your BMR plus the energy from all your daily activities, including exercise and digestion.

The Mifflin-St Jeor equation is generally considered the most accurate formula for estimating BMR for the average person. The Katch-McArdle formula can be more accurate for very lean individuals, but it requires knowing your body fat percentage.

First, calculate your TDEE using a BMR formula and an activity multiplier. Then, to lose weight, you must consume fewer calories than your TDEE. A deficit of 500 calories per day often leads to a steady weight loss of about one pound per week.

Most reputable online calorie calculators use either the Mifflin-St Jeor or Harris-Benedict formulas as the basis for their calculations. They will ask for your age, gender, height, weight, and activity level to provide an estimated TDEE.

Your activity level is a crucial part of the calculation because it determines how many calories you burn through physical movement and exercise. A sedentary person burns far fewer calories than a very active person, even if they have the same BMR.

While factors like age and genetics are fixed, you can increase your BMR by building more lean muscle mass. Muscle tissue is more metabolically active than fat tissue, so increasing your muscle mass through resistance training will burn more calories at rest.

It's a good practice to recalculate your TDEE whenever you have a significant change in weight (5-10%) or a sustained change in your physical activity level. Your energy needs decrease as you lose weight.