BMR Formula: How to Calculate Basal Metabolic Rate

The BMR formula is the starting point for every evidence-based diet plan. Your Basal Metabolic Rate represents the number of calories your body burns at complete rest just to keep you alive — powering your heartbeat, breathing, brain function, and cell repair. For most adults, BMR accounts for 60 to 75 percent of total daily energy expenditure, which makes getting this number right the single most important step in setting accurate calorie targets.

This guide walks you through the most widely used formulas for BMR, shows you exactly how to plug in your numbers, compares the results side by side, and helps you decide which basal metabolic rate equation fits your situation best.

The Mifflin-St Jeor Formula (Recommended)

Published in 1990 and validated in numerous clinical studies since then, the Mifflin-St Jeor formula is the equation recommended by the Academy of Nutrition and Dietetics as the most accurate for calculating BMR in the general population. A 2005 review by Frankenfield et al. confirmed it predicts resting metabolic rate within 10 percent for the largest share of individuals compared to any other non-calorimetry method.

Formula for men:

BMR = (10 x weight in kg) + (6.25 x height in cm) - (5 x age in years) + 5

Formula for women:

BMR = (10 x weight in kg) + (6.25 x height in cm) - (5 x age in years) - 161

How It Works Step by Step

Take a 30-year-old man who weighs 80 kg and stands 180 cm tall:

Multiply weight by 10: 80 x 10 = 800
Multiply height by 6.25: 180 x 6.25 = 1,125
Multiply age by 5: 30 x 5 = 150
Add the weight and height results: 800 + 1,125 = 1,925
Subtract the age result: 1,925 - 150 = 1,775
Add the male constant (+5): 1,775 + 5 = 1,780 kcal/day

For a 30-year-old woman with the same weight and height, the only difference is the final constant. Instead of adding 5, you subtract 161, giving 1,925 - 150 - 161 = 1,614 kcal/day.

Example BMR Values Using Mifflin-St Jeor

The table below shows calculated BMR for different body sizes to give you a realistic range of what to expect.

Men (age 30):

| Weight (kg) | Height (cm) | BMR (kcal/day) | |---|---|---| | 60 | 165 | 1,436 | | 70 | 170 | 1,568 | | 80 | 175 | 1,699 | | 80 | 180 | 1,730 | | 90 | 180 | 1,830 | | 100 | 185 | 1,962 |

Women (age 30):

| Weight (kg) | Height (cm) | BMR (kcal/day) | |---|---|---| | 50 | 155 | 1,147 | | 55 | 160 | 1,247 | | 60 | 165 | 1,270 | | 65 | 165 | 1,320 | | 70 | 170 | 1,401 | | 80 | 175 | 1,533 |

These numbers represent the calories your body needs at absolute rest. Your actual daily requirement will be higher once you factor in movement and activity.

The Harris-Benedict Formula (Original and Revised)

The original Harris-Benedict equation dates back to 1919, making it one of the oldest BMR formulas still in use. It was revised in 1984 by Roza and Shizgal to improve accuracy.

Revised Harris-Benedict for men:

BMR = (13.397 x weight in kg) + (4.799 x height in cm) - (5.677 x age in years) + 88.362

Revised Harris-Benedict for women:

BMR = (9.247 x weight in kg) + (3.098 x height in cm) - (4.330 x age in years) + 447.593

Worked Example

Using the same 30-year-old, 80 kg, 180 cm male:

13.397 x 80 = 1,071.76
4.799 x 180 = 863.82
5.677 x 30 = 170.31
1,071.76 + 863.82 - 170.31 + 88.362 = 1,853 kcal/day

Compare this to the Mifflin-St Jeor result of 1,780 kcal/day for the same person — a difference of 73 calories. This kind of gap is typical and is the main reason nutrition professionals prefer the newer formula.

Mifflin-St Jeor vs Harris-Benedict: Head-to-Head Comparison

Understanding the difference between these two formulas for metabolic rate helps you choose the right one. Here is a direct comparison across multiple profiles:

| Person | Age | Weight (kg) | Height (cm) | Mifflin-St Jeor | Harris-Benedict | Difference | |---|---|---|---|---|---|---| | Man A | 25 | 70 | 175 | 1,648 | 1,724 | +76 | | Man B | 40 | 90 | 180 | 1,780 | 1,858 | +78 | | Man C | 55 | 75 | 170 | 1,498 | 1,560 | +62 | | Woman A | 25 | 55 | 160 | 1,310 | 1,369 | +59 | | Woman B | 35 | 65 | 168 | 1,372 | 1,429 | +57 | | Woman C | 50 | 70 | 165 | 1,301 | 1,345 | +44 |

Key takeaways from this comparison:

Harris-Benedict consistently overestimates BMR by 40 to 80 kcal compared to Mifflin-St Jeor.
The overestimation is more pronounced in men and younger individuals.
For someone targeting fat loss, the Harris-Benedict equation could put you 500+ calories above your true deficit over a week — enough to stall weight loss entirely.
Mifflin-St Jeor has been validated against indirect calorimetry (the gold standard) and shown to be accurate within 10 percent for approximately 82 percent of individuals tested.

Bottom line: Use Mifflin-St Jeor unless you have a specific reason not to. It is newer, more widely validated, and less likely to overestimate your calorie needs.

From BMR to Daily Calories: The Activity Multiplier

The basal metabolic rate formula gives you your resting calorie burn, but you do not live at rest. To find your Total Daily Energy Expenditure (TDEE), multiply your BMR by an activity factor:

| Activity Level | Description | Multiplier | |---|---|---| | Sedentary | Desk job, little exercise | 1.2 | | Lightly active | Light exercise 1-3 days/week | 1.375 | | Moderately active | Moderate exercise 3-5 days/week | 1.55 | | Very active | Hard exercise 6-7 days/week | 1.725 | | Extremely active | Physical job + daily training | 1.9 |

Example: If your BMR is 1,780 kcal and you exercise moderately 4 days per week, your TDEE is approximately 1,780 x 1.55 = 2,759 kcal/day.

This TDEE number is what you actually use to plan your diet:

To lose weight: Eat 300-500 kcal below TDEE
To maintain weight: Eat at TDEE
To gain muscle: Eat 200-300 kcal above TDEE

Factors That Affect Your BMR

The formula for calculating BMR uses weight, height, age, and sex as inputs, but several other factors influence your actual metabolic rate:

1. Body composition. Muscle tissue burns roughly 6 kcal per pound per day at rest, while fat tissue burns about 2 kcal. Two people at the same weight can have significantly different BMRs depending on their lean mass.

2. Genetics. Studies on identical twins suggest that genetics account for 40 to 70 percent of the variation in BMR between individuals of similar size and age.

3. Hormones. Thyroid hormones (T3 and T4) directly regulate metabolic rate. Hypothyroidism can lower BMR by 15 to 40 percent, while hyperthyroidism can increase it substantially.

4. Dieting history. Prolonged caloric restriction causes metabolic adaptation, where BMR decreases beyond what weight loss alone would predict. This is sometimes called adaptive thermogenesis and can reduce BMR by 5 to 15 percent.

5. Temperature and climate. Cold exposure increases BMR as the body expends energy to maintain core temperature. This effect is modest in climate-controlled environments but measurable in extreme conditions.

When to Use Each Formula

General population: Use Mifflin-St Jeor. It is the standard recommendation and works well for most healthy adults.
Athletes with known body fat percentage: Consider the Katch-McArdle formula, which uses lean body mass instead of total weight: BMR = 370 + (21.6 x lean mass in kg).
Quick comparison or historical context: Harris-Benedict is fine as a reference point, but be aware it tends to overestimate.

No formula is perfect. All BMR equations are estimates, and individual variation means your true metabolic rate could be 10 to 15 percent higher or lower than the calculated value. The best approach is to use a formula as a starting point, track your actual intake and weight for 2 to 3 weeks, and then adjust based on real-world results.

Frequently Asked Questions

What is the most accurate formula for basal metabolic rate?

The Mifflin-St Jeor equation is considered the most accurate formula for basal metabolic rate in the general population. A systematic review by Frankenfield et al. found it predicted resting metabolic rate within 10 percent for more individuals than any competing equation. It requires only your weight, height, age, and sex — no body fat measurement needed.

How do I use the formula for calculating BMR if I only know my weight in pounds?

Divide your weight in pounds by 2.205 to convert to kilograms, and divide your height in inches by 0.3937 to convert to centimeters. Then plug those values into the Mifflin-St Jeor formula. For example, a 176 lb person weighs 79.8 kg, and someone 5 feet 11 inches (71 inches) tall is 180.3 cm.

What is the difference between the BMR formula and the basal metabolic rate equation in online calculators?

They are the same thing. Online calculators simply automate the basal metabolic rate equation so you do not have to do the math by hand. Most reputable calculators use the Mifflin-St Jeor formula, though some older tools still default to Harris-Benedict. Always check which equation a calculator uses before trusting its output.

Can the formula for metabolic rate change as I lose weight?

Yes. Every variable in the BMR formula — weight, and to a lesser extent body composition — changes as you lose weight. Recalculate your BMR every 5 to 10 kg of weight loss, or roughly every 4 to 6 weeks during an active diet phase. Failing to recalculate is a common reason people hit weight-loss plateaus.

Calculate Your BMR Now

Understanding the formula for BMR is valuable, but the fastest way to get your personal number is to use a calculator that does the math for you. Our BMR & TDEE Calculator uses the Mifflin-St Jeor equation and lets you instantly see both your basal metabolic rate and your total daily calorie needs based on your activity level. Enter your stats, get your numbers, and start building your nutrition plan on a solid foundation.