BMR Formula

May 4, 2026

Your basal metabolic rate determines how many calories your body burns just to stay alive – beating your heart, breathing, maintaining body temperature, and processing food. This baseline figure is essential for anyone managing weight, building muscle, or optimizing nutrition. The BMR formula calculates this resting calorie expenditure based on your age, sex, height, and weight.

What Is the BMR Formula?

The BMR formula estimates the minimum energy (in calories) your body needs per day at complete rest. It’s different from your total daily calorie expenditure, which includes physical activity and the thermic effect of food. Understanding your BMR is the foundation for accurate nutrition planning.

Three main formulas are widely used:

Harris-Benedict (1919) – the oldest, now considered overestimated for modern populations
Mifflin-St Jeor (1990) – the gold standard for most people
Katch-McArdle (1977) – requires knowing your body fat percentage

Harris-Benedict BMR Formula

The Harris-Benedict equation was the first scientifically-derived BMR formula. Though dated, it’s still referenced for comparison.

For men: BMR = 88.362 + (13.397 × weight in kg) + (4.799 × height in cm) − (5.677 × age in years)

For women: BMR = 447.593 + (9.247 × weight in kg) + (3.098 × height in cm) − (4.330 × age in years)

Example (Harris-Benedict)

A 30-year-old man, 180 cm tall, weighing 80 kg:

BMR = 88.362 + (13.397 × 80) + (4.799 × 180) − (5.677 × 30) BMR = 88.362 + 1,071.76 + 863.82 − 170.31 BMR ≈ 1,854 calories/day

Mifflin-St Jeor BMR Formula

The Mifflin-St Jeor equation is recommended by most nutritionists and health professionals. It’s more accurate for modern populations than Harris-Benedict.

For men: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) + 5

For women: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) − 161

Example (Mifflin-St Jeor)

Same person – 30-year-old man, 180 cm, 80 kg:

BMR = (10 × 80) + (6.25 × 180) − (5 × 30) + 5 BMR = 800 + 1,125 − 150 + 5 BMR ≈ 1,780 calories/day

Notice the Mifflin-St Jeor result is about 74 calories lower than Harris-Benedict – a typical difference.

Katch-McArdle BMR Formula

The Katch-McArdle equation is the only formula that uses body composition rather than just height and weight. It’s the most accurate if you know your lean body mass (total weight minus fat mass).

BMR = 370 + (21.6 × lean body mass in kg)

Example (Katch-McArdle)

If the same man has 72 kg of lean body mass (80 kg total − 8 kg fat):

BMR = 370 + (21.6 × 72) BMR = 370 + 1,555.2 BMR ≈ 1,925 calories/day

This is higher than the other estimates because he has above-average muscle mass.

How to Calculate BMR: Step-by-Step

Step 1: Gather Your Data

Weight in kilograms (divide pounds by 2.205)
Height in centimeters (multiply inches by 2.54)
Age in years
Sex (male or female)
Body fat percentage (optional, for Katch-McArdle only)

Step 2: Choose a Formula

Mifflin-St Jeor – best for most people
Harris-Benedict – for comparison or if you prefer older data
Katch-McArdle – if you know your exact body composition

Step 3: Plug Numbers Into the Formula

Use the equation for your sex and method. Keep units consistent (metric or imperial; convert if needed).

Step 4: Calculate Total Daily Energy Expenditure (TDEE)

Multiply your BMR by your activity multiplier:

1.2 = sedentary (little or no exercise)
1.375 = lightly active (exercise 1–3 days/week)
1.55 = moderately active (exercise 3–5 days/week)
1.725 = very active (exercise 6–7 days/week)
1.9 = extremely active (intense daily exercise or physical job)

Example: BMR of 1,780 × 1.55 (moderate activity) = 2,459 calories/day

Interpreting Your BMR Result

Your BMR tells you the baseline. The actual number matters less than how you use it:

For weight loss: Eat 300–500 calories below your TDEE
For weight gain: Eat 300–500 calories above your TDEE
For maintenance: Eat roughly equal to your TDEE
Recheck every 3–6 months as BMR changes with age and body composition

A higher BMR means your body burns more calories at rest – typically because you have more muscle mass. A lower BMR may indicate less muscle, older age, or slower metabolism.

Factors That Affect Your BMR

Understanding what influences your basal metabolic rate helps you set realistic expectations:

Age – BMR decreases ~2% per decade after age 20
Sex – women typically have 5–10% lower BMR than men
Muscle mass – muscle tissue is metabolically active; more muscle = higher BMR
Body fat percentage – fat is less metabolically active than muscle
Genetics – some people naturally have faster or slower metabolism
Hormones – thyroid function, cortisol, estrogen, and testosterone all affect BMR
Nutrition – prolonged undereating suppresses BMR; adequate protein preserves muscle
Sleep – poor sleep correlates with lower BMR and slower weight loss
Temperature – cold climates increase BMR; your body burns more to stay warm

Why BMR Matters for Weight Management

Many people underestimate how many calories they need, thinking that extremely low intake will speed weight loss. In fact, eating far below your BMR triggers adaptive thermogenesis – your metabolism slows to conserve energy. This makes weight loss plateau and eventual weight regain more likely.

Conversely, calculating your true TDEE prevents the opposite mistake: eating slightly above maintenance and gaining weight unintentionally.

BMR vs. RMR: What’s the Difference?

Basal Metabolic Rate (BMR) and Resting Metabolic Rate (RMR) are closely related but not identical:

BMR – measured under strict lab conditions: fasted 12+ hours, complete rest for 30 minutes, climate-controlled room
RMR – measured in standard conditions, less stringent; typically 10–20% higher than BMR

For practical purposes, most calculators estimate “BMR” but actually calculate RMR. The difference is negligible for fitness and nutrition planning.

Practical Uses of the BMR Formula

Nutrition planning: Base your calorie targets on your actual needs, not guesses
Fitness tracking: Understand how much extra you burn during workouts
Metabolic health: Track changes in BMR over years to detect metabolic issues
Medical assessments: Doctors use BMR/RMR to diagnose thyroid disorders or metabolic syndrome
Performance optimization: Athletes use BMR to time nutrition around training

This article is informational. For personalized nutrition or fitness advice, consult a registered dietitian or certified health professional. Individual results vary based on genetics, medications, and medical conditions.

Frequently Asked Questions

What does BMR stand for?

BMR stands for Basal Metabolic Rate – the number of calories your body burns at rest to maintain vital functions like breathing, circulation, and cell production. It differs from daily calorie needs because it excludes activity and digestion.

Which BMR formula is most accurate?

The Mifflin-St Jeor equation is generally considered most accurate for modern populations, as it was developed using contemporary data. The Harris-Benedict formula tends to overestimate BMR by 5–15%, while Katch-McArdle is best if you know your exact body composition.

Can BMR change over time?

Yes. BMR decreases with age (roughly 2% per decade after age 20), increases with muscle mass, and drops during prolonged calorie restriction. Hormonal changes, metabolism disorders, and medications also affect your basal rate.

How do I use BMR to plan my diet?

Multiply your BMR by an activity factor (1.2–1.9) to get your Total Daily Energy Expenditure (TDEE). To lose weight, consume 300–500 calories below TDEE; to gain, consume above it. Adjust based on results every 2–3 weeks.

Do men and women have different BMR?

Yes. Women typically have 5–10% lower BMR than men of the same weight and age because they usually have less muscle mass and more body fat. The BMR formulas account for this via sex-specific coefficients.