How to Calculate BMR: Formula, Meaning, and Examples

Searching how to calculate BMR means you want your basal metabolic rate — the number of calories your body uses at complete rest just to sustain essential functions. That includes breathing, circulation, cell repair, temperature regulation, and organ function. BMR is the foundation of all calorie calculations in nutrition and fitness.

What Is BMR?

BMR is the minimum number of calories your body needs to survive if you were lying completely still for 24 hours. It does not include any movement, exercise, or digestion. In practice, your actual daily calorie needs are higher because you move, eat, and live.

BMR typically represents 60–75% of total daily energy expenditure for most people with moderate activity levels. The rest comes from physical activity (20–30%) and the thermic effect of food (5–10%).

Common BMR Formulas

Mifflin-St Jeor Equation (Most Recommended)

This is the formula most frequently recommended by nutrition professionals and used by online calculators:

Men: BMR = 10W + 6.25H − 5A + 5

Women: BMR = 10W + 6.25H − 5A − 161

Where:

• W = weight in kilograms
• H = height in centimeters
• A = age in years

Harris-Benedict Equation (Revised 1984)

An older but still widely used formula:

Men: BMR = 88.362 + (13.397 × W) + (4.799 × H) − (5.677 × A)

Women: BMR = 447.593 + (9.247 × W) + (3.098 × H) − (4.330 × A)

Katch-McArdle Equation

This formula uses lean body mass instead of total body weight and is useful if you know your body fat percentage:

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

Lean body mass = Total weight × (1 − body fat percentage)

Mifflin-St Jeor Examples

Example 1: Adult Man

Age: 30 years Weight: 80 kg (176 lbs) Height: 180 cm (5 ft 11 in)

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

Example 2: Adult Woman

Age: 35 years Weight: 65 kg (143 lbs) Height: 165 cm (5 ft 5 in)

BMR = 10(65) + 6.25(165) − 5(35) − 161 BMR = 650 + 1,031.25 − 175 − 161 BMR = 1,345 calories/day

Example 3: Older Adult Man

Age: 60 years Weight: 90 kg (198 lbs) Height: 175 cm (5 ft 9 in)

BMR = 10(90) + 6.25(175) − 5(60) + 5 BMR = 900 + 1,093.75 − 300 + 5 BMR = 1,699 calories/day

Notice how BMR decreases with age due to the age term in the formula.

Converting Units for the Formula

If you know your stats in imperial units:

Pounds to kilograms: multiply by 0.453592

Feet and inches to centimeters: (feet × 30.48) + (inches × 2.54)

Examples:

• 160 lbs = 160 × 0.453592 = 72.6 kg
• 5 ft 6 in = (5 × 30.48) + (6 × 2.54) = 152.4 + 15.24 = 167.64 cm

BMR vs TDEE: The Difference

Term	What It Represents
BMR	Calories at complete rest
RMR	Similar to BMR, measured with less strict protocol
TDEE	Full daily calorie burn including activity

TDEE = BMR × Activity Multiplier

Activity Level	Multiplier	Example
Sedentary	1.2	Desk job, minimal movement
Lightly active	1.375	Light exercise 1–3 days/week
Moderately active	1.55	Exercise 3–5 days/week
Very active	1.725	Hard exercise 6–7 days/week
Extra active	1.9	Physical job + daily training

Using the man from Example 1 (BMR = 1,780):

If moderately active: TDEE = 1,780 × 1.55 = 2,759 calories/day

This is his maintenance calorie level — eating roughly this amount keeps his weight stable.

Why BMR Matters for Calorie Goals

Weight loss: You need to eat fewer calories than your TDEE, which is built on BMR. Going below BMR long-term is generally not recommended without medical supervision.

Weight gain: You eat above TDEE. Knowing BMR helps you understand the floor and ceiling of your calorie planning.

Maintenance: Eating near TDEE over time keeps weight stable.

Factors That Affect BMR

Body weight — heavier people have more tissue to maintain, so BMR is higher.

Muscle mass — muscle tissue is more metabolically active than fat. People with more muscle have higher BMR at the same body weight.

Age — BMR decreases roughly 1–2% per decade after age 20, primarily due to muscle loss.

Sex — men typically have higher BMR than women at the same height and weight due to greater average muscle mass and lower body fat percentage.

Hormones — thyroid hormones especially affect metabolic rate. Hypothyroidism lowers BMR; hyperthyroidism raises it.

Height — taller people have more surface area and slightly higher BMR.

Pregnancy and lactation — these significantly increase calorie needs beyond standard BMR.

How Accurate Are BMR Formulas?

No formula is perfectly accurate for every individual. Research shows Mifflin-St Jeor is among the most accurate population-wide formulas, with studies finding it within 10% of actual BMR for most people. However, your real metabolic rate could be 10–20% higher or lower than the formula predicts.

The gold standard for measuring BMR is indirect calorimetry (measuring oxygen consumption and CO2 production in a clinical setting), which is expensive and impractical for everyday use.

For practical purposes, use the formula result as a starting estimate, then adjust based on real weight trends over 2–4 weeks of consistent tracking.

The Bottom Line

To calculate BMR, use your age, sex, height, and weight in a formula such as Mifflin-St Jeor. Men use: BMR = 10W + 6.25H − 5A + 5. Women use: BMR = 10W + 6.25H − 5A − 161. BMR is the starting point for TDEE and daily calorie planning — not the goal by itself.

Use the TDEE Calculator to estimate both BMR and maintenance calories in one step, with adjustments for your activity level.

Informational note: BMR formulas are statistical estimates and vary from individual actual measurements. Medical conditions, medications, and body composition changes can affect real energy needs. Consult a healthcare professional or registered dietitian for personalized guidance.

How to Calculate: Step-by-Step Guide

1

Gather your stats

Use your age, sex, weight, and height.

2

Apply a BMR formula

A common formula is Mifflin-St Jeor.

3

Use BMR as a base

Multiply BMR by an activity factor to estimate TDEE.