BMR Calculator

The three equations

Mifflin-St Jeor (1990) — our headline result, and generally considered the most accurate predictive equation for healthy adults:

Men: 10 × kg + 6.25 × cm − 5 × age + 5
Women: 10 × kg + 6.25 × cm − 5 × age − 161

Harris-Benedict, revised by Roza & Shizgal (1984) — the classic 1919 equation updated with newer data. It tends to give slightly higher results than Mifflin-St Jeor:

Men: 88.362 + 13.397 × kg + 4.799 × cm − 5.677 × age
Women: 447.593 + 9.247 × kg + 3.098 × cm − 4.330 × age

Katch-McArdle — based on lean body mass rather than total weight, so it needs your body fat percentage. It can be more accurate for very lean or muscular people, provided the body fat estimate is good:

BMR = 370 + 21.6 × lean body mass (kg), where lean mass = weight × (1 − body fat % ÷ 100)

Don't know your body fat? Estimate it with our Body Fat Calculator, or leave the field blank.

BMR vs. RMR vs. TDEE

Strictly, BMR is measured after an overnight fast, fully rested, in a warm room. Resting metabolic rate (RMR) is measured under less strict conditions and is slightly higher. These equations actually predict resting energy expenditure, and the terms are used interchangeably. Your total daily energy expenditure (TDEE) adds activity on top — see the TDEE Calculator or the Calorie Calculator for daily targets.

What affects BMR?

Lean body mass is the biggest driver: muscle and organs burn more energy than fat. BMR also rises with height and body size, tends to fall with age, and is generally higher in men. Illness, fever, thyroid hormones, some medications, pregnancy and severe calorie restriction can all change it.

How BMR fits into daily calories

For most people, BMR accounts for about 60–70% of daily energy use, digesting food about 10%, and the rest comes from movement and exercise. To turn BMR into a full-day estimate, multiply it by an activity factor — from 1.2 for sedentary people to 1.9 for very active ones — or use the TDEE Calculator, which shows that breakdown for you.

Measured vs. predicted BMR

Clinics and some gyms can measure resting energy expenditure with indirect calorimetry, which analyzes the oxygen you breathe in and carbon dioxide you breathe out. It is more accurate for an individual than any equation and is sometimes used for people with obesity, older adults or patients in hospital, where predictive equations are less reliable.

Worked examples

Example 1: Woman, 25, 65 kg, 165 cm

Mifflin-St Jeor: 650 + 1,031.25 − 125 − 161 = 1,395 kcal/day. Harris-Benedict (revised) ≈ 1,452 kcal/day.

Example 2: Man, 30, 80 kg, 180 cm

Mifflin-St Jeor: 800 + 1,125 − 150 + 5 = 1,780 kcal/day. Harris-Benedict ≈ 1,854 kcal/day.

Example 3: Same man with 18% body fat

Lean mass = 80 × 0.82 = 65.6 kg. Katch-McArdle = 370 + 21.6 × 65.6 ≈ 1,787 kcal/day — close to Mifflin-St Jeor here.

Limitations

• All three equations predict averages; individuals can differ by 10% or more.
• Katch-McArdle is only as good as your body fat estimate.
• The equations were developed mostly in healthy adults and may not fit people with obesity, the elderly, or specific ethnic groups as well.

Who should not rely on this calculator

Not intended for children, pregnant or breastfeeding people, or anyone with a medical condition affecting metabolism (for example thyroid disease) or who is acutely ill. Clinical settings may use indirect calorimetry instead.