What is BMR (Basal Metabolic Rate)?
Basal Metabolic Rate (BMR) is the number of calories your body needs to carry out basic life-sustaining functions — breathing, pumping blood, keeping your temperature steady, repairing cells and powering your brain — while you are completely at rest. For most adults BMR makes up 60–70% of all the calories burned each day, so it is the biggest part of your metabolism.
Your BMR depends mainly on your body size, how much muscle you have, your age and your sex. Muscle burns more energy than fat, which is why men and people with more muscle usually have a higher BMR. BMR also falls gradually with age as muscle mass declines.
How the BMR calculator works (formulas)
1. Mifflin-St Jeor equation (recommended)
- Men: 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5
- Women: 10 × weight (kg) + 6.25 × height (cm) − 5 × age − 161
2. Revised Harris-Benedict equation
- Men: 88.362 + 13.397 × kg + 4.799 × cm − 5.677 × age
- Women: 447.593 + 9.247 × kg + 3.098 × cm − 4.330 × age
3. Katch-McArdle equation
370 + 21.6 × lean body mass (kg), where lean mass = weight × (1 − body fat % ÷ 100). Use our body fat calculator to estimate your body fat first.
Example: a 30-year-old woman, 165 cm, 60 kg: Mifflin-St Jeor BMR = 600 + 1,031 − 150 − 161 = 1,320 kcal; Harris-Benedict gives about 1,384 kcal.
BMR chart: low, normal and high values
Average BMR values for healthy adults are shown below. Your result depends heavily on your size.
| BMR level | Women | Men | What it usually means |
|---|---|---|---|
| Low | Under 1,200 kcal | Under 1,500 kcal | Small body size, older age or low muscle mass |
| Normal | 1,200 – 1,550 kcal | 1,500 – 1,900 kcal | Typical for average-sized adults |
| High | Over 1,550 kcal | Over 1,900 kcal | Taller, heavier or more muscular bodies |
Benefits of knowing your BMR
- It is your calorie “floor”: eating below your BMR for long periods can slow your metabolism and cause muscle loss.
- It powers every other calculation: your TDEE, calorie target and macros all start from BMR.
- Explains differences between people: why a friend can eat more than you without gaining weight.
- Motivation to build muscle: strength training is the most reliable way to raise your resting metabolism over time.
Health warnings
- BMR formulas are estimates for healthy adults. Results can differ by 10% or more from a lab test (indirect calorimetry).
- Hypothyroidism, some medicines (such as steroids or antidepressants), illness, fever and pregnancy change your metabolic rate.
- Very low-calorie diets reduce BMR and can cause fatigue, hair loss and gallstones. Do not eat below your BMR without medical supervision.
- Not suitable for children, teenagers or people with major illness or recent surgery.
How to support a healthy metabolism
Do strength training two to three times a week, eat enough protein (see the protein calculator), sleep 7–9 hours and avoid extreme diets. Iron, iodine and vitamin D deficiencies can leave you tired and sluggish — read our guides on iron deficiency and vitamin D.
Frequently asked questions
What is a normal BMR?
Most adult women have a BMR of about 1,200–1,550 kcal a day and most men about 1,500–1,900 kcal. Your normal depends on your height, weight, age and muscle mass.
Can I increase my BMR?
Yes, mainly by building muscle with regular strength training and eating enough protein. Avoiding crash diets and getting enough sleep also helps keep your metabolism working well.
Is it safe to eat less than my BMR?
Not for long. Regularly eating below your BMR can lead to muscle loss, nutrient deficiencies, fatigue and a slower metabolism. Base weight loss on your TDEE instead.
Which BMR formula is the most accurate?
For most healthy adults the Mifflin-St Jeor equation is the most accurate everyday formula. Katch-McArdle can be better if you know your body fat percentage accurately.
Why is my BMR lower than my friend’s?
Differences in height, weight, muscle mass, age and sex all change BMR. A taller or more muscular person burns more calories at rest.
Sources
- Mifflin MD, St Jeor ST, et al. Am J Clin Nutr 1990;51:241–247.
- Roza AM, Shizgal HM. The Harris Benedict equation reevaluated. Am J Clin Nutr 1984;40:168–182.
- Frankenfield D, et al. J Am Diet Assoc 2005;105:775–789.