If you have used a calorie calculator, you have probably seen the term BMR. It stands for basal metabolic rate, and it is the foundation of almost every estimate of how many calories you need. Understanding what it is, and what it is not, helps you set realistic expectations for weight loss.
What BMR means
Basal metabolic rate is the amount of energy your body uses to stay alive while completely at rest. Even when you are lying still, your body is busy: your heart pumps blood, your lungs breathe, your brain processes information, your kidneys filter blood, and your cells repair and replace themselves. All of that takes energy.
For most people who are not very active, BMR is the single biggest part of daily calorie burn. Activity and digestion are added on top of it to reach your total daily energy expenditure, or TDEE.
Strictly speaking, BMR is measured under strict laboratory conditions: after a night's sleep, fasted, at rest, in a comfortable temperature. A closely related term, resting metabolic rate (RMR), is measured under slightly looser conditions. In everyday use, people often treat the two as roughly interchangeable.
How BMR is estimated
Measuring BMR precisely requires specialized equipment that measures oxygen use and carbon dioxide production. Since most people do not have access to that, we rely on prediction equations built from studies of many people.
Our weight loss goal calculator uses the Mifflin-St Jeor equation, which is commonly recommended for estimating resting energy needs in adults:
- Men: (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) + 5
- Women: (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) − 161
For example, a 35-year-old woman who is 165 cm tall and weighs 80 kg would have an estimated BMR of about 10 × 80 + 6.25 × 165 − 5 × 35 − 161, which comes to roughly 1,495 calories per day.
Other equations exist, such as Harris-Benedict and Katch-McArdle (which uses lean body mass). They give somewhat different answers. None of them is exact for an individual, so the result is best thought of as a reasonable estimate.
What affects your BMR
Several factors influence how much energy your body uses at rest:
- Body size. Larger bodies generally need more energy to maintain, which is why BMR goes down a little as you lose weight.
- Body composition. Muscle tissue uses more energy than fat tissue at rest, so two people of the same weight can have different BMRs.
- Age. BMR tends to decline gradually with age, partly due to changes in muscle mass.
- Sex. On average, men have higher BMRs than women of the same size, largely due to differences in body composition.
- Genetics and hormones. Thyroid function and other hormonal factors can affect metabolism. If you suspect a thyroid problem, see a doctor.
- Health status. Illness, fever, and some medications can raise or lower energy use.
Common myths about metabolism
"My metabolism is broken." It is very rare for metabolism to be "broken." Differences between people exist, but in most cases slow progress is explained by underestimating food intake, overestimating activity, or normal water fluctuations.
"Eating small meals often boosts metabolism." Meal frequency has little effect on total daily energy use for most people. Choose the meal pattern that helps you control hunger and stick to your plan.
"Certain foods burn fat." Some foods and drinks, such as caffeine or spicy foods, may have small effects on energy use, but they are not a substitute for an overall calorie deficit.
Can you raise your BMR?
You cannot change your age, height, or genetics, but you can influence body composition. Strength training helps you build or maintain muscle, and eating enough protein supports that. Keeping muscle while losing fat can help limit the drop in BMR that comes with weight loss.
It is worth keeping expectations realistic. The increase in BMR from added muscle is modest. The bigger benefits of strength training are better strength, function, and body shape.
Why you should not eat at or below your BMR for long
Some people try to eat less than their BMR to speed up weight loss. For most, that is an aggressive deficit that makes it harder to get enough nutrients, may increase muscle loss, and often leads to fatigue and strong hunger. A moderate deficit below your TDEE, not your BMR, is usually a better approach. Our article on safe weekly weight-loss rates explains this in more detail.
How to use your BMR
- Use the calculator to estimate your BMR.
- Multiply by an activity factor to estimate your TDEE.
- Subtract a moderate deficit to get a daily calorie target.
- Track your progress for a few weeks and adjust.
BMR is a starting point, not a verdict. Real-world results matter more than any equation, and adjusting based on your own trend is the most reliable way to find what works for you.
The bottom line
Your BMR is the energy your body uses at rest, and it is the base of your daily calorie needs. Prediction equations like Mifflin-St Jeor offer a useful estimate. Combine that estimate with your activity level, a moderate deficit, and careful observation, and you have a solid foundation for reaching your goal. If you have a medical condition, talk with a healthcare professional about what is right for you.
This article is for general information only and is not medical advice. Talk with a qualified healthcare professional about your individual needs. Last updated November 1, 2026.