Basal Metabolic Rate (BMR) Calculator

Basal Metabolic Rate (BMR) calculator to estimate calories your body burns at rest

Your Basal Metabolic Rate (BMR) is an estimate of how many calories your body uses in a day if you did nothing except basic life functions: breathing, circulation, temperature regulation, and cellular repair. It is not a weight loss plan and it is not your “allowed calories.” It is a baseline that helps you understand your energy needs before activity, training, and day to day movement are added.

This calculator is built for two types of users. If you want a fast answer, enter your sex, age, height, and weight, then calculate using the default method. If you want a more tailored estimate, you can switch the formula, and you can optionally select an activity level to estimate maintenance calories (often called TDEE, total daily energy expenditure). You are never forced to provide optional inputs, and the calculator will still give you a usable BMR estimate without them.

The output is designed to be actionable. First, you get your BMR in calories per day. Second, if you choose an activity level, you get an estimated maintenance calorie range for typical daily life at that activity factor. From there, you can interpret the numbers sensibly: if you consistently eat far below your estimated BMR, you are likely under-fueling. If you consistently eat above your estimated maintenance, you are likely in a surplus. Real outcomes still depend on adherence, measurement error, and day to day variability, but BMR is a useful anchor for planning.

Assumptions and how to use this calculator

• This is an estimate, not a clinical measurement. Lab tests (indirect calorimetry) can differ from formulas.
• The default method (Mifflin-St Jeor) is a widely used general-purpose estimate for adults.
• If you select Katch-McArdle, body fat percentage is required because it estimates BMR from lean body mass.
• Maintenance calories (TDEE) are estimated by multiplying BMR by an activity factor. This is a simplification.
• Results assume stable health conditions. Pregnancy, major illness, and some medications can change energy needs.

Common questions

What is the difference between BMR and maintenance calories (TDEE)?

BMR is calories burned at rest to keep you alive. Maintenance calories (TDEE) is an estimate of your total daily burn after including exercise, daily movement, and digestion. If you want a single daily calorie number to guide eating, TDEE is usually the better target. BMR is best used as a baseline reference.

Which BMR method should I use?

For most people, Mifflin-St Jeor is a solid default because it generally performs well in typical adult populations. Harris-Benedict is an older approach that some people prefer for consistency with older calculators. Katch-McArdle can be useful if you have a reasonably accurate body fat percentage, because it uses lean mass, but body fat estimates are often noisy, so the improved accuracy is not guaranteed.

What if I do not know my body fat percentage?

Do not guess aggressively. If you do not have a solid estimate from a reliable method, skip Katch-McArdle and use Mifflin-St Jeor or Harris-Benedict. A bad body fat input can make the result worse, not better.

Why does my BMR seem too high or too low?

Formulas are averages. Differences in muscle mass, genetics, sleep, stress, and measurement error (height, weight, and age entry) can push your real burn up or down. Also, people often confuse BMR with TDEE and expect the number to match how much they can eat without gaining weight. If you need a “real world” target, use the optional activity level to estimate maintenance, then adjust based on scale trend over 2 to 4 weeks.

Can I use this calculator for teenagers or older adults?

It can provide a rough estimate, but accuracy can be weaker at the extremes. For teenagers, growth and development can change energy needs. For older adults, body composition changes can affect energy expenditure. Use the number as a starting point and prioritize health guidance from a qualified professional if you have medical constraints or are managing a condition.

How can I make the estimate more accurate in practice?

Use accurate measurements, choose the correct unit system, and be honest about activity level. Then treat the result as a starting point and validate it with real data: track calories and body weight consistently, and adjust the target slowly based on a multi-week trend, not daily fluctuations.