BMR Calculator - Basal Metabolic Rate by Age, Gender, and Weight

You'll often see BMR and RMR (Resting Metabolic Rate) used interchangeably, and honestly, for most practical purposes they're close enough that the distinction doesn't matter much. But they aren't technically the same thing.

BMR is measured under very strict clinical conditions: you need to be in a thermally neutral environment, completely at rest, and in a fasted state after a full night of sleep. It's a true baseline, which makes it harder to measure precisely in the real world.

RMR is measured under slightly less rigid conditions. You still need to be at rest, but the requirements aren't as strict. As a result, RMR tends to run about 10 to 20 calories higher than BMR for the same person. Most online calculators, including this one, calculate something that's effectively closer to RMR in practice, even when they call it BMR. The formulas are the same; the label is just a bit loose by convention.

If BMR is your resting baseline, TDEE (Total Daily Energy Expenditure) is the full picture. TDEE accounts for everything you do on top of just existing: walking, working out, fidgeting, digesting food, even thinking.

You get from BMR to TDEE by multiplying your BMR by an activity multiplier, a number that reflects how active your daily life actually is. A sedentary person sitting at a desk all day has a TDEE that's roughly 1.2 times their BMR. Someone who trains hard five or six days a week might be closer to 1.7 or 1.8 times their BMR.

TDEE is the number that really drives weight management. Eat below your TDEE and you'll generally lose weight. Eat above it and you'll gain. BMR just gives you the foundation to calculate that number accurately.

Start by entering your age in years. BMR naturally declines as we get older, so age has a real impact on the result.

For weight, use your current weight rather than a goal weight. The formula needs to reflect where you are now, not where you want to be. You can enter it in pounds or kilograms depending on which unit you prefer.

For height, enter as accurately as you can. Even an inch or two makes a noticeable difference in the output. Use feet and inches or centimeters.

Finally, select your gender. The standard BMR formulas use biological sex as a variable because men and women have different average body compositions that affect resting calorie burn. If your situation is more nuanced, use whichever option gives you a result that feels most applicable and consider consulting a healthcare provider for a more personalized estimate.

Your BMR result is expressed in calories per day. It tells you the minimum your body needs just to sustain basic physiological functions if you were completely at rest for 24 hours.

A common mistake is treating BMR as a target calorie goal. It isn't. Eating only your BMR in calories would essentially be starvation-level intake for most people who move at all during the day. Your actual calorie needs are higher than this number once you account for any level of physical activity.

Think of your BMR as the starting point, not the finish line. It's the number you'll use to calculate your TDEE and, from there, set a realistic calorie target for your goals.

Multiply your BMR by the activity factor that best matches your typical week. The result is your estimated TDEE, the number of calories you need to maintain your current weight.

Be honest with yourself when picking a category. Most people overestimate how active they are, and that overestimation is one of the most common reasons calorie targets don't produce the expected results. When in doubt, go one level lower and adjust from there based on real-world results.

For most people, the Mifflin-St Jeor equation is the best starting point. Multiple studies have found it to be the most accurate predictor of resting metabolic rate across a wide range of body types. It's the formula most registered dietitians and nutrition software tools default to today.

The Harris-Benedict equation is the original, developed in 1919 and revised in 1984. It's still widely used and reasonably accurate, though research suggests it tends to run slightly high compared to measured values for many people.

If you know your body fat percentage with reasonable confidence, the Katch-McArdle formula can actually be more precise, because it bypasses the sex-based adjustment and works directly from lean mass. This makes it especially useful for very muscular individuals or those with a higher body fat percentage where the standard formulas may be less accurate.

The formulas for reference:

• Mifflin-St Jeor (Men): BMR = (10 × weight in kg) + (6.25 × height in cm) - (5 × age) + 5
• Mifflin-St Jeor (Women): BMR = (10 × weight in kg) + (6.25 × height in cm) - (5 × age) - 161
• Harris-Benedict (Men): BMR = 88.362 + (13.397 × weight in kg) + (4.799 × height in cm) - (5.677 × age)
• Harris-Benedict (Women): BMR = 447.593 + (9.247 × weight in kg) + (3.098 × height in cm) - (4.330 × age)
• Katch-McArdle: BMR = 370 + (21.6 × lean body mass in kg)

Men tend to have higher BMRs than women of the same age and size, largely because of differences in average muscle mass and hormonal profiles. The decline across age groups reflects the gradual loss of lean tissue and the natural slowdown in metabolic activity that comes with aging.

Women's average BMRs are lower than men's across every age group, reflecting differences in typical body size and lean mass rather than any inherent metabolic inefficiency. The same age-related decline applies, with the most noticeable drop often occurring around and after menopause due to hormonal shifts that affect body composition.

This one matters more than most people realize. Muscle tissue burns significantly more calories at rest than fat tissue. Estimates vary, but skeletal muscle is thought to burn roughly 6 calories per pound per day, while fat tissue burns closer to 2. That gap adds up fast when you're comparing two people of the same weight but different body compositions.

Someone who has spent years strength training and carries a lot of lean mass will have a meaningfully higher BMR than someone of the same weight who has a higher body fat percentage. This is one reason why resistance training is often recommended not just for performance but for long-term metabolic health. Building and maintaining muscle is one of the few ways to actively raise your BMR over time.

It's also why aggressive crash diets can backfire. Severe caloric restriction without adequate protein and resistance training tends to cause muscle loss alongside fat loss, which lowers BMR and makes continued weight loss progressively harder.

Metabolism does slow with age, but the story is a bit more nuanced than the common narrative suggests. The slowdown isn't dramatic from decade to decade. Research published in Science found that metabolism is relatively stable from roughly age 20 to 60, with a more noticeable decline beginning after 60.

A lot of what people attribute to a slowing metabolism in their 30s and 40s is actually a gradual loss of muscle mass, a process called sarcopenia, which begins as early as the late 20s if physical activity isn't sufficient to counteract it. Less muscle means a lower BMR, which means fewer calories burned at rest.

The practical takeaway: staying physically active, particularly with strength training, can slow this process considerably. Age-related metabolic decline is real, but it's not as inevitable or as steep as most people assume.

Men generally have higher BMRs than women, and the gap is real but often overstated in popular discussions. The difference comes down primarily to body composition. On average, men carry more lean muscle mass relative to their total body weight, and as covered above, muscle is more metabolically active than fat.

Hormones also play a role. Testosterone supports muscle protein synthesis and contributes to a higher proportion of lean tissue in men. Estrogen influences fat distribution and body composition in women in ways that generally result in a higher percentage of body fat at similar BMI levels.

After menopause, women often experience a shift in body composition toward higher fat and lower muscle mass, which can further reduce BMR if not addressed through diet and exercise. This is a significant reason why calorie needs can feel like they change noticeably in the years around menopause, even without major changes in activity level.