BMR Calculator
Free BMR calculator. Estimate your basal metabolic rate using Mifflin-St Jeor or Katch-McArdle with optional body fat, metric or imperial input.
Before activity, workouts, and steps, your body already burns calories.
Estimate how many calories your body burns at rest each day.
Based on widely used BMR formulas.
What this number means
- BMR is not maintenance calories. It is only the fuel your body burns at complete rest. Eating at BMR leaves no room for movement and is almost always too low for a full day.
- No exercise or steps are included. Every time you stand up, walk, cook, or lift weights, the total goes up. Maintenance sits well above BMR for most people.
- Most total daily burn is movement plus digestion plus exercise. Together these push the real number 20 to 70 percent above BMR depending on how active you are.
- Use it as a baseline. Multiply by an activity factor to estimate maintenance, or pair it with a daily calorie or deficit goal to plan further.
What is BMR?
Basal metabolic rate is the number of calories your body burns in a day if you did absolutely nothing: lying still, fully rested, no digestion in progress, room held at a comfortable temperature. It is the quiet cost of simply being alive. Your heart keeps beating, your lungs keep breathing, your liver and kidneys keep filtering, your brain keeps thinking, and every cell in your body keeps running the basic chemistry of staying functional. All of that takes energy, and that energy is what BMR measures.
A useful way to picture it: if you spent a full 24 hours in bed doing nothing at all, BMR would be roughly what you spent. Most people burn between 1200 and 2000 kcal per day at rest, scaling up with body size and down with age. A large, lean, young male will sit near the top of that range. A small, older, less-muscular person will sit near the bottom. The rest of your day, the moving, eating, and training, gets added on top.
How to calculate BMR
Two formulas cover almost every real-world use.
Mifflin-St Jeor is the modern default. It has been validated across many populations and is the formula used by most dietitians and tracking apps. It only needs sex, age, weight, and height:
- Male: BMR = (10 x weight in kg) + (6.25 x height in cm) - (5 x age) + 5
- Female: BMR = (10 x weight in kg) + (6.25 x height in cm) - (5 x age) - 161
Katch-McArdle is used when you know your body fat percentage. Because it works from lean body mass rather than total weight, it usually gives a closer estimate for people with unusually high or low muscle mass. The formula is:
- Lean body mass (kg) = weight (kg) x (1 - body fat % / 100)
- BMR = 370 + 21.6 x lean body mass (kg)
If you enter a body fat percentage, the calculator at the top of this page uses Katch-McArdle as the primary number and still shows the Mifflin-St Jeor result as a comparison. If you leave body fat blank, Mifflin-St Jeor is the primary number on its own.
What is the difference between BMR and TDEE?
BMR is the floor. TDEE (total daily energy expenditure) is the ceiling. The gap between them is everything you do besides lying still.
TDEE is made up of four parts:
- BMR. Usually 60 to 75 percent of total daily burn for a typical adult.
- Thermic effect of food. The energy cost of digesting what you eat, about 8 to 12 percent of total calories and higher on high-protein days.
- NEAT (non-exercise activity thermogenesis). Standing, walking, fidgeting, chores, talking with your hands. Can range from 200 to 1000 kcal per day and is the most variable part.
- Exercise. Training you deliberately schedule. Typically the smallest slice unless you are a serious athlete.
A 1600 kcal BMR can turn into anything from a 2000 kcal TDEE for a very sedentary day to 3000+ kcal for someone who is on their feet all day and trains hard. For weight goals, TDEE is what you compare food intake against. BMR is the anchor underneath.
Why is BMR important?
Because it tells you roughly how much energy your body spends before you do anything. That single number becomes the input for every practical calorie plan you might build:
- Fat loss. Knowing your BMR stops you from accidentally setting a deficit that dips below what your body burns at rest. Eating below BMR for long stretches is tied to muscle loss, strong hunger, and stalled results.
- Maintenance. BMR multiplied by an activity factor gives you a starting maintenance target. It is the easiest way to translate a resting number into a usable daily calorie goal.
- Muscle gain. The mild surplus that supports muscle growth is measured relative to maintenance, and maintenance starts with BMR. Without it, the surplus is a guess.
Is BMR the same for everyone?
No. Four levers move it:
- Size. Bigger bodies burn more at rest. Lean mass matters most, which is why the Katch-McArdle formula works well when body fat is known.
- Sex. Men average higher BMRs than women of the same weight, mostly because men carry more lean mass on average. The formulas reflect that average difference.
- Age. BMR drops slowly across adulthood, about 1 to 2 percent per decade after 25, largely because lean mass declines if it is not maintained with training.
- Genetics and hormones. Thyroid function, sex hormones, and genetic variation can shift BMR by 5 to 10 percent in either direction relative to what a formula predicts.
Two adults with matching height, weight, age, and sex can have BMRs that differ by 150 to 300 kcal per day. The formulas predict a population average, not your exact number.
Is BMR accurate?
It is accurate as a starting estimate and imprecise as a personal measurement. Mifflin-St Jeor was built on indirect calorimetry data from thousands of people and predicts an individual's BMR within roughly 10 percent in most cases. Katch-McArdle narrows that gap a little when body composition is known. Neither formula can account for your thyroid, your sleep, the season, or how heavy your last training week was.
The practical move is to treat the calculator output as a hypothesis. Use it to plan a calorie target, track your weight for 2 to 4 weeks, and compare actual results against what the number predicted. If your real trend disagrees with the math by 100 to 200 kcal, adjust the math. That is how any population formula becomes useful for one specific body.
Can you increase your BMR?
A little. The biggest lever is building more lean mass. Muscle tissue costs roughly 13 kcal per kg per day at rest, compared to about 4 for fat tissue. Gaining 3 to 5 kg of muscle over a year of consistent training realistically adds 25 to 60 kcal per day to resting burn. That is small per day but steady, and it compounds when you stop gaining and stay there for years.
Other levers give smaller or shorter-lived effects. Very low calorie diets lower BMR through adaptive thermogenesis, so the opposite, eating at a reasonable calorie level with enough protein, keeps BMR from drifting down. Cold exposure and caffeine produce small temporary bumps but do not meaningfully change baseline burn. The honest answer is that BMR is mostly a function of how much living tissue you carry and how hard it has to work.
When to use BMR versus TDEE
A quick cheat sheet for deciding which number to plug into your plan:
| Goal | Use | Why |
|---|---|---|
| Understanding resting metabolism | BMR | That is literally what BMR measures. |
| Setting daily calorie intake | TDEE | BMR is the floor, TDEE reflects your actual day. |
| Planning a fat loss deficit | TDEE minus deficit | Aiming to stay above BMR keeps the cut safer. |
| Planning a muscle gain surplus | TDEE plus surplus | Growth depends on eating above what you burn. |
| Checking whether you are eating too little | BMR | If intake sits below BMR, that is a clear warning sign. |
Frequently asked questions
What is a BMR calculator?
A BMR calculator estimates the calories your body burns per day at complete rest, before any movement or exercise. It takes your sex, age, weight, and height, runs them through a validated formula like Mifflin-St Jeor or Katch-McArdle, and returns a resting calorie number you can use as the baseline for a daily nutrition plan.
How do I calculate my BMR?
The simplest method is the Mifflin-St Jeor formula. For men: 10 x weight in kg plus 6.25 x height in cm minus 5 x age plus 5. For women: the same formula minus 161 instead of plus 5. If you know your body fat percentage, Katch-McArdle works from lean body mass and is usually more accurate for very lean or very muscular bodies. The calculator above does both in one click.
What is the difference between BMR and TDEE?
BMR is the calories you burn at rest. TDEE, total daily energy expenditure, is the calories you burn across an entire normal day including movement, digestion, and exercise. TDEE is always higher than BMR for anyone who is not bedridden, usually by 20 to 70 percent depending on how active you are.
Is BMR the calories I burn at rest?
Yes. BMR measures the energy needed to keep your body running when it is doing nothing: heart pumping, lungs breathing, organs filtering, cells repairing. It does not include walking, fidgeting, digesting food, or exercising. Those show up as additional calories on top of BMR in the TDEE calculation.
Is my BMR the number of calories I should eat?
No. Eating at BMR leaves no room for activity and is almost always too low. For most people the daily eating target should be somewhere between BMR and TDEE, depending on whether you are maintaining, losing, or gaining. Using BMR as your calorie intake target for long periods is associated with muscle loss and metabolic downshift.
Does body fat percentage make BMR more accurate?
Usually, yes. Lean mass is the tissue that drives most of resting energy burn. When you provide a body fat percentage, the Katch-McArdle formula works from lean body mass and tends to land closer to reality for people who are more muscular or leaner than average. Mifflin-St Jeor works fine without body fat and is the common default.
Can I increase my BMR?
A little. The reliable lever is building more lean muscle through consistent resistance training, since muscle tissue burns more energy at rest than fat. Gaining a few kilograms of muscle over a year can add 25 to 60 kcal per day to resting burn. Other approaches like caffeine, cold exposure, and spicy food produce tiny or short-lived effects on BMR itself.
How accurate is this calculator?
This calculator uses two of the most widely validated formulas in nutrition science. Mifflin-St Jeor is the modern default across dietetics and tracking apps, replacing older equations like Harris-Benedict that tended to overestimate BMR in sedentary adults. Katch-McArdle steps in when body fat percentage is known and narrows the gap for lean and muscular populations where total weight alone can mislead.
The limits worth knowing. Any BMR formula is a population estimate, not a measurement of your specific metabolism. Real BMR is influenced by thyroid hormone levels, recent calorie intake, sleep, stress, temperature, and genetics, none of which a calculator can see. Two people with identical sex, age, weight, and height can differ by 150 to 300 kcal per day in their actual resting burn. Expect the result here to land within roughly 10 percent of your real number for most adults.
Treat the output as a useful starting point for planning, not a laboratory measurement. For the tightest accuracy, pair the estimate with 2 to 4 weeks of real-world tracking: steady intake, daily weigh-ins, 7-day rolling averages. Your scale is the final judge of whether any formula is close enough for your body. Anyone with a diagnosed metabolic condition should follow their clinician's guidance rather than a web calculator.
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