BMR Calculator

What is a BMR Calculator?

A BMR Calculator estimates your Basal Metabolic Rate — the number of calories your body burns simply to stay alive while completely at rest. Even when you are sleeping or lying still, your body is hard at work pumping blood, breathing, repairing cells, regulating temperature and powering your brain and organs. BMR represents the energy needed for all of these background processes, and it typically accounts for the largest share of the calories you burn each day.

Our BMR Calculator uses the Mifflin-St Jeor equation, which research has shown to be one of the most accurate predictive formulas for everyday use. After estimating your BMR, the tool multiplies it by an activity factor to give your Total Daily Energy Expenditure, or TDEE — a realistic estimate of how many calories you actually burn in a typical day once movement and exercise are included. Together these two numbers form the foundation of any sensible nutrition plan.

How to use the BMR Calculator

• Select your sex, since metabolic rate differs on average between men and women.
• Enter your age, height and weight in your preferred units.
• Choose the activity level that best matches your typical week.
• Read your BMR — the calories you burn at complete rest.
• Read your TDEE — your estimated daily maintenance calories once activity is included.

Key features

• Uses the modern, well-validated Mifflin-St Jeor equation.
• Accounts for age, sex, height and weight for a personalized result.
• Five activity levels from sedentary to very active.
• Shows both BMR and full daily maintenance calories (TDEE).
• Works in metric and imperial units.
• Free, private and runs entirely in your browser.

How the Mifflin-St Jeor equation works

The Mifflin-St Jeor equation was published in 1990 and has since become the formula of choice for dietitians and researchers because it predicts resting energy needs more accurately than older equations such as Harris-Benedict for the modern population. It combines your weight, height, age and sex into a single estimate, reflecting the fact that larger bodies, younger people and males tend to have higher resting metabolisms.

While the equation is remarkably reliable across most people, it remains an estimate based on population averages. Individual factors such as muscle mass, genetics, hormones and medical conditions can push your true BMR a little above or below the predicted value. The number it produces is best treated as an excellent starting point that you can fine-tune over time by observing how your weight responds to your actual eating habits.

From BMR to TDEE: why activity matters

Your BMR only describes the calories you burn at complete rest, but almost nobody spends the entire day lying down. Every step, gesture, workout and even the energy spent digesting food adds to your total. To capture this, the calculator multiplies your BMR by an activity factor ranging from sedentary to very active, producing your Total Daily Energy Expenditure.

Choosing the right activity level is the single biggest factor in getting a useful TDEE, and it is also where most people go wrong by overestimating how active they are. A desk job with occasional gym sessions is closer to lightly active than very active for many people. If your weight is not changing the way you expect after a few weeks, adjusting your activity level by one step is often the simplest fix.

Using your numbers for weight goals

Once you know your TDEE, managing your weight becomes a matter of arithmetic. Eating roughly at your TDEE keeps your weight stable, eating below it creates a deficit that leads to weight loss, and eating above it creates a surplus that supports weight or muscle gain. A common starting point for steady, sustainable fat loss is a deficit of around 300 to 500 calories per day, while a modest surplus of a similar size supports lean gains without excessive fat.

Because the calculator gives you both BMR and TDEE, you can set sensible boundaries for your plan. It is generally unwise to eat fewer calories than your BMR for any extended period, since that figure represents the minimum your body needs for its basic functions. Keeping your intake comfortably above your BMR while staying below your TDEE is the sweet spot for losing weight safely.

Tips for an accurate estimate

• Be honest about your activity level — most people overestimate it.
• Re-run the calculator after significant weight changes, as your BMR shifts with your weight.
• Use your TDEE as a starting point and adjust based on real-world results over two to three weeks.
• Pair the result with a calorie or macro calculator to plan your meals.
• Building muscle gradually raises your BMR, so strength training pays long-term dividends.

Why choose our BMR Calculator?

Our BMR Calculator uses the trusted Mifflin-St Jeor equation to give you accurate, personalized numbers in an instant, with no signup and nothing to install. It shows both your resting metabolic rate and your full daily maintenance calories, supports metric and imperial units, and keeps every calculation on your own device for complete privacy.

It is one of more than 200 free tools on ToopTools, and it fits naturally into your personalized My Workspace workspace. With My Workspace you can pin the BMR Calculator next to companion tools like the calorie and macro calculator and the BMI calculator, building a complete nutrition dashboard that stays ready whenever you sit down to plan your week.

Common use cases

People use a BMR calculator at the very start of a diet or fitness plan to discover how many calories their body actually needs, which prevents the common mistakes of eating far too little or far too much. It is the essential first step before setting a calorie target, designing a meal plan or choosing a macro split, because every later decision depends on knowing your maintenance level.

Coaches, personal trainers and nutrition-conscious individuals also return to the BMR calculator whenever circumstances change — after losing or gaining weight, becoming more active, or hitting a plateau. Recalculating keeps the plan aligned with the body's current needs, which is why the tool is just as useful for ongoing maintenance as it is for the first day of a new goal.

What is the difference between BMR and TDEE?

BMR is the number of calories your body burns at complete rest, just to keep its basic functions running. TDEE, or Total Daily Energy Expenditure, is your BMR multiplied by an activity factor to include movement, exercise and digestion. BMR is always the smaller number and represents your baseline, while TDEE reflects the calories you truly burn across a full, active day.

How accurate is the Mifflin-St Jeor equation?

The Mifflin-St Jeor equation is considered one of the most accurate predictive formulas available, and studies have found it estimates resting energy needs within about 10 percent for most people. It outperforms older equations for the modern population, though individual factors like muscle mass and genetics mean your true rate may differ slightly. Use the result as a strong starting point and refine it based on real results.

Should I eat below my BMR to lose weight?

Generally no. Your BMR represents the minimum calories your body needs for basic survival functions, so eating below it for long periods can be counterproductive and unsustainable. A safer approach is to create your calorie deficit relative to your TDEE — eating below maintenance but comfortably above your BMR — which supports steady fat loss while preserving energy and muscle.

Why does my BMR change over time?

BMR shifts as your body changes. It tends to fall as you lose weight or age, because a smaller or older body needs less energy, and it rises when you gain weight or build muscle. Muscle is more metabolically active than fat, which is why strength training can raise your BMR over time. It is worth recalculating after any significant change to keep your plan accurate.

Which activity level should I choose?

Pick the level that honestly reflects a typical week, not your most active day. Sedentary suits people with desk jobs and little exercise, lightly active fits one to three workouts a week, moderately active suits three to five, and very active fits intense daily training or physical jobs. Most people are less active than they think, so if in doubt, choose the lower option and adjust based on results.

Is my information stored anywhere?

No. The BMR Calculator performs every calculation directly in your browser, so your age, height, weight and other details never leave your device or get sent to a server. Nothing is saved or shared, which means you can use the tool freely and privately whenever you want to recheck your numbers.

How do I calculate my BMR?

Enter your age, sex, height, and weight, and the calculator uses the Mifflin-St Jeor equation to estimate your basal metabolic rate — the calories your body burns at rest. Add an activity level to also see your daily total energy expenditure (TDEE).

Does the BMR calculator work offline?

Yes. The calculation runs entirely in your browser, so once the page has loaded the tool works without an internet connection, and your details are never uploaded — they stay private on your own device.