Free BMR Calculator Online

What Is BMR? (Basal Metabolic Rate Explained)

Your Basal Metabolic Rate, or BMR, is the number of calories your body burns each day just to stay alive — before you take a single step, lift a single weight, or even digest a meal. It covers the energy cost of breathing, circulating blood, repairing cells, regulating body temperature, and keeping your brain and organs running while you're completely at rest. For most people, BMR makes up somewhere between 60 and 75 percent of total daily calorie burn, which is why it's the natural starting point for any accurate BMR calculator, diet plan, or fitness goal.

This free BMR calculator online uses your age, height, weight and gender to estimate this number in seconds, then layers your activity level on top to give you your full Total Daily Energy Expenditure (TDEE) — in other words, your real daily calorie needs calculator result — along with ready-made calorie targets for weight loss, fat loss, or muscle gain.

BMR Formulas Used in This Calculator

Different BMR calorie calculators use different equations, and this tool lets you pick between the three most respected options in the "Formula settings" panel.

Mifflin-St Jeor Equation (Default)

Published in 1990 and now the formula most dietitians and the Academy of Nutrition and Dietetics recommend as the most accurate BMR calculator for the general population:

Men: BMR = 10×weight(kg) + 6.25×height(cm) − 5×age + 5
Women: BMR = 10×weight(kg) + 6.25×height(cm) − 5×age − 161

Revised Harris-Benedict Equation

Originally developed in 1919 and revised in 1984, this is one of the oldest resting metabolism calculator formulas still in common use:

Men: BMR = 13.397×weight + 4.799×height − 5.677×age + 88.362
Women: BMR = 9.247×weight + 3.098×height − 4.330×age + 447.593

Katch-McArdle Formula

This basal calorie calculator formula factors in lean body mass rather than total weight, which makes it a strong choice if you know your body fat percentage — especially for muscular or very lean individuals where standard formulas can be less precise:

BMR = 370 + 21.6 × Lean Body Mass (kg)

BMR vs TDEE: What's the Difference?

BMR tells you how many calories you'd burn lying in bed all day. TDEE — Total Daily Energy Expenditure — adds everything else on top: walking, exercise, fidgeting, digestion, and daily life in general. This is why a resting calorie calculator alone isn't enough to plan your diet; you need to multiply your BMR by an activity multiplier to get a realistic daily energy expenditure calculator result, which is exactly what the activity level dropdown in this tool does automatically.

Using Your Results: Maintenance, Weight Loss & Muscle Gain

Once you have your TDEE, the goal table below your result shows practical calorie targets for the most common fitness goals:

• Maintenance calorie calculator result: eating at your TDEE keeps your weight roughly stable over time.
• BMR calculator for weight loss / fat loss: a deficit of 250–500 calories below TDEE supports gradual, sustainable fat loss without excessive muscle loss; a 1000-calorie deficit speeds this up but should be approached carefully and briefly.
• BMR calculator for muscle gain: a surplus of 250–500 calories above TDEE, paired with resistance training and sufficient protein, supports steady lean muscle growth while limiting excess fat gain.

As a rule of thumb, roughly 7,700 extra or missing calories corresponds to about one kilogram of body weight change, so a 500-calorie daily deficit works out to roughly 0.4–0.5 kg of fat loss per week for most people.

What Affects Your Basal Metabolic Rate?

• Muscle mass: Muscle tissue burns more calories at rest than fat tissue, so people with more lean mass tend to have a higher BMR.
• Age: BMR generally declines with age, largely due to a gradual, natural loss of muscle mass over the years.
• Gender: Men typically have a higher BMR than women of the same weight, mainly due to differences in average muscle mass and body composition.
• Genetics and hormones: Thyroid function and inherited metabolic traits can meaningfully shift BMR up or down between individuals of similar size.
• Body size: Larger bodies generally require more energy to maintain, which is why height and weight are core inputs to every accurate BMR calculator.

How to Increase Your Metabolic Rate Naturally

• Build muscle through resistance training. More lean mass raises your resting calorie burn over the long term.
• Don't undereat for extended periods. Chronic, severe calorie restriction can cause your body to adaptively lower its metabolic rate.
• Stay active throughout the day. Non-exercise movement (walking, standing, chores) adds up meaningfully to your total daily energy expenditure.
• Prioritise protein intake. Protein has a higher thermic effect than fats or carbs, meaning your body burns more calories digesting it.
• Sleep well. Poor sleep is linked to metabolic and hormonal disruption that can affect both appetite and energy expenditure.

Accuracy and Limitations

Even the most accurate BMR calculator is still an estimate. Formulas like Mifflin-St Jeor are built from population averages, so individual results can vary by a meaningful margin depending on genetics, muscle mass, hormonal health, and other factors that a simple calculator can't capture. Lab-based indirect calorimetry remains the gold standard for a precise measurement, but for everyday use, this online metabolic rate calculator gives a solid, actionable starting point that you can adjust over time based on your real-world results.

Final Thoughts

Use this BMR calculator with activity level as your starting point, then track your actual weight trend over 2–3 weeks at your chosen calorie target and adjust from there — your body's real-world response is always the final word over any formula. Bookmark this page and recalculate every time your weight, activity level, or goals change.