Discover exactly how many calories your body burns at complete rest — then see how your activity level multiplies that number throughout the day.
Fill in your details and we will show your Basal Metabolic Rate — the calories your body burns each day at complete rest.
The basics
Basal Metabolic Rate (BMR) is the minimum number of calories your body needs to sustain its basic physiological functions at complete rest — breathing, circulating blood, regulating temperature, and keeping your organs running. It is the single largest component of your daily energy expenditure, typically accounting for 60–75% of the calories you burn each day.
This calculator uses the Mifflin-St Jeor equation — the most clinically validated formula for the general population. It uses your age, sex, height, and weight to estimate your resting calorie needs with greater accuracy than older equations such as Harris-Benedict.
Several factors influence how many calories you burn at rest. Body size is the biggest driver — larger bodies require more energy to maintain. Body composition matters too: muscle tissue is metabolically active and burns roughly 13 kcal/kg per day at rest, while fat tissue burns very little. Age plays a role as BMR naturally declines by 1–2% per decade, partly due to muscle loss. Sex affects BMR because males typically carry more lean mass. Thyroid hormones are one of the primary regulators of BMR, which is why thyroid disorders can cause dramatic changes in body weight.
Understanding your BMR gives you a foundation for any nutrition plan. Since your BMR represents your minimum calorie need, eating below it for extended periods risks muscle loss, nutrient deficiency, and metabolic adaptation. Conversely, knowing your BMR — and by extension your TDEE — helps you set a precise, moderate calorie deficit for fat loss or a controlled surplus for muscle gain. Most practitioners recommend a deficit of no more than 500–750 kcal/day below TDEE for sustainable fat loss.
BMR is the calories your body burns doing absolutely nothing — lying still all day. TDEE (Total Daily Energy Expenditure) builds on BMR by adding calories burned through physical activity, digesting food (the thermic effect of food, roughly 10% of intake), and all incidental movement (NEAT — fidgeting, walking, standing).
Yes — the most effective strategy is building lean muscle through consistent resistance training. Adequate protein intake (1.6–2.2 g/kg bodyweight) supports muscle retention during a deficit. Avoiding crash diets also helps, as very low calorie intake triggers metabolic adaptation — a protective suppression of BMR. Small, sustainable deficits paired with strength training preserve and even build metabolically active muscle over time.
FAQ
BMR stands for Basal Metabolic Rate. It is the number of calories your body needs at complete rest — lying still, fasting, and at a neutral temperature — just to sustain essential functions such as breathing, circulating blood, regulating body temperature, and keeping your organs working. It is the floor of your calorie expenditure, below which your body cannot function normally.
Not exactly. "Metabolism" is a broad term covering all chemical reactions in the body that convert food into energy. BMR is a specific, measurable component of metabolism — the resting portion. When people say someone has a "fast metabolism," they usually mean a higher BMR or a higher Total Daily Energy Expenditure (TDEE), which includes activity on top of BMR.
The Mifflin-St Jeor equation used in this calculator is the most validated formula for the general population, typically accurate within 10% for most people. It uses age, sex, height, and weight as inputs. Individual variation in body composition (muscle-to-fat ratio), hormones, and health status means real-world BMR can differ. For best accuracy, use your lean body mass via a formula such as Katch-McArdle — but that requires body-fat measurement.
Yes. On average, males have a higher BMR than females of the same height and weight. The main reason is that males carry proportionally more lean muscle mass, which burns more calories at rest than fat tissue. The Mifflin-St Jeor equation accounts for this with a sex-specific constant: +5 for males and −161 for females.
Yes. Skeletal muscle is metabolically active tissue — it burns calories at rest, unlike fat tissue which is relatively inert. Every kilogram of muscle you add raises your resting calorie burn by roughly 13 kcal/day. While the absolute number per kg is modest, building significant muscle through consistent resistance training can meaningfully raise your BMR over months and years.
It is generally not recommended. Eating below your BMR means providing your body with less energy than it needs just to stay alive, which can trigger muscle breakdown (as the body catabolises tissue for fuel), hormonal disruption, nutrient deficiencies, and a downward adaptive response in metabolism. A safer approach is to eat below your TDEE — your full daily expenditure including activity — to create a moderate deficit of 300–500 kcal/day.
The main factors are body size (taller and heavier people burn more), body composition (more muscle = higher BMR), age (BMR declines roughly 1–2% per decade after 30), sex (males typically higher), and genetics. Hormones — particularly thyroid hormones — play a large role; hypothyroidism can meaningfully suppress BMR while hyperthyroidism elevates it. Fever, extreme cold, and certain medications also temporarily alter BMR.
BMR is your resting energy requirement — what you burn doing absolutely nothing. TDEE (Total Daily Energy Expenditure) builds on BMR by adding the calories burned through physical activity, digesting food (the thermic effect of food, roughly 10% of intake), and all incidental movement (NEAT). For most people, TDEE is 20–90% higher than BMR depending on how active they are.
Yes, within limits. The most effective long-term strategy is building lean muscle through resistance training, since muscle tissue raises resting calorie burn. Adequate protein intake supports muscle retention. Staying active generally keeps your metabolism higher. Crash dieting or very low calorie intake can suppress BMR, so gradual, moderate deficits are better for long-term metabolic health.
Yes. BMR typically declines as you age, partly due to hormonal changes and partly because most people lose muscle mass (sarcopenia) as they get older — a process that begins gradually around age 30. Regular strength training can significantly slow this decline. The Mifflin-St Jeor equation directly accounts for age as a variable in its formula.
Keep exploring
BMR is the foundation of your calorie picture. These free Fitlydoo tools help you build the complete view.
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