BMR Calculator
Calculate Your Basal Metabolic Rate & Daily Calorie Needs
Basal Metabolic Rate Calculator
Calculate Your BMR & TDEE
Activity Level Multipliers
Understanding Basal Metabolic Rate (BMR)
Basal Metabolic Rate (BMR) is the number of calories your body requires to perform essential physiological functions at complete rest—breathing, circulation, cell production, nutrient processing, protein synthesis, and temperature regulation. BMR represents the minimum energy expenditure necessary to sustain life, accounting for 60-75% of total daily calorie burn for most people. It's measured under strict laboratory conditions: after 8 hours sleep, 12+ hours fasting, in a neutral temperature environment, with no physical or mental activity. BMR excludes calories burned through movement, exercise, digestion, or thermoregulation beyond baseline.
BMR is determined primarily by lean body mass (muscle tissue), age, gender, genetics, and hormonal status. Muscle tissue is metabolically expensive—burning approximately 6 calories per pound per day at rest versus only 2 calories per pound for fat tissue. This is why muscular individuals have higher BMRs than those with higher body fat percentages at identical weights. Men have 5-10% higher BMRs than women on average due to greater muscle mass and lower essential body fat. BMR peaks in childhood and adolescence during rapid growth, then declines approximately 1-2% per decade after age 30, primarily from age-related muscle loss (sarcopenia). Thyroid hormones (T3, T4) significantly regulate BMR—hypothyroidism lowers it, hyperthyroidism raises it.
BMR differs from Resting Metabolic Rate (RMR) and Total Daily Energy Expenditure (TDEE). RMR is less restrictive than BMR—measured without the strict fasting and rest conditions—and typically runs 5-10% higher than BMR, though the terms are often used interchangeably. TDEE represents total daily calorie burn including BMR/RMR plus all activity: intentional exercise, non-exercise activity thermogenesis (NEAT like fidgeting, standing, walking), and thermic effect of food (TEF—calories burned digesting food, approximately 10% of intake). For most people, TDEE = BMR × activity factor (1.2-1.9), though individual variability exists based on genetics, NEAT levels, and diet composition.
BMR Calculation Formulas
Mifflin-St Jeor Equation (Most Accurate for General Population)
The Mifflin-St Jeor equation, developed in 1990, is currently considered the most accurate BMR predictor for the general population, validated across diverse age groups and body compositions. It's recommended by the Academy of Nutrition and Dietetics as the standard for clinical practice.
For Men:
BMR = (10 × weight kg) + (6.25 × height cm) - (5 × age) + 5
For Women:
BMR = (10 × weight kg) + (6.25 × height cm) - (5 × age) - 161
Mifflin-St Jeor predicts BMR within ±10% for approximately 80% of the population. It's more accurate than the older Harris-Benedict equation for modern populations with higher obesity rates. The formula accounts for the metabolic contributions of weight, height, age, and sex but not body composition directly—two people with identical stats but different muscle-to-fat ratios will get the same BMR estimate despite potentially 100-300 calorie/day real differences.
Revised Harris-Benedict Equation (1984)
The Harris-Benedict equation was originally published in 1919 and revised in 1984 to reflect modern populations. While historically important, it tends to overestimate BMR by 5-10% compared to Mifflin-St Jeor for current populations, particularly for overweight and obese individuals.
For Men:
BMR = 13.397 × weight kg + 4.799 × height cm - 5.677 × age + 88.362
For Women:
BMR = 9.247 × weight kg + 3.098 × height cm - 4.330 × age + 447.593
Katch-McArdle Formula (Best for Lean Individuals)
The Katch-McArdle formula is unique because it calculates BMR based on lean body mass (LBM) rather than total weight, making it more accurate for athletic, muscular individuals or those with known body fat percentages. It's gender-neutral since it accounts for body composition directly.
Formula (Both Genders):
BMR = 370 + (21.6 × lean body mass kg)
Where:
Lean Body Mass = Total Weight × (1 - Body Fat %/100)
Katch-McArdle is superior for athletes and bodybuilders who carry significant muscle mass above population averages. However, it requires accurate body fat measurement—errors in body fat estimation directly translate to BMR errors. DEXA scans provide best accuracy (±1-2% error); bioelectrical impedance and calipers have ±3-5% error; visual estimates can be off by 5-10%, making Katch-McArdle results unreliable without proper body composition testing.
Factors That Affect BMR
- Muscle mass (most significant): Each pound of muscle burns ~6 cal/day at rest vs. ~2 cal/day for fat. Gaining 10 lbs muscle increases BMR by ~40-50 cal/day. Strength training is the most effective way to raise BMR long-term.
- Age-related decline: BMR decreases 1-2% per decade after age 30, primarily from muscle loss. A 25-year-old with 1,800 BMR may have 1,620 BMR at age 60 without intervention. Resistance training mitigates this decline.
- Gender differences: Men have 5-10% higher BMR than women due to greater muscle mass, larger body size, and lower essential body fat requirements. Hormonal differences (testosterone, estrogen) also affect metabolic rate.
- Genetics and ethnicity: BMR varies 10-15% between individuals with identical stats due to genetic factors affecting mitochondrial efficiency, thyroid function, and metabolic pathways. Asian populations tend toward lower BMR than Caucasian populations; genetic testing may eventually personalize estimates.
- Thyroid hormone levels: Hypothyroidism (underactive thyroid) can reduce BMR by 20-40%, causing fatigue and weight gain. Hyperthyroidism (overactive) increases BMR by 20-80%, causing weight loss and elevated heart rate. Thyroid disorders require medical treatment.
- Calorie restriction and metabolic adaptation: Prolonged dieting (500+ calorie deficit for weeks/months) reduces BMR by 10-25% beyond what's expected from weight loss—a survival adaptation. This is why fat loss plateaus occur and post-diet weight regain is common.
- Sleep quality and duration: Poor sleep (<6 hours regularly) reduces BMR by 5-8%, disrupts hunger hormones (ghrelin, leptin), and impairs glucose metabolism. Adequate sleep (7-9 hours) optimizes metabolic function.
- Stress and cortisol: Chronic stress elevates cortisol, which can alter metabolism, promote fat storage (especially visceral belly fat), and impair thyroid function. Stress management supports healthy BMR.
- Menstrual cycle (women): BMR fluctuates ~150 calories across the menstrual cycle, peaking during luteal phase (week before period) due to elevated progesterone. This explains increased hunger and cravings premenstrually.
- Pregnancy and breastfeeding: Pregnancy increases BMR by 300-500 calories/day by third trimester. Breastfeeding burns additional 300-500 calories/day. Post-pregnancy BMR typically returns to pre-pregnancy levels within months.
Using BMR for Weight Management
Calculating Daily Calorie Needs (TDEE)
To determine total daily calorie needs, multiply BMR by an activity factor reflecting exercise and daily movement: Sedentary (1.2), Lightly Active (1.375), Moderately Active (1.55), Very Active (1.725), Super Active (1.9). For example: 1,800 BMR × 1.55 (moderate activity) = 2,790 TDEE. This represents maintenance calories—eating this amount maintains current weight. Most people overestimate activity level; unless exercising intensely 4-6 days weekly, "lightly active" or "moderately active" is appropriate.
Creating Calorie Deficits for Fat Loss
A pound of body fat contains approximately 3,500 calories. To lose 1 lb/week, create a 500 cal/day deficit (3,500 ÷ 7 days). For 2 lbs/week loss, create 1,000 cal/day deficit. For 2,790 TDEE: eat 2,290 cal/day for 1 lb/week loss or 1,790 for 2 lbs/week. Never eat below BMR for extended periods—this can impair metabolic function, cause muscle loss, disrupt hormones, and trigger extreme hunger. Minimum recommended calories: 1,200 for women, 1,500 for men, though individual needs vary. Slower fat loss (0.5-1% bodyweight weekly) preserves muscle better than aggressive deficits.
Creating Calorie Surpluses for Muscle Gain
Building muscle requires a calorie surplus combined with progressive strength training. Aim for 250-500 cal/day above TDEE for lean muscle gain (~0.5-1 lb weekly weight gain). For 2,790 TDEE: eat 3,040-3,290 cal/day. Larger surpluses accelerate weight gain but increase fat accumulation disproportionately—muscle synthesis has biological limits (~2 lbs/month for men, 1 lb/month for women max). Prioritize protein (1.6-2.2 g/kg bodyweight) to optimize muscle protein synthesis. Without strength training, surplus calories become predominantly fat regardless of macronutrient composition.
How to Increase Your BMR
- Build muscle through strength training: Most effective long-term BMR booster. Progressive resistance training 3-5 days/week increases muscle mass, raising BMR by 50-100+ calories/day per 10 lbs muscle gained. Effects persist 24/7, unlike cardio's temporary elevation.
- Eat adequate protein: Protein has highest thermic effect of food (TEF)—20-30% of protein calories burned during digestion vs. 5-10% for carbs, 0-3% for fats. High-protein diets (30% calories) naturally increase daily energy expenditure by 50-100 calories.
- Avoid severe calorie restriction: Deficits >500-750 cal/day for months trigger metabolic adaptation, lowering BMR by 100-400+ calories beyond weight loss. Take diet breaks (2 weeks at maintenance every 8-12 weeks) to restore metabolic rate.
- Increase NEAT (non-exercise activity): While not directly BMR, NEAT (fidgeting, standing, walking, daily movements) can vary by 2,000 calories/day between individuals. Standing desks, walking meetings, and active hobbies increase total expenditure without formal exercise.
- Sleep 7-9 hours nightly: Inadequate sleep reduces BMR, disrupts hunger hormones, impairs insulin sensitivity, and promotes fat storage. Sleep is when growth hormone peaks, supporting muscle recovery and metabolic health.
- Manage stress effectively: Chronic stress elevates cortisol, promoting muscle breakdown, fat storage, and metabolic dysfunction. Stress management (meditation, exercise, hobbies, therapy) supports healthy metabolism.
- Stay hydrated: Mild dehydration (>2% bodyweight) can temporarily reduce metabolic rate by 2-3%. Drinking cold water may slightly boost metabolism as the body warms it to body temperature (~8 calories per 8 oz glass).
- Consider high-intensity interval training (HIIT): HIIT creates an "afterburn effect" (EPOC—excess post-exercise oxygen consumption) that elevates metabolism for 12-24 hours post-workout, burning additional 50-200 calories beyond the workout itself.
- Maintain muscle during weight loss: Prioritize protein (1.8-2.7 g/kg), strength train 3+ days/week, and avoid excessive deficits. Preserving muscle prevents BMR decline that makes fat loss plateaus and regain likely.
- Check thyroid function: If experiencing unexplained fatigue, weight gain, cold intolerance, or other symptoms despite healthy lifestyle, request thyroid panel (TSH, Free T3, Free T4). Hypothyroidism affects 5% of population and is treatable with medication.
Medical Disclaimer
This BMR calculator provides estimates based on validated equations (Mifflin-St Jeor, Harris-Benedict, Katch-McArdle) but cannot account for individual metabolic variations, medical conditions, medications, genetics, or body composition differences beyond what formulas capture. Calculated BMR may vary ±10-20% from actual measured BMR due to genetic factors, thyroid function, medication effects, metabolic adaptations, and other variables. People with thyroid disorders, diabetes, metabolic syndrome, eating disorders, cardiovascular disease, kidney disease, liver disease, or taking medications affecting metabolism should consult endocrinologists or healthcare providers before using BMR estimates for diet planning. Very low-calorie diets (<1,200 cal women, <1,500 cal men), aggressive calorie deficits (>1,000 cal/day), or eating significantly below BMR should only be undertaken with medical supervision to avoid nutrient deficiencies, muscle loss, metabolic damage, gallstones, electrolyte imbalances, and hormonal disruptions. Pregnant and breastfeeding women, children, adolescents, older adults, and competitive athletes have unique calorie needs not fully captured by standard adult BMR formulas. Individual metabolism varies—some people have "fast" metabolisms (BMR 10-15% above predicted), others "slow" (10-15% below). Body composition, NEAT levels, diet history, and genetics all affect actual energy expenditure. This calculator assumes average populations and may not apply equally across all ethnicities—different populations may require adjusted formulas. BMR and TDEE are starting points requiring adjustment based on real-world results—track bodyweight trends over 2-3 weeks and adjust calories by 10-15% if progress doesn't match expectations. Eating disorders, disordered eating patterns, and unhealthy relationships with food/body require professional treatment—do not use calorie calculators as substitutes for therapy. This tool is for educational purposes only, not medical advice, diagnosis, treatment, or nutrition prescription. Always consult registered dietitians, physicians, or certified nutritionists for personalized nutrition guidance, especially when managing medical conditions, eating disorders, or implementing significant calorie changes.
About the Author
Adam
Co-Founder @ RevisionTown
Math Expert specializing in various curricula including IB, AP, GCSE, IGCSE, and more
The basal metabolic rate (BMR) is the amount of energy needed while resting in a temperate environment when the digestive system is inactive. It is the equivalent of figuring out how much gas an idle car consumes while parked. In such a state, energy will be used only to maintain vital organs, which include the heart, brain, kidneys, nervous system, intestines, liver, lungs, sex organs, muscles, and skin. For most people, upwards of ~70% of total energy (calories) burned each day is due to upkeep. Physical activity makes up ~20% of expenditure and ~10% is used for the digestion of food, also known as thermogenesis.
The BMR is measured under very restrictive circumstances while awake. An accurate BMR measurement requires that a person’s sympathetic nervous system is inactive, which means the person must be completely rested. Basal metabolism is usually the largest component of a person’s total caloric needs. The daily caloric need is the BMR value multiplied by a factor with a value between 1.2 and 1.9, depending on activity level.
In most situations, the BMR is estimated with equations summarized from statistical data. The Harris-Benedict Equation was one of the earliest equations introduced. It was revised in 1984 to be more accurate and was used up until 1990, when the Mifflin-St Jeor Equation was introduced. The Mifflin-St Jeor Equation has been shown to be more accurate than the revised Harris-Benedict Equation. The Katch-McArdle Formula is slightly different in that it calculates resting daily energy expenditure (RDEE), which takes lean body mass into account, something that neither the Mifflin-St Jeor nor the Harris-Benedict Equation does. Of these equations, the Mifflin-St Jeor Equation is considered the most accurate equation for calculating BMR with the exception that the Katch-McArdle Formula can be more accurate for people who are leaner and know their body fat percentage. You can pick the equation to be used in the calculation by expanding the settings.
The three equations used by the calculator are listed below:
where:
H is body height in cm
A is age
F is body fat in percentage
BMR Variables
Muscle Mass – Aerobic exercises, such as running or cycling, have no effect on BMR. However, anaerobic exercises, such as weight-lifting, indirectly lead to a higher BMR because they build muscle mass, increasing resting energy consumption. The more muscle mass in the physical composition of an individual, the higher the BMR required to sustain their body at a certain level.
Age – The more elderly and limber an individual, the lower their BMR, or the lower the minimum caloric intake required to sustain the functioning of their organs at a certain level.
Genetics – Hereditary traits passed down from ancestors influence BMR.
Weather – Cold environments raise BMR because of the energy required to create a homeostatic body temperature. Likewise, too much external heat can raise BMR as the body expends energy to cool off internal organs. BMR increases approximately 7% for every increase of 1.36 degrees Fahrenheit in the body’s internal temperature.
Diet – Small, routinely dispersed meals increase BMR. On the other hand, starvation can reduce BMR by as much as 30%. Similar to a phone that goes into power-saving mode during the last 5% of its battery, a human body will make sacrifices such as energy levels, moods, upkeep of bodily physique, and brain functions in order to more efficiently utilize what little caloric energy is being used to sustain it.
Pregnancy – Ensuring the livelihood of a separate fetus internally increases BMR. This is why pregnant women tend to eat more than usual. Also, menopause can increase or decrease BMR depending on hormonal changes.
Supplements – Certain supplements or drugs raise BMR, mostly to fuel weight loss. Caffeine is a common one.
BMR Tests
Online BMR tests with rigid formulas are not the most accurate method of determining an individual’s BMR. It is better to consult a certified specialist or measure BMR through a calorimetry device. These handheld devices are available in many health and fitness clubs, doctor offices, and weight-loss clinics.
Resting Metabolic Rate
While the two are used interchangeably, there is a key difference in their definitions. Resting metabolic rate, or RMR for short, is the rate at which the body burns energy in a relaxed, but not fully inactive state. It is also sometimes defined as resting energy expenditure, or REE. BMR measurements must meet total physiological equilibrium while RMR conditions of measurement can be altered and defined by contextual limitations.
Modern Wisdom
A 2005 meta-analysis study on BMR* showed that when controlling all factors of metabolic rate, there is still a 26% unknown variance between people. Essentially, an average person eating an average diet will likely have expected BMR values, but there are factors that are still not understood that determines BMR precisely.
Therefore, all BMR calculations, even using the most precise methods through specialists, will not be perfectly accurate in their measurements. Not all human bodily functions are well understood just yet, so calculating total daily energy expenditure (TDEE) derived from BMR estimates are just that, estimates. When working towards any sort of health or fitness goal, BMR can aid in laying down the foundations, but from there on, it has little else to offer. A calculated BMR and thus TDEE may result in unsatisfactory results because of their rough estimates, but maintaining a daily journal of exercise, food consumption, etc., can help track the factors that lead to any given results and help determine what works, as well as what needs to be improved upon. Tracking progress in said journal and making adjustments over time as needed is generally the best indication of progress towards reaching personal goals.
