BMR Calculator
Estimate your Basal Metabolic Rate and Total Daily Energy Expenditure using the Mifflin-St Jeor formula, the equation most widely recommended for the general population.
Basal Metabolic Rate (BMR) is the number of calories your body burns at complete rest just to keep your heart beating, lungs breathing, and cells functioning — typically 60–75% of total daily calories burned. The Mifflin-St Jeor formula calculates it as BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5 for men, and the same formula with −161 instead of +5 for women.
Your results
Based on the Mifflin-St Jeor formula.
Calories burned at complete rest.
- Harris-Benedict (1984)
- 1,854 kcal
- Katch-McArdle
- Enter body fat %
How to use this calculator
Choose your unit system. Select metric (kilograms, centimeters) or imperial (pounds, feet and inches), depending on which measurements you have on hand.
Enter sex, age, height, and weight. These four values are required inputs for the Mifflin-St Jeor formula.
Optionally enter body fat percentage. Adding it unlocks the Katch-McArdle comparison, which is based on lean body mass rather than total body weight.
Select your activity level. Choose the option that best matches your typical week to estimate TDEE from your BMR.
Read your BMR and TDEE. The calculator updates instantly with your estimated BMR, TDEE, and a comparison across three formulas.
What is BMR?
Basal Metabolic Rate is the amount of energy, measured in calories, that your body needs to carry out its most basic life-sustaining functions while at complete physical and digestive rest. It is measured under strict conditions: after 8 hours of sleep, a 12-hour fast, and no physical activity beforehand.
BMR fuels processes that continue whether you are awake or asleep: circulating blood, breathing, regulating body temperature, growing and repairing cells, and running your nervous system. It specifically excludes the energy used to digest food (the thermic effect of food), and any energy used for movement, exercise, or daily activity — those are counted separately in TDEE.
What BMR physiologically covers
- Organ function
- The brain, liver, kidneys, and heart alone typically account for roughly half of BMR, despite being a small fraction of body weight.
- Cellular maintenance
- Ongoing cell repair, protein turnover, and maintaining ion gradients across cell membranes.
- Circulation and respiration
- The baseline energy cost of a beating heart and breathing lungs.
- Thermoregulation
- Maintaining core body temperature at rest.
The Mifflin-St Jeor formula
Published by Mifflin and St Jeor in 1990, this equation is the formula most widely recommended for estimating BMR in the general adult population, including by the Academy of Nutrition and Dietetics.
| Sex | Formula |
|---|---|
| Men | BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age(yr) + 5 |
| Women | BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age(yr) − 161 |
Worked example
A 30-year-old man who weighs 80 kg and is 180 cm tall:
- 10 × 80 (weight in kg) = 800
- 6.25 × 180 (height in cm) = 1,125
- 5 × 30 (age in years) = 150
- 800 + 1,125 − 150 + 5 = 1,780
Mifflin-St Jeor vs. Harris-Benedict vs. Katch-McArdle
All three formulas estimate the same underlying quantity but weight the inputs differently. The table below applies each formula to the same 30-year-old, 80 kg, 180 cm man (15% body fat for Katch-McArdle) used in the worked example above.
| Formula | Source | Requires | Result (example) |
|---|---|---|---|
| Mifflin-St Jeor | Mifflin & St Jeor, 1990 | Weight, height, age, sex | 1,780 kcal/day |
| Harris-Benedict | Harris & Benedict, 1919; revised 1984 | Weight, height, age, sex | 1,854 kcal/day |
| Katch-McArdle | Katch & McArdle | Weight, body fat % | 1,839 kcal/day |
Mifflin-St Jeor is generally considered the most accurate for people of average body composition, while the original 1919 Harris-Benedict formula tends to overestimate BMR for modern populations, which is why most calculators use the 1984 revision. Katch-McArdle can be the most accurate option for lean, muscular, or very high body-fat individuals because it is based on lean body mass rather than total weight.
From BMR to TDEE
Total Daily Energy Expenditure (TDEE) is your BMR multiplied by an activity factor that accounts for movement, exercise, and the energy cost of digesting food. TDEE represents the calories you burn in an average full day, not just at rest.
| Activity level | Multiplier | Description |
|---|---|---|
| Sedentary | ×1.2 | Little or no exercise, desk job |
| Light | ×1.375 | Light exercise 1–3 days/week |
| Moderate | ×1.55 | Moderate exercise 3–5 days/week |
| Very active | ×1.725 | Hard exercise 6–7 days/week |
| Extra active | ×1.9 | Very hard training plus a physically demanding job |
Worked example
Using the same 30-year-old man (BMR = 1,780 kcal/day) at a moderate activity level:
- 1,780 (BMR) × 1.55 (moderate multiplier) = 2,759
Factors that affect BMR
Muscle mass
Muscle tissue is more metabolically active than fat tissue, so more lean mass generally means a higher BMR at the same body weight.
Age
BMR tends to decline gradually with age, largely due to loss of muscle mass and shifts in hormone levels over time.
Sex
Men typically have a higher BMR than women of the same age, height, and weight, mainly due to differences in average muscle mass and body composition.
Body size and surface area
Taller and heavier individuals generally have a higher BMR, since larger bodies require more energy to maintain.
Hormones
Thyroid hormones directly regulate metabolic rate; conditions like hypothyroidism and hyperthyroidism can lower or raise BMR significantly.
Genetics
Individual metabolic rate varies by an estimated 5–10% between people of otherwise similar age, sex, and body composition, for reasons not fully explained by measurable factors.
Dieting and energy restriction
Prolonged calorie restriction can trigger adaptive thermogenesis, a drop in BMR beyond what would be predicted by weight loss alone.
Pregnancy and lactation
Both meaningfully increase energy needs above standard BMR formulas, which are not designed for these conditions.
Common mistakes people make with BMR and TDEE
Treating BMR as an eating target
BMR is a survival minimum, not a calorie goal. Weight-loss targets should be set below TDEE, not below BMR.
Overestimating activity level
Most people select a more active category than their real week matches, which inflates TDEE and can stall weight loss.
Using BMR and TDEE interchangeably
They are different numbers for different purposes: BMR is calories at rest, TDEE is total calories across a full day.
Never recalculating
BMR and TDEE change as weight, age, and activity change; a number calculated a year ago may no longer be accurate.
Ignoring lean body mass when it's known
If body fat percentage is known, Katch-McArdle often reflects individual metabolism more closely than weight-only formulas.
What this calculator can and cannot do
It can
Provide a population-based estimate of BMR and TDEE, accurate to within roughly 10% for most healthy adults, and let you compare three established formulas side by side.
It cannot
Measure your actual metabolism (only indirect calorimetry can do that), account for medical conditions, medications, pregnancy, or hormonal disorders, or replace individualized advice from a doctor or registered dietitian.
FAQ
What is BMR (Basal Metabolic Rate)?
BMR is the number of calories your body burns at complete rest to maintain basic life functions such as breathing, circulation, and cell repair. It does not include digestion, movement, or exercise.
How is BMR different from RMR (Resting Metabolic Rate)?
BMR is measured under strict laboratory conditions after an overnight fast and full rest, while RMR is measured under less strict conditions and is typically 5–10% higher. In everyday use and in most online calculators, the two terms are used interchangeably.
How is BMR different from TDEE?
BMR is the calories your body burns at complete rest. TDEE adds the calories burned through daily movement, exercise, and digestion on top of BMR. TDEE is calculated by multiplying BMR by an activity factor.
Which BMR formula is most accurate?
The Mifflin-St Jeor equation, published in 1990, is considered the most accurate formula for the general population and is recommended by the Academy of Nutrition and Dietetics. Katch-McArdle can be more accurate for people who know their body fat percentage, since it accounts for lean body mass directly.
How do I calculate my BMR by hand?
For men: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years) + 5. For women: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years) − 161.
Is it safe to eat below my BMR?
Eating consistently below your BMR is generally not recommended without medical supervision, since your body needs at least that many calories to run basic organ functions. Extended very low calorie intake can affect hormones, muscle mass, and metabolic rate.
Does muscle mass affect BMR?
Yes. Muscle tissue burns more calories at rest than fat tissue, so people with more lean muscle mass generally have a higher BMR than people of the same weight with a higher body fat percentage.
Does BMR decrease with age?
Yes. BMR tends to decline gradually with age, largely due to a natural loss of muscle mass over time. This is one reason calorie needs are often recalculated every few years.
How accurate is an online BMR calculator?
Prediction equations like Mifflin-St Jeor are typically accurate to within 10% of measured BMR for most people, but individual metabolism can vary. The only way to measure BMR precisely is indirect calorimetry in a clinical setting.
What is a normal or average BMR range?
Most adults have a BMR between roughly 1,200 and 2,000 calories per day, though this varies widely with body size, sex, muscle mass, and age. There is no single normal number that applies to everyone.
How often should I recalculate my BMR?
Recalculate your BMR whenever your weight changes by more than a few kilograms or pounds, roughly every 4–8 weeks during active weight loss or gain, or any time your activity level changes significantly.
Can I use my BMR to lose weight?
BMR itself is not a target to eat at. Instead, use your TDEE (BMR multiplied by an activity factor) as your maintenance calories, then create a moderate deficit below TDEE, while staying at or above your BMR, for sustainable weight loss.
Does this calculator account for pregnancy, medical conditions, or medications?
No. This calculator uses general population formulas and does not account for pregnancy, lactation, thyroid disorders, medications, or other medical conditions that can change metabolic rate. Consult a doctor or registered dietitian for a personalized assessment.
Medical disclaimer
This calculator provides general estimates based on population averages and published prediction equations. It is not medical advice, a diagnostic tool, or a substitute for guidance from a qualified doctor or registered dietitian.
If you are pregnant or breastfeeding, have a diagnosed medical condition, take medication that affects metabolism, or have a history of disordered eating, consult a healthcare professional before making changes to your calorie intake based on these results.