BMR Calculator
Estimate your basal metabolic rate—the energy your body uses at rest. Enter your age, sex, height, and weight to calculate an estimated BMR using the Mifflin–St Jeor equation.
Results
Enter your details and calculate to see your estimated BMR.
What Is BMR?
Basal metabolic rate (BMR) is the energy your body uses to maintain essential functions while at rest, including breathing, circulation, temperature regulation, and basic organ function. It is usually expressed as calories per day.
Your BMR is only one part of the energy you use during a full day. It does not include normal movement, exercise, or the full effect of digesting food. For total daily expenditure, use the TDEE Calculator.
How Is BMR Calculated?
A laboratory can measure resting energy expenditure through indirect calorimetry. Online calculators instead use prediction equations based on characteristics associated with energy use. This calculator uses age, height, weight, and the sex category required by the Mifflin–St Jeor equation.
Mifflin–St Jeor Equation
Male
BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5
Female
BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161
Although the result is commonly called BMR in consumer calculators, Mifflin–St Jeor was developed to predict resting energy expenditure (REE). True BMR requires more strictly controlled measurement conditions.
The equation was developed from measurements of 498 adults ages 19 to 78. A later systematic review found that it predicted measured resting metabolic rate within 10% for more adults with and without obesity than several other commonly used equations. This does not mean every individual result will fall within 10% of a measured value.
Mifflin–St Jeor vs Harris–Benedict
Harris–Benedict is an older family of equations used to estimate basal or resting energy expenditure. The original equations were published in the early twentieth century, and revised coefficients were published by Roza and Shizgal in 1984.
Mifflin–St Jeor and Harris–Benedict are separate prediction equations, not different unit conversions. They can produce meaningfully different estimates for the same person. Simple Useful Tools uses Mifflin–St Jeor as the single V1 method so the calculator gives one clearly identified result rather than asking users to choose between technical formulas.
Example BMR Calculation
Example inputs: male, age 30, height 180 cm, weight 80 kg.
BMR = 800 + 1,125 − 150 + 5
BMR = 1,780 calories/day
This means the equation estimates approximately 1,780 calories of resting energy expenditure over 24 hours. It is not an instruction to eat 1,780 calories and does not represent this person's complete daily expenditure.
BMR vs RMR
Basal metabolic rate and resting metabolic rate both describe energy used while the body is at rest, but their measurement conditions differ.
BMR
- Stricter laboratory conditions
- Measured after rest and fasting
- Intended to represent a basal state
RMR/REE
- Less restrictive resting conditions
- Commonly measured or estimated in practical settings
- Often used interchangeably with BMR in public calculators
Mifflin–St Jeor technically predicts resting energy expenditure. This calculator labels the result Estimated BMR because BMR is the term most people use when looking for this calculation, while explaining the distinction rather than presenting BMR and RMR as two falsely precise numbers.
BMR vs TDEE
| Comparison | BMR | TDEE |
|---|---|---|
| Meaning | Energy used at rest | Total energy used during a typical day |
| Activity included | No | Yes |
| Main inputs | Age, height, weight, sex | BMR inputs plus activity level |
| Best used for | Understanding resting energy needs | Estimating full daily expenditure |
If you want to estimate maintenance calories or your complete daily energy expenditure, use the TDEE Calculator.
What Affects Your BMR?
An equation can only use some of the determinants that affect measured resting energy expenditure.
- Body size
- Lean mass and body composition
- Age
- The sex-based coefficient used by the equation
- Genetics
- Hormones and health conditions
- Medications
- Illness or injury
- Pregnancy and breastfeeding
- Environmental temperature
Two people with the same estimated BMR can still have different measured resting energy expenditure. Mifflin–St Jeor does not directly measure lean mass, hormones, health conditions, medication effects, or genetic differences.
Body composition, including the relative amounts of lean mass and body fat, can affect measured resting energy expenditure. If useful, you can separately estimate your body fat percentage with the Body Fat Calculator.
How Accurate Is a BMR Calculator?
A BMR calculator provides a population-based estimate, not a direct measurement. The result may be a useful reference point, but individual resting energy expenditure can be higher or lower.
Indirect calorimetry is the reference method for measuring resting energy expenditure. It estimates energy use from oxygen consumption and carbon dioxide production under controlled conditions.
This calculator may be less representative for people with unusually high or low lean mass, highly trained athletes, pregnant or breastfeeding people, people with conditions or medications that affect metabolism, people who are ill or recovering from injury, and people outside the equation's studied population.
Do not use the result to diagnose a fast or slow metabolism or as a minimum safe calorie intake. A healthcare professional or registered dietitian can help when an individualized assessment is needed.
Sources
- Mifflin MD et al. A new predictive equation for resting energy expenditure in healthy individuals. 1990.
- Frankenfield D, Roth-Yousey L, Compher C. Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults. 2005.
- Harris JA, Benedict FG. A Biometric Study of Human Basal Metabolism.
- Roza AM, Shizgal HM. The Harris Benedict equation reevaluated. 1984.
- Delsoglio M et al. Indirect Calorimetry in Clinical Practice. 2019.
Frequently Asked Questions
What is a good BMR for my age?
Should I eat my BMR calories to lose weight?
Why does my BMR seem low?
Does BMR change when you lose weight?
Is BMR the number of calories I burn in a day?
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