BMR Calculator
Estimate your basal metabolic rate with the Mifflin-St Jeor equation and the calories you burn per day at five activity levels.
About BMR (Basal Metabolic Rate):
BMR represents the minimum number of calories your body needs to maintain basic physiological functions like breathing, circulation, and cell production while at rest.
- BMR tends to fall with age, partly because muscle mass declines
- Men usually have a higher BMR than women of the same weight because they carry more lean mass
- Lean tissue uses more energy at rest than fat tissue
- Two people with the same age, height and weight can still differ noticeably in measured BMR
- Long periods of severe calorie restriction can lower resting energy use
- Fever, some medications and thyroid conditions change BMR in ways no equation captures
Formula used: Mifflin-St Jeor equation (1990). Results are estimates for healthy adults; a clinician can measure resting energy use directly if you need an exact figure.
Updated Formula covered by automated tests
Basal metabolic rate is the energy your body spends in a day just to stay alive at complete rest: keeping the heart beating, the lungs moving, the brain running and body temperature steady. For most adults it is the largest single slice of daily energy use, bigger than exercise. This calculator estimates it from age, sex, height and weight with the Mifflin-St Jeor equation, then multiplies it by standard activity factors to estimate how many calories you burn on a typical day.
People look up their BMR when setting up a meal plan, when a fitness app asks for a calorie target, or when they want to understand why a smaller, older body needs less food than it once did. The activity table turns the resting figure into a practical maintenance number, and the weight goal row shows what eating 250 or 500 calories either side of it would look like.
The formula
- weight
- Body weight in kilograms; pound entries are multiplied by 0.45359237
- height
- Standing height in centimeters; inch entries are multiplied by 2.54
- age
- Age in whole years; each extra year lowers the estimate by 5 kcal per day
- +5 / −161
- Sex constant from the original study; the 166 kcal gap reflects the average difference in lean mass between men and women of the same size
- activity factor
- Multiplier from 1.2 (desk job, little exercise) to 1.9 (hard daily training or heavy manual work) that scales resting energy up to a full day
Mark Mifflin, Sachiko St Jeor and colleagues published the equation in 1990 after measuring resting energy expenditure by indirect calorimetry in 498 healthy adults, both normal-weight and obese. They found that weight, height, age and sex explained most of the variation, and that the older Harris-Benedict equation from 1919 tended to overestimate modern adults.
A 2005 systematic review by Frankenfield and colleagues for the American Dietetic Association compared the common prediction equations against measured values and judged Mifflin-St Jeor the most reliable for healthy adults, which is why many dietitians use it as the default. Strictly, the equation predicts resting metabolic rate, which is slightly higher than a true basal measurement taken after an overnight fast in a lab, but the two terms are used interchangeably in everyday nutrition.
Worked example
Priya is a 35-year-old woman, 165 cm tall, who weighs 68 kg. She walks to work and goes to the gym three or four times a week, so she picks the moderately active level.
- 1 Weight term: 10 × 68 = 680.
- 2 Height term: 6.25 × 165 = 1031.25.
- 3 Age term: 5 × 35 = 175, which is subtracted.
- 4 Add the female constant: 680 + 1031.25 − 175 − 161 = 1375.25 kcal per day.
- 5 Apply the moderate activity factor: 1375.25 × 1.55 = 2131.6, which rounds to 2132 kcal.
Result: Priya’s estimated BMR is about 1,375 kcal per day and her maintenance intake about 2,132 kcal. A man with the same age, height and weight would get 1,541 kcal, exactly 166 more.
Before you rely on the result
- The equation predicts an average for people of your size, and individuals can sit well above or below it. Indirect calorimetry is the only way to measure your own value.
- It does not use body composition, so very muscular people are usually underestimated and people with high body fat can be overestimated.
- It was developed in healthy adults. Pregnancy, breastfeeding, thyroid disorders, recovery from illness and many medications change energy needs; ask a doctor or registered dietitian in those situations.
Frequently asked questions
What is the difference between BMR and TDEE?
BMR covers only resting functions. Total daily energy expenditure (TDEE) adds the energy used to digest food and everything you do while awake, from fidgeting to running. The activity rows in the results are TDEE estimates: BMR multiplied by a factor between 1.2 and 1.9.
Should I eat fewer calories than my BMR to lose weight?
Generally no. Diets that go below resting needs are hard to sustain and make it difficult to get enough protein and micronutrients. A modest reduction from your maintenance (TDEE) figure is the usual approach, and very low calorie diets should only be followed under medical supervision.
Why did my estimate drop when I entered a higher age?
The equation subtracts 5 kcal for each year of age, reflecting the gradual loss of lean tissue and organ mass seen in population data. Ten years therefore lowers the estimate by 50 kcal per day. Staying physically active and doing resistance training can slow the underlying muscle loss.
Which activity level should I choose?
Pick the level that matches an average week rather than your best week. Most people with office jobs who exercise a few times a week belong in lightly or moderately active. If your weight stays stable for a month at the suggested intake, the level is about right; if it drifts, adjust by one step.
Sources
- Mifflin MD, St Jeor ST et al. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr, 1990 (pubmed.ncbi.nlm.nih.gov)
- Frankenfield D et al. Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review. J Am Diet Assoc, 2005 (pubmed.ncbi.nlm.nih.gov)