BMR — Basal Metabolic Rate (Mifflin–St Jeor)
Step-by-step derivation
Provide inputs to see the working with your numbers.
Mifflin–St Jeor reference
Sources
• General dietetics references for BMR vs. TDEE concepts.
Use this BMR Calculator to estimate your basal metabolic rate with the Mifflin–St Jeor equation. It gives a quick estimate of how many calories your body uses each day at rest based on your sex, age, height, and weight.
Reviewed by: AjaxCalculators Editorial Team
Last updated: May 2, 2026
Method source: Mifflin–St Jeor predictive equation for resting energy expenditure / basal metabolic rate
Editorial standards: AjaxCalculators Editorial Policy
What This BMR Calculator Calculates
This calculator estimates your basal metabolic rate (BMR), which is the number of calories your body uses each day at rest to support basic life functions.
These basic functions include:
- breathing
- circulation
- cell maintenance
- temperature regulation
- brain and nervous system function
- basic organ function
The calculator uses the Mifflin–St Jeor method and is designed as a quick starting estimate for adults. It does not calculate full daily maintenance calories by itself because maintenance calories also require activity and daily movement to be included.
What BMR Means
BMR stands for basal metabolic rate. It is an estimate of how much energy your body uses at rest before adding exercise, job activity, walking, chores, digestion, or other daily movement.
BMR is often used as a starting point for calorie planning because it helps estimate your baseline energy needs. To estimate full daily calorie needs, BMR is usually adjusted upward with an activity factor to estimate TDEE, or total daily energy expenditure.
How the BMR Calculator Works
This calculator uses the Mifflin–St Jeor equation. The equation estimates resting calorie use from sex, age, height, and weight.
Male Formula
BMR = 9.99 × weight(kg) + 6.25 × height(cm) − 4.92 × age(years) + 5
Female Formula
BMR = 9.99 × weight(kg) + 6.25 × height(cm) − 4.92 × age(years) − 161
The result is shown in kcal/day. That is your estimated daily calorie use at rest before most daily movement and exercise are added.
Formula Summary
| Input or Result | Formula or Meaning | Important Note |
|---|---|---|
| Male BMR | 9.99W + 6.25H − 4.92A + 5 | Uses weight in kg, height in cm, and age in years |
| Female BMR | 9.99W + 6.25H − 4.92A − 161 | Uses weight in kg, height in cm, and age in years |
| W | Weight | Converted to kilograms internally if needed |
| H | Height | Converted to centimeters internally if needed |
| A | Age | Entered in full years |
| BMR result | Estimated kcal/day at rest | Does not include exercise or daily activity |
BMR vs RMR vs TDEE
BMR, RMR, and TDEE are related terms, but they are not exactly the same.
| Term | Full Name | What It Means |
|---|---|---|
| BMR | Basal metabolic rate | Estimated energy used at rest under very controlled conditions |
| RMR | Resting metabolic rate | Resting energy use measured or estimated under less strict conditions than BMR |
| TDEE | Total daily energy expenditure | Total daily calories after activity, movement, and digestion are included |
| Maintenance calories | Estimated calories to maintain weight | Usually estimated from TDEE, not BMR alone |
Many online calculators use BMR and RMR wording closely because both refer to resting calorie needs. For daily calorie planning, the BMR estimate is usually only the first step.
What Affects BMR?
The Mifflin–St Jeor equation uses age, sex, height, and weight, but real resting energy expenditure can vary between people for many reasons.
| Factor | Typical Effect on BMR Estimate | Why It Matters |
|---|---|---|
| Body weight | Higher weight usually increases the estimate | More body mass generally requires more energy to maintain |
| Height | Greater height usually increases the estimate | Height is part of the body-size estimate |
| Age | Higher age usually lowers the estimate | The equation subtracts calories as age increases |
| Sex selection | Changes the formula constant | The equation uses different male and female constants |
| Body composition | Not directly measured by this calculator | People with the same weight may have different muscle and fat mass |
| Health and medications | Not included in the equation | Some conditions and medications can affect appetite, weight, or metabolism |
Worked Example: Female BMR Estimate
Suppose a woman enters:
- Age: 30 years
- Height: 165 cm
- Weight: 65 kg
Step 1: Use the female Mifflin–St Jeor formula
BMR = 9.99 × weight + 6.25 × height − 4.92 × age − 161
Step 2: Substitute the values
BMR = 9.99 × 65 + 6.25 × 165 − 4.92 × 30 − 161
Step 3: Calculate each part
9.99 × 65 = 649.35
6.25 × 165 = 1031.25
4.92 × 30 = 147.6
Step 4: Combine the values
BMR = 649.35 + 1031.25 − 147.6 − 161
Step 5: Calculate the result
BMR ≈ 1372 kcal/day
Result: This person’s estimated basal metabolic rate is about 1372 calories per day.
Worked Example: Male BMR Estimate
Suppose a man enters:
- Age: 35 years
- Height: 178 cm
- Weight: 82 kg
Step 1: Use the male Mifflin–St Jeor formula
BMR = 9.99 × weight + 6.25 × height − 4.92 × age + 5
Step 2: Substitute the values
BMR = 9.99 × 82 + 6.25 × 178 − 4.92 × 35 + 5
Step 3: Calculate each part
9.99 × 82 = 819.18
6.25 × 178 = 1112.50
4.92 × 35 = 172.20
Step 4: Combine the values
BMR = 819.18 + 1112.50 − 172.20 + 5
Step 5: Calculate the result
BMR ≈ 1764 kcal/day
Result: This person’s estimated basal metabolic rate is about 1764 calories per day.
Worked Example: Why BMR Is Not Maintenance Calories
Suppose a person has an estimated BMR of 1372 kcal/day. That number represents resting calorie use, not full daily calorie needs.
If that person moves around, works, exercises, digests food, and performs normal daily activities, total daily energy use will be higher than BMR.
| Calorie Estimate | What It Includes | Example Use |
|---|---|---|
| BMR | Resting body functions only | Baseline calorie estimate |
| TDEE | BMR plus activity and daily movement | Maintenance calorie planning |
| Weight-loss target | Usually below estimated TDEE | Fat-loss planning |
| Weight-gain target | Usually above estimated TDEE | Weight-gain planning |
To estimate maintenance calories, use a maintenance calorie or TDEE calculator that applies an activity factor to the BMR/RMR estimate.
How to Use This BMR Calculator
- Select your sex as used by the calculator’s equation.
- Enter your age in full years.
- Enter your height in centimeters or feet and inches.
- Enter your weight in kilograms or pounds.
- Click Calculate if the tool requires it.
- Review your estimated BMR in kcal/day.
- Use the result as a resting calorie estimate, not as your full daily calorie target.
How to Interpret the Result
Your BMR result is your estimated calorie requirement at rest only. It does not include normal walking, workouts, work activity, household tasks, digestion, or most daily movement.
| Result Pattern | Common Explanation | Important Reminder |
|---|---|---|
| Higher BMR | Larger body size, younger age, or male formula constant may increase the estimate | It is still only an estimate |
| Lower BMR | Smaller body size, older age, or female formula constant may lower the estimate | It does not automatically mean poor health |
| BMR lower than expected | Equation inputs may differ from your body composition or real metabolism | Indirect calorimetry is needed for measurement |
| BMR used as maintenance calories | This usually underestimates full daily needs | TDEE is needed for maintenance planning |
If you want a fuller daily calorie estimate, use your BMR as the starting point and then apply an activity factor through a maintenance calorie or TDEE calculator.
How to Convert BMR Into a Maintenance Estimate
BMR alone is not enough to estimate full daily calorie needs. A basic maintenance estimate usually multiplies BMR or RMR by an activity factor:
TDEE = BMR × activity factor
| Activity Level | Common Multiplier | Typical Description |
|---|---|---|
| Sedentary | 1.2 | Little exercise, mostly sitting, low daily movement |
| Lightly active | 1.375 | Light exercise or regular easy movement |
| Moderately active | 1.55 | Moderate exercise several days per week |
| Very active | 1.725 | Hard exercise, active job, or frequent training |
| Extra active / athlete-style | 1.9 | Very hard training, physical job, or high-volume activity |
Activity multipliers are broad estimates. Real daily energy use can differ because of job movement, exercise intensity, steps, standing time, training volume, and individual metabolism.
Why BMR Calculators Are Estimates
No online BMR calculator can measure your exact metabolic rate. The equation gives a prediction based on averages from the variables entered.
| Reason for Difference | Why It Matters |
|---|---|
| Body composition | Muscle mass and fat mass can differ between people with the same weight |
| Metabolic adaptation | Recent dieting, weight loss, or weight gain can affect energy expenditure |
| Health conditions | Some conditions can affect weight, appetite, fluid balance, or metabolism |
| Medication effects | Some medications can affect appetite, weight, heart rate, or energy use |
| Measurement error | Incorrect height, weight, age, or unit selection changes the result |
| Individual variation | People with similar inputs can still have different resting energy expenditure |
For a measured resting metabolic rate, clinical or laboratory testing such as indirect calorimetry is typically required.
Mifflin–St Jeor vs Harris–Benedict
The Mifflin–St Jeor and Harris–Benedict equations are both used to estimate resting calorie needs, but they are different formulas.
| Equation | What It Uses | Common Use |
|---|---|---|
| Mifflin–St Jeor | Sex, age, height, and weight | Common modern BMR/RMR calculator method |
| Harris–Benedict | Sex, age, height, and weight | Traditional calorie-needs calculations |
| Activity-adjusted equation | BMR/RMR multiplied by activity factor | Maintenance calorie or TDEE estimate |
Different equations can give different results for the same person. That is normal because all predictive equations use assumptions and population averages.
Who Should Be Careful With BMR Estimates?
Some people should not rely on calculator-generated calorie estimates without professional guidance.
- Children and teenagers
- Pregnant or breastfeeding people
- People with a current or past eating disorder
- People with diabetes or blood-sugar management needs
- People with kidney, liver, thyroid, heart, or gastrointestinal conditions
- People taking medications that affect appetite, weight, fluid balance, or metabolism
- People with unexplained weight loss or rapid weight gain
- Competitive athletes with high training demands
- Anyone advised by a clinician to follow a specific nutrition plan
In these cases, a doctor, registered dietitian, or qualified healthcare professional can help interpret energy needs more safely.
When This Calculator Is Useful
This calculator is useful when you need a general adult resting calorie estimate and understand that the output is only a starting point.
- Estimating resting calorie needs
- Getting a starting point before calculating maintenance calories
- Comparing how age, height, and weight affect estimated BMR
- Understanding the difference between BMR and TDEE
- Cross-checking numbers from calorie and TDEE calculators
- Preparing questions for a doctor, dietitian, trainer, or coach
When You May Need More Than This Calculator
A simple BMR calculator may not be enough when medical, performance, or clinical nutrition needs are involved.
Use a more individualized method when working with:
- medical weight-loss plans
- eating disorder recovery
- pregnancy or breastfeeding nutrition
- diabetes or blood-sugar management
- kidney disease, heart disease, thyroid disease, or chronic illness
- sports performance nutrition
- bodybuilding contest preparation
- very low calorie intake
- rapid or unexplained weight change
- clinical nutrition or prescribed diets
Common Mistakes to Avoid
- Treating BMR as full daily calories: BMR does not include most daily movement or exercise.
- Forgetting activity level: maintenance calories require an activity adjustment.
- Entering the wrong units: mixing pounds with kilograms or inches with centimeters can change the result.
- Using an incorrect age: the equation changes as age changes.
- Assuming the result is exact: BMR equations estimate averages, not individual measurements.
- Ignoring health context: medical conditions and medications can affect calorie needs.
- Using adult formulas for children: children and teens have growth-related energy needs.
- Using BMR alone for weight loss: calorie targets should be based on TDEE, nutrition quality, and health context.
- Cutting below safe intake levels: very low calorie intake should be medically supervised.
Important Assumptions and Limitations
- This calculator uses the Mifflin–St Jeor predictive equation.
- The result is an estimate, not a measured metabolic rate.
- The calculator is intended for general adult planning.
- It estimates resting calorie use only, not full daily calorie needs.
- It does not include activity, exercise, digestion, job movement, or training load.
- It does not account for pregnancy, breastfeeding, chronic illness, medications, athletic periodization, metabolic adaptation, or clinical nutrition needs.
- It does not diagnose metabolic conditions, malnutrition, obesity, or eating disorders.
- It does not replace individualized guidance from a doctor, registered dietitian, or qualified healthcare professional.
Practical Uses of a BMR Calculator
- Estimate baseline resting calorie needs
- Compare how age, height, weight, and sex affect estimated BMR
- Use BMR as the first step toward TDEE estimation
- Cross-check calorie calculator outputs
- Support general nutrition planning discussions
- Understand why maintenance calories are usually higher than BMR
- Prepare for more detailed calorie tracking or dietitian consultation
References
- Endotext / NCBI Bookshelf: Estimating Resting Metabolic Rate with the Mifflin–St Jeor Equation
- National Academies / NCBI Bookshelf: Factors Affecting Energy Expenditure and Requirements
- Dietary Reference Intakes for Energy: Summary
- StatPearls / NCBI Bookshelf: Total Daily Energy Expenditure
- CDC: Adult BMI Calculator and Screening Note
Related Calculators
- Maintenance Calorie Calculator
- Harris-Benedict Calculator
- Calorie Calculator
- Calorie Deficit Calculator
- Weight Gain Calculator
- BMI Calculator
Frequently Asked Questions
What is BMR?
BMR means basal metabolic rate. It estimates how many calories your body uses at rest for basic functions such as breathing, circulation, temperature regulation, and organ function.
What formula does this BMR Calculator use?
This calculator uses the Mifflin–St Jeor equation, which estimates resting calorie needs from sex, age, height, and weight.
Is BMR the same as RMR?
They are closely related but not exactly the same. BMR is usually measured under stricter resting conditions, while RMR is measured under less strict resting conditions. Online calculators often use these terms closely for resting calorie estimates.
Is BMR the same as maintenance calories?
No. BMR estimates resting calorie use only. Maintenance calories usually refer to TDEE, which includes activity, daily movement, and digestion.
How do I calculate maintenance calories from BMR?
A common method is to multiply BMR by an activity factor. The formula is TDEE = BMR × activity factor.
Why is my BMR lower than my daily calorie needs?
BMR does not include most daily movement, exercise, work activity, or digestion. Your full daily calorie needs are usually higher than BMR.
How accurate is a BMR calculator?
It gives a starting estimate, not an exact measurement. Real resting energy expenditure can differ because of body composition, health, medications, genetics, and individual variation.
Can I use BMR for weight loss?
BMR can be a starting reference, but weight-loss planning usually uses TDEE rather than BMR alone. Health context and professional guidance matter, especially for medical conditions or very low calorie targets.
Can children or teens use this BMR Calculator?
This calculator is intended for adults. Children and teens have growth-related nutrition needs and should use appropriate pediatric guidance.
Why do different BMR calculators give different results?
Different calculators may use different equations, constants, rounding rules, or activity assumptions. All predictive equations should be treated as estimates.
Can I measure my real BMR?
Resting metabolic rate can be measured more directly with clinical or laboratory methods such as indirect calorimetry. An online calculator estimates rather than measures.
Should I follow the BMR number exactly?
No. Treat it as a baseline estimate. Full calorie planning should consider activity, nutrition quality, body-weight trends, health status, and professional guidance when needed.
Disclaimer: This BMR Calculator provides an educational estimate of basal metabolic rate or resting metabolic rate using the Mifflin–St Jeor equation. Results depend on the sex, age, height, weight, unit selections, and formula assumptions entered. BMR is an estimate of resting calorie use only and does not include normal daily movement, exercise, job activity, digestion, pregnancy, breastfeeding, illness, medication effects, metabolic adaptation, or individual differences in body composition. The result is not a measured metabolic rate, medical diagnosis, or personalized nutrition prescription. This calculator is intended for general adult planning only. It should not replace advice from a doctor, registered dietitian, or qualified healthcare professional, especially for users under 18, pregnancy, breastfeeding, eating disorders, diabetes, thyroid disease, kidney disease, chronic illness, medication-managed conditions, unexplained weight change, clinical nutrition needs, or medically supervised weight management.