BMR & TDEE Calculator Guide: Estimate Resting Metabolism and Daily Energy Expenditure
Basal metabolic rate and total daily energy expenditure answer two different questions. BMR describes the energy required to sustain essential physiological functions under highly controlled resting conditions, while total daily energy expenditure includes the energy used across an entire day.
Resting metabolic rate or resting energy expenditure is closely related to BMR but is generally measured under less restrictive conditions. NCBI clinical references describe BMR as energy expenditure under tightly controlled basal conditions and RMR as a similar measure obtained under less restrictive resting conditions.
For consumer calculators, BMR and RMR are usually estimated rather than directly measured. Prediction equations use variables such as body weight, height, age, and sex to estimate resting energy expenditure from population data.
The Mifflin–St Jeor equation is one of the most widely used prediction equations. It was developed from resting energy expenditure measurements in 498 adults and uses weight, height, age, and sex to predict resting energy needs.
The original Mifflin–St Jeor study reported that the older Harris–Benedict equations overestimated resting energy expenditure in its sample. Later validation studies have produced mixed results across different populations, which is one reason no prediction equation should be treated as individually exact.
Measured resting energy expenditure can differ from a predicted result by a meaningful amount. Indirect calorimetry, which measures respiratory gas exchange, remains the reference method for measuring resting energy expenditure in clinical practice.
TDEE adds another layer of uncertainty because total daily expenditure depends not only on resting metabolism but also on physical activity, exercise, occupation, spontaneous movement, and the thermic effect of food.
A common consumer approach estimates TDEE by multiplying predicted BMR or RMR by an activity factor. This is convenient, but the activity factor is itself an approximation. Two people who both describe themselves as moderately active can have substantially different actual daily energy expenditure.
FAO and WHO energy-requirement guidance uses physical activity level, or PAL, as the ratio of total energy expenditure to basal metabolic rate. In that framework, total expenditure can be estimated by multiplying BMR by an appropriate PAL.
This calculator therefore presents TDEE as an estimated range rather than pretending an activity label such as “moderately active” produces a laboratory-quality measurement.
The result is most useful as a starting point. If the goal is calorie or macronutrient planning, the estimated TDEE can flow into the Calorie & Macro Calculator.
How to Estimate BMR, RMR, and TDEE Without Treating Prediction Equations as Exact Measurements
- Enter your age: Use your current age in completed years. Age contributes to the prediction equation because resting expenditure tends to differ across the lifespan.
- Enter your height: Use an accurate standing-height measurement. The calculator converts U.S. customary units to centimeters where necessary.
- Enter your current weight: Use a recent body-weight measurement. Short-term fluid changes can alter scale weight without representing a change in metabolic tissue.
- Select the equation input sex: Mifflin–St Jeor uses different constants for male and female equation groups because the original prediction model was developed that way.
- Review the predicted resting expenditure: Treat this as an estimate of resting energy needs rather than a directly measured metabolic rate.
- Choose an activity assumption: Select the activity description that most closely matches your average lifestyle, occupation, and exercise—not your most active day.
- Review the estimated TDEE range: Because activity classification is imprecise, use the result as a starting range rather than an exact maintenance-calorie prescription.
- Compare actual body-weight trends over time: If intake and weight are tracked consistently, real-world trends can provide useful feedback about whether the initial TDEE estimate is too high or too low.
Formula and variables
W is body weight in kilograms, H is height in centimeters, and A is age in years. The Mifflin–St Jeor equation predicts resting energy expenditure. TDEE is then estimated by multiplying the resting estimate by an activity factor or physical-activity-level assumption. The second step adds considerable uncertainty because actual daily activity differs among individuals.
Mifflin–St Jeor: Male REE = 10W + 6.25H − 5A + 5; Female REE = 10W + 6.25H − 5A − 161; Estimated TDEE = Predicted REE × Activity Factor- W — Body weight
- Current body weight expressed in kilograms for the equation.
- H — Height
- Standing height expressed in centimeters.
- A — Age
- Age in completed years.
- REE — Predicted resting energy expenditure
- Estimated calories used per day under resting conditions.
- AF — Activity factor
- A multiplier used to approximate the relationship between resting expenditure and total daily expenditure.
- TDEE — Total daily energy expenditure
- Estimated total calories expended across an average day.
Scenario 1: Mifflin–St Jeor Estimate for a 35-Year-Old Adult
A 35-year-old male equation user weighs 80 kg and is 180 cm tall. The calculator first predicts resting energy expenditure using Mifflin–St Jeor and then applies an illustrative activity factor of 1.55.
- Age
- 35 years
- Weight
- 80 kg
- Height
- 180 cm
- Equation
- Mifflin–St Jeor male equation
- Illustrative activity factor
- 1.55
- REE = 10 × 80 + 6.25 × 180 − 5 × 35 + 5.
- REE = 800 + 1,125 − 175 + 5.
- Predicted REE ≈ 1,755 kcal/day.
- Illustrative TDEE = 1,755 × 1.55.
- Estimated TDEE ≈ 2,720 kcal/day.
Result: The Mifflin–St Jeor resting estimate is approximately 1,755 kcal/day. Using an illustrative 1.55 activity factor produces an estimated TDEE of about 2,720 kcal/day.
The 1,755-calorie result is a prediction of resting expenditure, not a measured metabolic rate. The 2,720-calorie TDEE contains additional uncertainty because the activity multiplier approximates rather than directly measures daily movement and exercise.
Understanding your results
Predicted BMR or REE
This estimates daily energy use at rest from population-derived equations.
It is not the number of calories a person should automatically eat.
Estimated TDEE
This adds an activity assumption to the resting estimate.
It is a starting estimate of maintenance energy expenditure rather than a guaranteed maintenance intake.
Activity multiplier
This expresses how much higher total expenditure is assumed to be relative to resting expenditure.
The label is approximate and should not be interpreted as a measured physical-activity level.
Maintenance-calorie estimate
Energy intake near actual TDEE would theoretically maintain body-energy stores over time when other conditions are stable.
Short-term body weight can still fluctuate substantially from water, glycogen, digestive contents, sodium intake, and other factors.
Equation comparison
If multiple prediction equations are displayed, differences among them show model uncertainty rather than an error in arithmetic.
Measured resting expenditure can also differ from every prediction equation.
Assumptions
- The calculator is intended primarily for adults.
- Height, weight, age, and equation inputs are accurate.
- Mifflin–St Jeor is being used as a predictive equation rather than a direct measurement.
- Activity remains approximately similar to the selected average level.
- The TDEE multiplier represents a planning assumption.
- The result does not account individually for every difference in body composition, hormones, disease, medications, genetics, ambient temperature, or adaptive changes in metabolism.
- Pregnancy and breastfeeding are excluded from the ordinary adult TDEE model.
- The calculator does not prescribe a calorie deficit or surplus automatically.
Limitations
- Mifflin–St Jeor predicts resting energy expenditure rather than measuring it.
- The original Mifflin study derived its equation from 498 healthy adults and found a substantial amount of individual variability around the regression model.
- Prediction equations can overestimate or underestimate measured energy expenditure for particular individuals and populations.
- Indirect calorimetry remains the reference method for measuring resting energy expenditure in clinical settings.
- BMR and RMR or REE are related but not perfectly interchangeable concepts. BMR requires more restrictive measurement conditions.
- Activity multipliers used by consumer calculators are simplifications and should not be presented as directly measured PAL values.
- A person who exercises several times per week but sits for most of the day can have a different TDEE from someone with the same workouts and a physically demanding occupation.
- Fitness trackers and exercise machines can also misestimate calorie expenditure.
- Energy expenditure changes with body weight and can adapt during prolonged changes in calorie intake. NIDDK specifically warns against static calorie rules that ignore metabolic adaptation.
- A fixed TDEE estimate should therefore not be projected indefinitely through substantial weight loss or gain.
- Pregnant or breastfeeding people require additional energy considerations and should not rely on an ordinary adult maintenance-calorie calculator. NIDDK excludes these groups from its standard Body Weight Planner.
- Children and adolescents have energy requirements related to growth and should not be treated as smaller adults using a simple adult TDEE multiplier. FAO notes that growth contributes to pediatric energy requirements.
- People with serious illness, eating disorders, major metabolic conditions, or specialized clinical nutrition needs require individualized professional assessment.
Common mistakes
- Calling predicted BMR a measured metabolic rate.
- Using BMR and TDEE interchangeably.
- Eating exactly at the BMR number because it is labeled daily calories.
- Treating an activity multiplier as precise.
- Choosing a high activity category because of one or two workouts while ignoring an otherwise sedentary day.
- Counting exercise calories twice by using a high activity factor and then adding workout calories again.
- Using exercise-machine calorie estimates as though they were laboratory measurements.
- Assuming TDEE remains unchanged after substantial weight loss.
- Assuming people with the same height, weight, age, and sex must have identical metabolism.
- Using a prediction equation during pregnancy as though pregnancy creates no additional physiological demands.
- Using an adult equation as a clinical pediatric energy prescription.
- Treating the difference between two equations as evidence that one calculator is broken.
Practical use cases
Scenario 2: Estimate maintenance calories before setting macros
A user wants to plan protein, fat, and carbohydrate intake.
BMR/TDEE provides an estimated maintenance-energy baseline before the Calorie & Macro Calculator allocates that energy to a goal and macronutrient structure.
Scenario 3: Compare sedentary and active weeks
The user normally works at a desk but temporarily begins a physically demanding job.
The same resting-energy estimate can produce a materially different TDEE when daily activity changes.
Scenario 4: Compare predicted with measured metabolism
A person undergoes indirect calorimetry through a clinical or sports setting.
The measured value can replace the prediction-equation result as the stronger resting-energy input while activity expenditure still requires separate estimation.
Scenario 5: Weight changes substantially
A user loses 15 kg over time.
The original resting and total-expenditure estimate should be recalculated using the new body weight rather than being treated as permanently fixed.
Scenario 6: Body composition is known
A user has a reasonably credible body-fat estimate and wants to compare a lean-mass-based equation with Mifflin–St Jeor.
The Body Fat Calculator can provide a field estimate, but any lean-mass-based metabolic calculation inherits the error of that body-composition estimate.
Planning and decision guide
BMR describes energy needed for basic physiological function
Basal energy expenditure supports functions such as breathing, circulation, cellular maintenance, and other essential processes.
Strict BMR measurement requires controlled resting conditions.
RMR or REE is similar but measured under less restrictive conditions
NCBI clinical references distinguish RMR from BMR primarily through the measurement conditions.
Consumer calculators often use the terms loosely, so this page should explain which prediction equation is actually being used.
Scenario 7: Calculator says BMR but equation predicts REE
Mifflin–St Jeor was developed as a resting energy expenditure equation.
Calling its result an exact laboratory BMR would overstate what the equation measures.
Mifflin–St Jeor uses weight, height, age, and sex
The original equation was derived using resting energy expenditure measured in adults.
Its simplified sex-specific forms remain widely used.
Male Mifflin–St Jeor equation
The commonly used simplified form is 10 × weight in kg + 6.25 × height in cm − 5 × age + 5.
The result is expressed as approximate kcal per day of resting expenditure.
Female Mifflin–St Jeor equation
The commonly used simplified form is 10 × weight in kg + 6.25 × height in cm − 5 × age − 161.
The equation’s sex term reflects how the original statistical model was structured.
Prediction equations explain only part of individual variation
The original Mifflin model reported an R² of approximately 0.71.
That is useful at a population level but leaves substantial individual variation unexplained.
Scenario 8: Two similar adults have different measured REE
Age, height, weight, and equation sex are nearly identical.
Their actual measured energy expenditure can still differ because a prediction equation does not capture every physiological variable.
Mifflin is not the only prediction equation
Harris–Benedict, revised Harris–Benedict, Owen, WHO/FAO/UNU, Cunningham, and other equations are also used in research and practice.
Their predictions can differ for the same person.
A systematic review previously favored Mifflin for many healthy adults
A widely cited systematic review found Mifflin–St Jeor predicted resting metabolic rate within 10% of measurement more often than several other common equations in the populations examined.
Later research has also shown that equation performance varies by population, so no equation should be presented as universally best.
More recent research reinforces population dependence
A 2023 critical appraisal found Harris–Benedict performed particularly well in the white-adult reference population used in that analysis.
This illustrates why prediction-equation rankings can change with the sample studied.
Scenario 9: Two equations differ by 150 calories
The arithmetic of both formulas can be correct.
The difference represents model assumptions and population fit rather than a guaranteed 150-calorie error in one direction.
Indirect calorimetry is stronger when precise resting expenditure is clinically important
Indirect calorimetry estimates energy expenditure from respiratory gas exchange and is regarded as the reference or gold-standard clinical measurement method.
Prediction equations are substitutes when direct measurement is impractical.
Measured does not mean perfectly immutable
Resting expenditure varies with measurement conditions and physiology.
Even indirect calorimetry requires standardized testing conditions for reliable interpretation.
TDEE includes more than formal exercise
Total expenditure includes resting metabolism plus physical activity and the energetic effects associated with daily living and food processing.
Occupation, walking, household activity, spontaneous movement, and workouts all contribute.
Scenario 10: Same gym routine, different occupations
Two people each lift weights four times per week.
One sits at a computer all day while the other performs physically demanding work. Their actual total expenditure can differ substantially despite identical exercise frequency.
PAL is formally defined as TEE divided by BMR
FAO/WHO/UNU energy-requirement guidance defines physical activity level as total 24-hour energy expenditure divided by basal metabolic rate.
Multiplying BMR by PAL therefore yields estimated total energy expenditure.
Consumer activity factors are approximate PAL proxies
Labels such as sedentary, lightly active, moderately active, very active, and extremely active are convenient user-interface categories.
They should be described as estimates rather than official individualized physiological measurements.
Activity labels should include behavioral descriptions
A number such as 1.55 means little without context.
Describe occupation, daily movement, and typical exercise patterns so users can choose based on actual behavior.
Avoid promising one universal multiplier table
Different calculators publish slightly different activity-factor conventions.
The website should document the multipliers it uses and allow users to see how changing the factor changes TDEE.
Scenario 11: 1.4 versus 1.6
A resting estimate of 1,700 kcal produces about 2,380 kcal/day at 1.4 and about 2,720 kcal/day at 1.6.
A small-looking multiplier choice can therefore shift estimated maintenance intake by hundreds of calories.
Activity-factor uncertainty can exceed equation differences
Users often debate which BMR equation differs by 50 or 100 kcal.
Selecting an inaccurate activity category can create a much larger TDEE error.
Exercise should not be double counted
If the chosen activity factor already represents regular exercise, adding the full estimated workout calories on top can overstate TDEE.
Either use an activity-adjusted multiplier or build expenditure from separate components consistently.
Scenario 12: High activity factor plus exercise calories
The calculator already assumes frequent exercise through the multiplier.
Adding another 600 kcal for every workout can count part of the same activity twice.
Fitness-device calorie estimates are also estimates
Wearables can provide useful activity trends but their calorie estimates are not equivalent to whole-day laboratory energy-expenditure measurement.
Do not automatically overwrite TDEE with one device number without understanding its method.
Maintenance calories are inferred from energy balance over time
A predicted TDEE provides a starting hypothesis.
Consistent body-weight trends under reasonably tracked intake can provide empirical information about whether the estimate is too high or too low.
Scenario 13: Estimated maintenance is 2,500 but weight declines
The user consistently eats near 2,500 kcal and body weight declines over several weeks.
Actual average expenditure may be higher than the original estimate, intake may be undercounted, or both.
Short-term scale changes are noisy
Water, glycogen, sodium, food volume, menstrual-cycle effects, and bowel contents can change body weight quickly.
Use longer-term trends rather than interpreting one or two days as evidence that TDEE is wrong.
Energy expenditure changes when body weight changes
A smaller body often requires less energy to maintain and move than a larger body.
The original TDEE estimate should therefore be recalculated after meaningful weight change.
The static 3,500-calorie rule is too simplistic for long-term weight prediction
NIDDK’s Body Weight Planner uses a dynamic model because energy expenditure and body weight adapt over time.
NIDDK specifically explains that the body responds to calorie changes and weight loss slows relative to a simple static rule.
Scenario 14: Fixed 500-calorie deficit for one year
A simple arithmetic model assumes the same deficit continues producing the same rate of loss indefinitely.
In reality, changes in body mass and metabolism reduce the energy gap over time.
The Calorie & Macro Calculator should use TDEE as a starting input
BMR/TDEE determines the estimated energy baseline.
The Calorie & Macro Calculator can then apply a clearly defined goal assumption and divide energy among protein, fat, and carbohydrate.
TDEE should not automatically become a weight-loss recommendation
Maintenance estimation and calorie-target selection are separate calculations.
This page should stop at estimated expenditure rather than silently imposing a calorie deficit.
Scenario 15: User only wants maintenance
The calculator estimates current expenditure.
It should not label a lower number as the recommended intake unless the user explicitly enters a weight-management goal on the appropriate page.
Protein requirements should also remain separate
Protein targets depend on additional factors beyond TDEE, including body size, activity, training, life stage, and the goal of the calculation.
Use the Protein Intake Calculator for that specific question.
Body composition can improve context but not eliminate uncertainty
Lean-mass-based equations can incorporate fat-free mass when it is known.
Their usefulness depends heavily on the accuracy of the body-composition measurement.
The Body Fat Calculator produces an estimate, not laboratory lean mass
A circumference-derived body-fat estimate can provide useful context.
But using that estimate in another metabolic equation compounds the measurement uncertainty.
Pregnancy should be excluded from the standard TDEE output
Pregnancy changes energy needs through maternal tissue changes, fetal growth, and other physiological demands.
NIDDK explicitly excludes pregnant and breastfeeding users from its standard adult Body Weight Planner.
Children require growth energy
FAO notes that adult energy requirements can be approximated from TEE, while children also require energy for growth.
A simple adult TDEE equation therefore should not be used as a pediatric nutrition prescription.
Clinical illness can substantially alter energy expenditure
Critical illness, fever, trauma, endocrine disorders, and other medical conditions can change energy needs and can reduce the usefulness of ordinary prediction equations.
Clinical nutrition decisions can require indirect calorimetry or specialized equations.
The strongest result shows uncertainty rather than false precision
Display predicted resting expenditure, chosen activity factor, estimated TDEE, and a reasonable sensitivity range.
A result such as 2,718 kcal/day should not imply that actual expenditure has been measured to the nearest calorie.
Frequently asked questions
What is BMR?
Basal metabolic rate is the energy used to maintain essential physiological functions under carefully controlled basal resting conditions.
What is RMR?
Resting metabolic rate is closely related to BMR but is measured under somewhat less restrictive resting conditions.
What is REE?
Resting energy expenditure is the amount of energy expended at rest and is commonly expressed in kilocalories per day.
Are BMR and RMR the same?
They are closely related but technically differ in measurement conditions. Consumer calculators often use the terms interchangeably even though the distinction exists.
What is TDEE?
Total daily energy expenditure is the total energy used across a day, including resting metabolism and physical activity.
What is the difference between BMR and TDEE?
BMR or resting expenditure describes energy use at rest. TDEE includes the rest of the energy expended during daily life.
How do I calculate BMR?
A prediction equation such as Mifflin–St Jeor uses weight, height, age, and sex to estimate resting energy expenditure.
What is the Mifflin–St Jeor equation?
For the male equation: 10 × kg + 6.25 × cm − 5 × age + 5. For the female equation: 10 × kg + 6.25 × cm − 5 × age − 161.
Is Mifflin–St Jeor accurate?
It is a widely studied prediction equation, but individual error can be meaningful. The original model explained only part of individual variation, and later studies show accuracy differs among populations.
What is the most accurate BMR equation?
There is no universally most accurate predictive equation for every individual and population. Indirect calorimetry is the reference method when accurate measurement is clinically important.
Is Harris–Benedict better than Mifflin?
Results vary by population and study. Some validation work favors Mifflin in broad adult samples, while other research has found Harris–Benedict performs well in particular populations.
What is indirect calorimetry?
It measures respiratory gas exchange to estimate energy expenditure and is regarded as the clinical reference method for measuring resting energy expenditure.
Is my calculator BMR a measured metabolism?
No. A calculator using age, height, weight, and sex predicts resting expenditure from an equation.
How do I calculate TDEE?
A common estimate multiplies predicted resting expenditure by an activity factor or physical activity level.
What is a TDEE activity multiplier?
It is a planning multiplier intended to represent how much total daily expenditure exceeds resting expenditure because of movement and activity.
Are activity multipliers accurate?
They are approximations. People within the same activity label can have substantially different occupations, movement patterns, and exercise loads.
What does sedentary mean in a TDEE calculator?
It generally represents relatively low daily physical activity beyond ordinary living. The exact multiplier and definition depend on the calculator.
Should I count my workouts separately?
Not if your selected activity factor already incorporates your normal exercise and the calculator is designed around that approach, because doing both can double count activity.
What are maintenance calories?
They are an estimate of calorie intake that would roughly match total energy expenditure over time when body weight and activity are relatively stable.
Is TDEE the number of calories I should eat?
Not necessarily. TDEE estimates expenditure. Intake goals depend on whether your objective is maintenance, weight change, athletic performance, or a clinical nutrition plan.
Should I eat at my BMR?
BMR is not a daily calorie target. It represents estimated resting energy needs and excludes much of the energy used during ordinary daily activity.
Why is my TDEE higher than my BMR?
Because TDEE includes movement, exercise, occupational activity, and other components of daily energy expenditure in addition to resting metabolism.
Can TDEE change?
Yes. It changes with body weight, activity, exercise, occupation, physiology, and other factors.
Does losing weight lower TDEE?
It often can because a smaller body generally requires less energy to maintain and move, and metabolic adaptations can also occur.
Should I recalculate TDEE after losing weight?
Yes after meaningful weight change or major changes in activity because the original inputs and energy requirements may no longer apply.
Why does my fitness watch show a different TDEE?
Wearables use their own algorithms and sensor data, while a calculator uses prediction equations and activity assumptions. Neither is equivalent to direct laboratory measurement.
Does muscle increase BMR?
Body composition influences resting energy expenditure, but a simple Mifflin calculation does not directly measure lean mass.
Can body-fat percentage improve BMR estimates?
Some equations use fat-free mass, but their result depends on how accurately body composition is measured.
Can athletes use BMR calculators?
They can use them as rough starting estimates, but unusually high lean mass and activity can make ordinary population equations less representative.
Can older adults use Mifflin–St Jeor?
The equation includes age, but prediction accuracy can vary in older populations, particularly when body composition differs substantially from the original equation sample.
Can children use this TDEE calculator?
This adult calculator should not be used as a pediatric energy prescription because children also require energy for growth.
Can I use this calculator during pregnancy?
Standard adult TDEE calculations do not account adequately for pregnancy-related energy needs. Pregnancy requires life-stage-specific guidance.
Can I use this while breastfeeding?
Standard adult maintenance calculations do not include the additional energy requirements associated with lactation.
Can illness change my energy needs?
Yes. Illness, fever, injury, endocrine conditions, medications, and other clinical factors can substantially change energy expenditure.
How does BMR relate to BMI?
They measure different things. BMI relates weight to height, while BMR equations estimate resting energy expenditure. Use the BMI Calculator for weight-status screening.
What should I do after calculating TDEE?
If your goal is nutrition planning, use the estimate as an input to the Calorie & Macro Calculator rather than assuming TDEE itself defines your calorie or macro target.
How accurate is a BMR and TDEE calculator?
The formulas are calculated exactly, but the physiological estimates can differ substantially from actual expenditure because resting-energy equations and activity factors are predictive approximations.
Sources and review
- A New Predictive Equation for Resting Energy Expenditure in Healthy Individuals — American Journal of Clinical Nutrition / PubMed. Accessed 2026-09-01.
- Comparison of Predictive Equations for Resting Metabolic Rate in Healthy Nonobese and Obese Adults: A Systematic Review — Journal of the American Dietetic Association / PubMed. Accessed 2026-09-01.
- Predicting Resting Energy Expenditure: A Critical Appraisal — European Journal of Clinical Nutrition / PubMed. Accessed 2026-09-01.
- Indirect Calorimetry in Clinical Practice — Clinical Nutrition / PubMed. Accessed 2026-09-01.
- Human Energy Requirements — Basal Metabolic Rate and Physical Activity Level — Food and Agriculture Organization of the United Nations. Accessed 2026-09-01.
- Human Energy Requirements — Physical Activity Level — Food and Agriculture Organization of the United Nations. Accessed 2026-09-01.
- About the Body Weight Planner — National Institute of Diabetes and Digestive and Kidney Diseases. Accessed 2026-09-01.
- NIH Body Weight Planner — National Institute of Diabetes and Digestive and Kidney Diseases. Accessed 2026-09-01.
Reviewed 2026-09-01 by Dr Akawak Ejigu, DBA.