Mifflin-St Jeor Equation | Formula, Worked Examples, and TDEE Application
The Mifflin-St Jeor equation calculates BMR using weight, height, age, and sex. Learn the formula, step-by-step worked examples, TDEE outputs by activity level, and when to use a different equation.
The Mifflin-St Jeor equation is the most widely validated formula for estimating Basal Metabolic Rate (BMR) in healthy adults. Published in 1990 by Mark D. Mifflin and Sachiko T. St Jeor, it uses four inputs: body weight in kilograms, height in centimeters, age in years, and biological sex. The result is a daily calorie estimate representing what the body burns at complete rest.
BMR is the first step in calculating Total Daily Energy Expenditure (TDEE). Once BMR is established using the Mifflin-St Jeor formula, it is multiplied by an activity multiplier to estimate full daily calorie burn. This two-step process is the standard method used in clinical nutrition, registered dietitian software, and the majority of consumer TDEE calculators. For a direct calculation, use the TDEE Calculator.
A 2005 systematic review published in the Journal of the American Dietetic Association compared the Mifflin-St Jeor equation against indirect calorimetry across multiple prediction equations. The review found Mifflin-St Jeor accurate within plus or minus 10% for 82% of healthy adults, a higher accuracy rate than both the original and revised Harris-Benedict equations.
This article covers the full Mifflin-St Jeor formula for males and females, TDEE outputs across all five activity levels, and a comparison against the Harris-Benedict and Katch-McArdle equations.
What Is the Mifflin-St Jeor Equation?
The Mifflin-St Jeor equation is a mathematical formula that estimates Basal Metabolic Rate from four measurable inputs. BMR, also referred to as Resting Metabolic Rate (RMR), is the number of calories the body burns per day to sustain all vital functions while at complete rest. These functions include respiration, cardiac output, organ function, body temperature regulation, and cellular repair.
The equation was developed from a 1990 study of 498 healthy adults conducted by Mifflin and St Jeor and published in the American Journal of Clinical Nutrition. It was designed to improve upon the Harris-Benedict equation, which had been the primary BMR formula since 1919 but was found to overestimate resting metabolic rate by approximately 5% in modern, less-active populations.
Why the Mifflin-St Jeor Equation Replaced the Harris-Benedict Equation as the Standard?
The shift from the Harris-Benedict TDEE formula to Mifflin-St Jeor as the preferred formula reflects a change in population energy expenditure patterns observed between the early twentieth century and today.
The original Harris-Benedict study used a population that was, on average, more physically active than modern sedentary adults
Harris-Benedict produces BMR estimates that are 5 to 15% higher than indirect calorimetry measurements in sedentary individuals
Mifflin-St Jeor was validated against a more representative sample and produces lower, more accurate BMR values for most adults
The 2005 Journal of the American Dietetic Association review confirmed Mifflin-St Jeor's superiority in accuracy for non-obese and obese adults alike
Most registered dietitian software and clinical nutrition tools now use Mifflin-St Jeor as the default BMR calculation method. This TDEE formula is also the calculation engine behind the calculator on this site.
What Does the Mifflin-St Jeor Equation Measure?
The equation estimates resting energy expenditure, the calories burned without any movement or food digestion. It does not account for daily activity, exercise, or the thermic effect of food. Those components are added after BMR is calculated by applying an activity multiplier, which converts BMR into a full TDEE estimate.
Component | What It Measures | Included in Mifflin-St Jeor Output |
|---|---|---|
BMR / RMR | Calories burned at complete rest | Yes — this is what the formula calculates |
NEAT | Calories from non-exercise movement | No — added via activity multiplier |
EAT | Calories burned during planned exercise | No — added via activity multiplier |
TEF | Calories used to digest food | No — not captured in the standard TDEE formula |
TDEE | Total daily calorie burn (all four combined) | No — requires multiplying BMR by activity factor |
Understanding this distinction matters when setting a calorie target. The Mifflin-St Jeor output alone is not a daily calorie target. It is an input to the TDEE formula. For a full breakdown of all four TDEE components, visit the TDEE guide.
What Is the Mifflin-St Jeor Formula?
The Mifflin-St Jeor formula applies a linear equation to weight, height, and age, then adds a fixed sex constant to adjust for average differences in lean mass between biological males and females. The two versions of the formula are structurally identical except for the final constant.
Mifflin-St Jeor Formula for Males
BMR = (10 x weight in kg) + (6.25 x height in cm) - (5 x age in years) + 5
Mifflin-St Jeor Formula for Females
BMR = (10 x weight in kg) + (6.25 x height in cm) - (5 x age in years) - 161
The sex constant of +5 for males and -161 for females captures the average BMR difference attributable to body composition. Males generally carry more lean muscle mass relative to total body weight, which raises resting metabolic rate. The formula applies a fixed adjustment rather than directly measuring lean mass, which is why it performs best when body composition is close to population averages.
What Each Coefficient Represents
Variable | Coefficient | What It Reflects |
|---|---|---|
Weight (kg) | 10 | Each kilogram of body weight adds 10 calories to BMR |
Height (cm) | 6.25 | Each centimeter of height adds 6.25 calories to BMR |
Age (years) | -5 | Each year of age reduces BMR by 5 calories |
Sex constant (male) | +5 | Adjustment for the average male lean mass advantage |
Sex constant (female) | -161 | Adjustment for average female lean mass and hormonal profile |
The weight coefficient carries the largest influence on the final BMR output. A 10 kg difference in body weight produces a 100-calorie difference in BMR and a 155-calorie difference in TDEE at a moderately active multiplier of 1.55.
How to Calculate BMR Using the Mifflin-St Jeor Equation?
Calculating BMR with the Mifflin-St Jeor equation requires four inputs measured accurately. Weight should be recorded in kilograms. Height should be recorded in centimeters. Age should be the current age in full years. Biological sex determines which version of the formula applies.
Worked Example 1: Male, 30 Years Old, 80 kg, 178 cm
BMR = (10 x 80) + (6.25 x 178) - (5 x 30) + 5
BMR = 800 + 1,112.5 - 150 + 5
BMR = 1,767.5 calories per day
Worked Example 2: Female, 35 Years Old, 68 kg, 165 cm
BMR = (10 x 68) + (6.25 x 165) - (5 x 35) - 161
BMR = 680 + 1,031.25 - 175 - 161
BMR = 1,375.25 calories per day
Worked Example 3: Male, 45 Years Old, 95 kg, 183 cm (Heavier, Older)
BMR = (10 x 95) + (6.25 x 183) - (5 x 45) + 5
BMR = 950 + 1,143.75 - 225 + 5
BMR = 1,873.75 calories per day
These BMR values are the inputs to the TDEE formula. They are not daily calorie targets. Each must be multiplied by the correct activity multiplier before being used for nutrition planning. To run this calculation automatically with all five activity level outputs, use the BMR Calculator.
What Is the TDEE Output From the Mifflin-St Jeor Equation?
Once BMR is calculated using the Mifflin-St Jeor formula, it is multiplied by an activity multiplier to produce a TDEE estimate. The five standard activity multipliers originate from the McArdle, Katch, and Katch exercise physiology framework and reflect weekly training volume and daily movement patterns.
TDEE at All Five Activity Levels: Male Example (BMR = 1,767.5)
Activity Level | Multiplier | TDEE Estimate | Best Suited For |
|---|---|---|---|
Sedentary | 1.2 | 2,121 calories | Desk job, no structured exercise, under 5,000 steps per day |
Lightly Active | 1.375 | 2,430 calories | 1-3 gym sessions per week, mostly seated work |
Moderately Active | 1.55 | 2,740 calories | 3-5 gym sessions per week, some daily walking |
Very Active | 1.725 | 3,049 calories | 6-7 training days per week, active lifestyle |
Extra Active | 1.9 | 3,358 calories | Daily intense training plus a physically demanding job |
TDEE at All Five Activity Levels: Female Example (BMR = 1,375.25)
Activity Level | Multiplier | TDEE Estimate | Best Suited For |
|---|---|---|---|
Sedentary | 1.2 | 1,650 calories | Desk job, no structured exercise, minimal daily walking |
Lightly Active | 1.375 | 1,891 calories | Light exercise 1-3 days per week |
Moderately Active | 1.55 | 2,132 calories | Regular gym sessions, some active commuting |
Very Active | 1.725 | 2,372 calories | Hard training 6-7 days per week |
Extra Active | 1.9 | 2,613 calories | Manual labor plus daily training |
How to Set a Calorie Target From the TDEE Output
Knowing your TDEE gives you a maintenance number. From there, setting a goal-specific target is a straightforward adjustment.
Fat Loss: Subtract 400 to 500 calories from TDEE for a sustainable weekly deficit producing approximately 0.5 kg of fat loss per week
Maintenance: Eat at the TDEE estimate; track weight over two to three weeks to confirm accuracy
Lean Muscle Gain: Add 150 to 250 calories above TDEE; this creates a controlled surplus that limits fat accumulation
A one-level error in multiplier selection consistently reduces a planned 500-calorie deficit to approximately 180 to 300 calories. At the sedentary level, overestimating by one level converts a planned deficit into a calorie surplus.
How Accurate Is the Mifflin-St Jeor Equation?
The Mifflin-St Jeor equation is the most accurate general-population BMR formula currently available. The 2005 systematic review in the Journal of the American Dietetic Association found it accurate within plus or minus 10% for 82% of the 494 adults studied. For the remaining 18%, the formula may overestimate or underestimate true BMR by 150 to 400 calories per day.
Factors That Reduce Mifflin-St Jeor Accuracy
The formula performs best when individual body composition matches the population average it was derived from. Accuracy decreases when the following conditions apply.
Condition | How It Affects Accuracy | Magnitude of Error |
|---|---|---|
Body fat above 35% | The formula uses total weight, which over-represents fat mass (low metabolic tissue) | BMR overestimated by 150 to 500 calories |
Body fat below 12% (males) or below 18% (females) | Total weight under-represents lean mass contribution | BMR underestimated by 100 to 250 calories |
Significant metabolic adaptation to dieting | Actual resting metabolic rate drops below formula prediction | True BMR 100 to 300 calories below output |
Age above 65 | Muscle mass loss (sarcopenia) reduces resting metabolic rate faster than the age coefficient captures | BMR overestimated by 50 to 150 calories |
Thyroid dysfunction or hormonal disorders | Metabolic rate varies independently of the formula inputs | Error magnitude varies; use indirect calorimetry |
The accuracy of the activity multiplier is a separate source of error. Selecting a multiplier one level too high creates a TDEE overestimate of 300 to 330 calories per day. This error is often larger than the BMR formula error itself.
How to Validate a Mifflin-St Jeor TDEE Estimate?
The most reliable validation method requires two to three weeks of consistent data collection.
Calculate TDEE using the formula and select the most accurate activity multiplier
Set daily calorie intake exactly at the TDEE estimate
Weigh at the same time each morning before eating or drinking
Calculate the average weekly body weight for each of the two to three weeks
If the average weight is stable, the TDEE estimate is accurate
If weight is falling, actual TDEE is higher than the formula output; increase intake by 100 to 150 calories and retest
If weight is rising, actual TDEE is lower; reduce intake by 100 to 150 calories and retest
This tracking-based validation approach converts a formula estimate into a confirmed personal maintenance number. The formula provides the starting point. Two to three weeks of weight data provides the confirmation.
How Does Mifflin-St Jeor Compare to Harris-Benedict and Katch-McArdle?
Three main equations are used to calculate BMR for TDEE estimation. Each was developed from a different research population, uses different inputs, and produces different accuracy profiles for specific individual types. For a full comparison of all three formulas, visit the TDEE formulas overview page.
Formula Comparison: Inputs, Research Base, and Accuracy Profile
Formula | Year | Research Base | Inputs Required | Best For |
|---|---|---|---|---|
Mifflin-St Jeor | 1990 | 498 healthy adults | Weight, height, age, sex | General healthy adults without body fat measurement |
Harris-Benedict (Revised) | 1919 / revised 1984 | 239 men and women | Weight, height, age, sex | Clinical settings requiring historical consistency |
Katch-McArdle | 1996 | Lean body mass dataset | Lean body mass only | Athletes and individuals with a measured body fat percentage |
Direct Output Comparison Using Identical Inputs
Using a male, age 30, 80 kg, 178 cm as the benchmark:
Formula | BMR Output | TDEE at 1.55 (Moderately Active) | Difference vs Mifflin-St Jeor |
|---|---|---|---|
Mifflin-St Jeor | 1,768 calories | 2,740 calories | Baseline |
Harris-Benedict (Revised) | 1,847 calories | 2,863 calories | +123 calories higher |
Katch-McArdle (at 20% body fat) | 1,757 calories | 2,723 calories | -17 calories lower |
Katch-McArdle (at 10% body fat) | 1,973 calories | 3,058 calories | +318 calories higher |
Katch-McArdle (at 30% body fat) | 1,601 calories | 2,482 calories | -258 calories lower |
At average body composition (approximately 20% body fat for males), all three formulas produce similar outputs. The divergence grows as body composition moves away from population averages. Mifflin-St Jeor and Harris-Benedict converge in accuracy near the population average body fat but diverge significantly at higher or lower body fat percentages.
Mifflin-St Jeor vs. Harris-Benedict: Which Is More Accurate?
The revised Harris-Benedict equation (Roza and Shizgal, 1984) is more accurate than the original 1919 version. But it still overestimates BMR by approximately 5% compared to indirect calorimetry measurements in sedentary adults. The 2005 Journal of the American Dietetic Association review found Mifflin-St Jeor consistently outperformed the revised Harris-Benedict across all subject groups.
For most adults calculating their own TDEE for nutrition planning, Mifflin-St Jeor is the more accurate choice. Harris-Benedict remains appropriate in clinical or research contexts where historical consistency with prior records is required.
Mifflin-St Jeor vs Katch-McArdle: When Does Each Apply?
Katch-McArdle uses lean body mass as its only input. This makes it more accurate than Mifflin-St Jeor for individuals whose body composition differs significantly from population averages, specifically athletes with low body fat and individuals with high body fat.
Use Mifflin-St Jeor when:
No reliable body fat measurement is available
Body composition is close to the population average (15 to 25% body fat for males, 22 to 32% for females)
The individual is a generally healthy adult between the ages of 18 and 65
Use Katch-McArdle when:
A measured body fat percentage is available from DEXA scan, hydrostatic weighing, or calibrated skinfold calipers
Body fat is below 12% (males) or below 18% (females)
Body fat is above 30% and the individual suspects formula overestimation
When Should You Use the Mifflin-St Jeor Equation?
The Mifflin-St Jeor equation is the correct starting formula for most adults in most situations. It requires only four inputs that any person can measure, and it produces an accurate BMR estimate for 82% of healthy adults without needing specialized equipment or laboratory testing.
Situations Where Mifflin-St Jeor Is the Right Formula
Body fat percentage is unknown, estimated, or measured only by bioelectrical impedance
The individual is a generally healthy adult without a diagnosed metabolic disorder
No DEXA scan, hydrostatic weighing, or calibrated skinfold measurement is available
The goal is to establish a starting TDEE estimate for weight loss or maintenance
The individual is switching from a previous calorie approach and wants a validated baseline
Situations Where a Different Formula May Be More Accurate
A lean athlete with body fat below 12% (males) or below 18% (females) who has a reliable body fat measurement should use Katch-McArdle
An individual with body fat above 30% and a reliable body fat measurement will get a more accurate result from Katch-McArdle
A clinical setting that requires consistency with prior records calculated under Harris-Benedict formula may continue using the revised Harris-Benedict formula
The Mifflin-St Jeor equation is the best available general-purpose formula. For most people, it is the appropriate tool. The other formulas address specific accuracy gaps that only become relevant at the extremes of body composition.
How Does Age Affect the Mifflin-St Jeor Output?
The age variable in the Mifflin-St Jeor equation reduces BMR by 5 calories per year. This reflects the gradual decline in resting metabolic rate that accompanies aging, primarily driven by the progressive loss of lean muscle mass (sarcopenia) and reductions in organ metabolic activity.
BMR Decline by Decade: Male, 80 kg, 178 cm
Age | Mifflin-St Jeor BMR | TDEE at 1.55 | Maintenance Calorie Change from Age 25 |
|---|---|---|---|
25 | 1,793 calories | 2,778 calories | Baseline |
35 | 1,743 calories | 2,702 calories | -76 calories |
45 | 1,693 calories | 2,624 calories | -154 calories |
55 | 1,643 calories | 2,547 calories | -231 calories |
65 | 1,593 calories | 2,469 calories | -309 calories |
The 5-calorie-per-year reduction produces a cumulative decline of approximately 50 calories per decade at the BMR level and 77 calories per decade at the TDEE level when using a moderately active multiplier of 1.55. Over 40 years, this adds up to a 309-calorie reduction in daily maintenance needs from the formula alone.
In practice, the age coefficient underestimates BMR decline in older adults who have lost significant lean mass. Individuals over 65 with below-average muscle mass for their age may find that their actual resting metabolic rate is lower than the Mifflin-St Jeor formula predicts.
Recalculating TDEE annually accounts for the formula's age adjustment. Recalculating every three to four kilograms of weight change accounts for the weight coefficient. Both updates together keep the TDEE estimate accurate during periods of fat loss, muscle gain, or aging.
How Does Body Weight Change Affect the Mifflin-St Jeor Output?
The weight coefficient in the Mifflin-St Jeor equation assigns 10 calories of BMR per kilogram. Every kilogram of body weight change, whether from fat loss, muscle gain, or a combination of both, produces a predictable shift in the formula output.
BMR and TDEE Shift Per Kilogram of Body Weight Change
Weight Change | BMR Change | TDEE Change at 1.55 | Practical Effect |
|---|---|---|---|
-5 kg fat loss | -50 calories/day | -77 calories/day | Planned deficit narrows; recalculate to maintain the intended rate of loss |
+3 kg muscle gain | +30 calories/day | +46 calories/day | Maintenance calorie target increases slightly |
-10 kg over a diet phase | -100 calories/day | -155 calories/day | Significant deficit narrowing; recalculation critical at this range |
+5 kg total weight gain | +50 calories/day | +77 calories/day | Maintenance target increases proportionally |
The most common practical error in TDEE-based dieting is using a calorie target calculated at a higher starting weight and not recalculating as weight decreases. A person who loses 10 kilograms and does not update their TDEE estimate is now eating 155 calories more than true maintenance per day, which progressively narrows the planned deficit and eventually stalls fat loss.
Standard practice is to recalculate BMR and TDEE every three to four kilograms of body weight change or every four to six weeks during an active diet or training phase, whichever comes first.
Frequently Asked Questions About the Mifflin-St Jeor Equation
What is the Mifflin-St Jeor equation used for?
The Mifflin-St Jeor equation is used to estimate Basal Metabolic Rate (BMR), which is the number of calories the body burns per day at complete rest. BMR is then multiplied by an activity multiplier to calculate Total Daily Energy Expenditure (TDEE), the number used to set daily calorie targets for fat loss, maintenance, or muscle gain.
How accurate is the Mifflin-St Jeor equation compared to measured resting metabolic rate?
The Mifflin-St Jeor equation is accurate within plus or minus 10% for 82% of healthy adults, according to the 2005 systematic review published in the Journal of the American Dietetic Association. It outperforms the Harris-Benedict equation for general population accuracy. For individuals with atypical body composition, accuracy decreases, and the Katch-McArdle formula based on lean body mass may produce a better estimate.
What is the difference between Mifflin-St Jeor and Harris-Benedict?
Both formulas use weight, height, age, and sex to estimate BMR. Harris-Benedict was published in 1919 and revised in 1984. It consistently overestimates BMR by approximately 5% in modern sedentary populations. Mifflin-St Jeor was developed in 1990 and produces lower, more accurate BMR estimates. Most evidence-based nutrition guidelines and dietitian tools now default to Mifflin-St Jeor.
Should I use Mifflin-St Jeor or Katch-McArdle?
Use Mifflin-St Jeor if body fat percentage is unknown or if body composition is close to the population average. Use Katch-McArdle if a reliable body fat measurement is available and body fat is significantly above or below average. At approximately 20% body fat for males and 28% for females, both formulas produce similar outputs.
Does the Mifflin-St Jeor equation work for older adults?
The equation applies an age coefficient of minus 5 calories per year, which reflects average metabolic decline. For adults over 65 with below-average muscle mass, the formula may overestimate true BMR because sarcopenia accelerates resting metabolic rate decline faster than the fixed coefficient captures. Validating the output with two to three weeks of weight tracking is recommended for this group.
How often should I recalculate using the Mifflin-St Jeor equation?
Recalculate every three to four kilograms of body weight change or every four to six weeks during an active diet or training phase, whichever comes first. Using a TDEE figure calculated at a previous body weight overestimates maintenance and progressively narrows any planned calorie deficit.