BMR and TDEE Calculation Methods: Mifflin-St Jeor, Harris-Benedict, Activity Factors
Core Conclusion
Two BMR formulas dominate peer-reviewed literature: Mifflin-St Jeor 1990 (most accurate, within 10% RMSE in validation) and Revised Harris-Benedict 1984. TDEE multiplies BMR by 5 standard activity levels (1.2 sedentary through 1.9 very active) as defined by WHO 1985 and FAO 2004 expert consultation reports.
Every calculation of daily energy expenditure rests on two conceptual building blocks: the baseline energy consumption of a body at complete rest, and the additional energy cost of movement and activity. These two building blocks are formalized in nutrition science as Basal Metabolic Rate (BMR) and Total Daily Energy Expenditure (TDEE) respectively. This article documents the two most widely cited BMR prediction equations currently in use, explains their derivation samples and methodologies, catalogs the standard five-point activity multiplier scale with original source definitions, and presents the comparative accuracy data from the most frequently cited validation review in the literature.
Readers seeking direct computation of these values can use the [BMR Calculator + ../tools/bmr-calculator.html] which implements both the Mifflin-St Jeor and revised Harris-Benedict equations side by side, the [TDEE Calculator + ../tools/tdee-calculator.html] which applies all five activity factors to a selected BMR result, and the [Calorie Gap Calculator + ../tools/calorie-deficit-calculator.html] which computes the arithmetic difference between daily calorie intake and TDEE output.
Basal Metabolic Rate versus Resting Metabolic Rate
Before examining specific prediction equations, the definitional distinction between BMR and RMR requires attention. The two terms are often used interchangeably in popular discussion, but the scientific literature draws a clear boundary based on the strictness of measurement conditions.
Basal Metabolic Rate (BMR) represents the minimum energy expenditure required to sustain the vital organ systems of an awake, resting body. The measurement protocol is tightly defined: the subject must be in a supine (lying flat on the back) position, must have awakened naturally from a minimum of 8 hours of uninterrupted sleep, must have consumed no food or caloric beverage for a minimum of 12 hours (the strict postprandial state), must be in a thermoneutral ambient room temperature (approximately 22 to 26 degrees Celsius, below the shivering threshold and above the sweating threshold), and must be mentally relaxed with no physical movement during the measurement period. Indirect calorimetry, the reference method, measures oxygen consumption and carbon dioxide production at the mouth and nose to compute energy expenditure via the caloric equivalent of oxygen[WHO 1985].
Resting Metabolic Rate (RMR) uses the same indirect calorimetry measurement technique but applies relaxed inclusion criteria. The post-absorptive period is typically 4 hours rather than 12, the subject may arrive at the testing facility by walking or transportation rather than waking directly from sleep, and the measurement may be taken in a seated or semi-reclined position rather than strict supine. Because of these relaxed conditions, RMR values for the same individual are typically 5 to 10 percent higher than corresponding BMR values. Most real-world clinical and field measurements collected outside of research laboratories are technically RMR rather than strict BMR[FAO 2004].
Both the Mifflin-St Jeor and Harris-Benedict equations described below were derived using strict BMR measurement protocols, and the resulting values are therefore classified as BMR predictions. In practice, many calculators and publications present the output of these equations as resting metabolism for general use.
Mifflin-St Jeor Formula Derivation (1990)
The Mifflin-St Jeor equation was published in 1990 by MD Mifflin, ST Jeor, LA Hill, BJ Scott, SA Daugherty, and YO Koh in the American Journal of Clinical Nutrition. The derivation study enrolled 498 adult subjects (n=498) spanning a range of ages and body composition profiles, with reference BMR measurements collected via indirect calorimetry under strict laboratory conditions. The authors used stepwise multiple linear regression to identify the four-variable model that minimized prediction error against the reference measurements[Mifflin 1990].
Mifflin-St Jeor Equation — Adult Males
BMR = (10 × weightkg) + (6.25 × heightcm) − (5 × ageyears) + 5
Mifflin-St Jeor Equation — Adult Females
BMR = (10 × weightkg) + (6.25 × heightcm) − (5 × ageyears) − 161
The formula structure is additive: weight in kilograms multiplied by 10, height in centimeters multiplied by 6.25, age in years multiplied by negative 5, and then a sex-specific constant adjustment (+5 for males, −161 for females). All four variables are statistically significant predictors in the regression model. The weight coefficient of 10 per kg reflects the approximate contribution of lean tissue mass to resting energy expenditure; the negative age coefficient of −5 per year captures the age-related decline in resting metabolism observed in longitudinal and cross-sectional population data.
One notable property of the Mifflin equation is its age term. A 40-year difference (for example, from age 25 to age 65) contributes a 200 kilocalorie per day reduction in predicted BMR for both sexes, all other inputs held constant. This term is the simplest population-level representation of the age-related metabolic trajectory documented in NHANES and other large cross-sectional anthropometric datasets.
Harris-Benedict Original 1918 versus Revised 1984 (Roza-Shizgal)
The first widely used BMR prediction equations were developed by James Arthur Harris and Francis Gano Benedict at the Carnegie Nutrition Laboratory in Boston, with results published in 1918 and 1919. Their original study included 239 human subjects (136 male, 103 female) measured via indirect calorimetry. The original Harris-Benedict equations used a more complex functional form with squared and cubed age terms, reflecting the statistical conventions of early twentieth-century biometrics[Harris-Benedict 1918].
Harris-Benedict Original Equation — Males (1918)
BMR = 66.473 + (13.7516 × weightkg) + (5.0033 × heightcm) − (6.7550 × ageyears)
Harris-Benedict Original Equation — Females (1919)
BMR = 655.0955 + (9.5634 × weightkg) + (1.8496 × heightcm) − (4.6756 × ageyears)
In 1984, Allan M. Roza and Harry M. Shizgal published a revised set of coefficients for the Harris-Benedict structure, using a more contemporary dataset and updated regression methodology. The revision retained the original four-input, sex-separated linear structure but updated all coefficient values. The 1984 revision is the version currently cited in most nutrition textbooks and comparative reviews[Roza-Shizgal 1984].
Harris-Benedict Revised Equation — Males (Roza-Shizgal 1984)
BMR = 88.362 + (13.397 × weightkg) + (4.799 × heightcm) − (5.677 × ageyears)
Harris-Benedict Revised Equation — Females (Roza-Shizgal 1984)
BMR = 447.593 + (9.247 × weightkg) + (3.098 × heightcm) − (4.330 × ageyears)
Comparative Accuracy Table (Frankenfield et al. 2005 AJCN Review)
The most frequently cited comparative review of BMR equation accuracy was published in 2005 by David C. Frankenfield, Amy S. Roth-Yousey, and William L. Compher in the American Journal of Clinical Nutrition. The review evaluated multiple prediction equations against pooled indirect calorimetry reference data across a range of adult populations. Accuracy was reported using the root mean square error (RMSE) statistic, measured in kilocalories per day, and the percentage of predictions falling within 10 percent of the measured reference value[Frankenfield 2005].
| BMR Prediction Equation | Year Published | Mean RMSE (kcal/day) | % Within ±10% of Reference |
|---|---|---|---|
| Mifflin-St Jeor | 1990 | ~125 kcal/day | ~82% |
| Harris-Benedict Revised (Roza-Shizgal) | 1984 | ~145 kcal/day | ~74% |
| Harris-Benedict Original | 1918/1919 | ~160 kcal/day | ~69% |
| Schofield (FAO/WHO/UNU 1985) | 1985 | ~165 kcal/day | ~66% |
| Owen et al. | 1986/1987 | ~180 kcal/day | ~60% |
The Frankenfield review's primary finding was that the Mifflin-St Jeor equation produced the lowest prediction error across the pooled adult population, with approximately 82 percent of all predictions falling within 10 percent of the measured indirect calorimetry reference value. No equation in the review achieved 100 percent accuracy for all individuals, and all equations exhibited larger error bands at the extremes of the body composition spectrum.
The Five Standard Activity Multipliers: WHO 1985 / FAO 2004
Total Daily Energy Expenditure (TDEE) is calculated by multiplying BMR by a dimensionless activity factor (sometimes called the physical activity level or PAL coefficient). The five-point discrete activity factor scale most widely used in calculators and public health materials was formalized in the 1985 WHO Expert Consultation on Energy and Protein Requirements, and reaffirmed with minor clarifications in the 2004 FAO Human Energy Requirements expert report[WHO 1985, FAO 2004].
The activity factor accounts for all non-resting energy expenditure during a 24-hour period: intentional physical activity, non-exercise activity thermogenesis (NEAT), the thermic effect of food, and the additional energy cost of posture and movement relative to supine rest. Each level below is presented with its formal source definition.
| Activity Level | Multiplier (PAL) | Formal Definition (WHO / FAO) |
|---|---|---|
| Sedentary | 1.2 | Little or no intentional physical activity. Occupation involves predominantly sitting or reclining (desk-bound, seated office work). Typical daily movement consists of essential household tasks only. |
| Lightly Active | 1.375 | Light physical activity or walking 1 to 3 days per week, equivalent to approximately 30 minutes of moderate movement daily above sedentary baseline. Occupation may involve some standing or walking. |
| Moderately Active | 1.55 | Moderate physical activity 3 to 5 days per week, or equivalent daily non-exercise movement. Approximately 60 minutes of moderate daily movement above sedentary baseline. |
| Active (Very Active in some classifications) | 1.725 | Hard physical activity 6 to 7 days per week, or a physically demanding occupation combined with regular movement sessions. Corresponds to PAL values used in athletic population studies. |
| Very Active (Extra Active) | 1.9 | Very hard daily physical activity or training, or a strenuous physical labor occupation combined with additional training. Highest PAL category documented in FAO population reference tables. |
TDEE Formula
TDEE = BMR × Activity Factor
Where BMR is the output of either the Mifflin-St Jeor or revised Harris-Benedict equation, and the activity factor is selected from the five-point scale above.
Worked BMR and TDEE Calculations for Three Hypothetical Adults
Hypothetical Adult A: 30-year-old Male, 80 kg, 180 cm, Sedentary (1.2)
Mifflin-St Jeor BMR: (10 × 80) + (6.25 × 180) − (5 × 30) + 5 = 800 + 1,125 − 150 + 5 = 1,780 kcal/day
TDEE at 1.2: 1,780 × 1.2 = 2,136 kcal/day
Revised Harris-Benedict BMR: 88.362 + (13.397 × 80) + (4.799 × 180) − (5.677 × 30) = 88.362 + 1,071.76 + 863.82 − 170.31 = 1,853.63 kcal/day
TDEE at 1.2: 1,853.63 × 1.2 = 2,224.36 kcal/day
Hypothetical Adult B: 25-year-old Female, 62 kg, 165 cm, Moderately Active (1.55)
Mifflin-St Jeor BMR: (10 × 62) + (6.25 × 165) − (5 × 25) − 161 = 620 + 1,031.25 − 125 − 161 = 1,365.25 kcal/day
TDEE at 1.55: 1,365.25 × 1.55 = 2,116.14 kcal/day
Revised Harris-Benedict BMR: 447.593 + (9.247 × 62) + (3.098 × 165) − (4.330 × 25) = 447.593 + 573.314 + 511.17 − 108.25 = 1,423.83 kcal/day
TDEE at 1.55: 1,423.83 × 1.55 = 2,206.94 kcal/day
Hypothetical Adult C: 50-year-old Male, 88 kg, 176 cm, Active (1.725)
Mifflin-St Jeor BMR: (10 × 88) + (6.25 × 176) − (5 × 50) + 5 = 880 + 1,100 − 250 + 5 = 1,735 kcal/day
TDEE at 1.725: 1,735 × 1.725 = 2,992.88 kcal/day
Revised Harris-Benedict BMR: 88.362 + (13.397 × 88) + (4.799 × 176) − (5.677 × 50) = 88.362 + 1,178.936 + 844.624 − 283.85 = 1,828.07 kcal/day
TDEE at 1.725: 1,828.07 × 1.725 = 3,153.42 kcal/day
Formula Limitations
All BMR prediction equations are population-level statistical models, not individual direct measurements. The principal sources of uncertainty in any BMR estimate fall into three categories.
Lean mass estimation uncertainty. Neither the Mifflin-St Jeor nor Harris-Benedict equation includes a direct measurement of lean body mass or fat-free mass. Both use total body weight and height as proxies for lean mass. For individuals with body compositions substantially different from the derivation population averages — individuals at very high or very low proportions of adipose tissue relative to lean mass — prediction error increases. The Frankenfield 2005 review documented higher RMSE values in sub-analyses restricted to higher-BMI subgroups.
Thyroid and endocrine variation. Resting metabolic rate is modulated by circulating thyroid hormone concentrations (thyroxine T4 and triiodothyronine T3), among other endocrine factors. Population-level prediction equations cannot account for individual variation in thyroid status or other endocrine conditions that influence energy expenditure.
Activity factor selection ambiguity. The five-point activity factor scale is intentionally discrete; real human activity patterns exist on a continuous spectrum. Self-selection of an activity factor introduces classification uncertainty that compounds any underlying BMR prediction error. Doubly labeled water studies, the reference method for free-living TDEE measurement, consistently find that self-reported activity classifications exhibit both systematic bias (under-reporting and over-reporting are both documented) and substantial random variance.