Total Daily Energy Expenditure (TDEE) is the total number of calories your body burns in a day, including your basal metabolic rate (BMR) plus calories burned through physical activity.

How accurate is the Mifflin-St Jeor equation?

The Mifflin-St Jeor equation is considered the most accurate BMR formula for most people, with a margin of error of around ±10%. Individual metabolism varies, so treat the result as a starting point and adjust based on real-world results.

TDEE + Macro Calculator — Daily Calories and Macronutrients

Resting metabolism

Your resting metabolic rate (RMR) — sometimes loosely called BMR — is the energy your body uses when completely at rest. The calculator estimates it using the Mifflin–St Jeor equation (Mifflin et al., 1990), the most accurate of the widely-used RMR formulas when validated against indirect calorimetry in healthy adults:

Men: 10 × weight (kg) + 6.25 × height (cm) − 5 × age (y) + 5
Women: 10 × weight (kg) + 6.25 × height (cm) − 5 × age (y) − 161

Mifflin–St Jeor was calibrated on a modern population. Harris–Benedict, the older formula it largely replaced, was based on 1919 data and overestimates RMR by ~5% in current adults. Mifflin–St Jeor is the formula the Academy of Nutrition and Dietetics recommends for healthy non-obese adults.

Activity multiplier

RMR is multiplied by a Physical Activity Level (PAL) coefficient from the FAO/WHO/UNU 2004 expert report — the international standard for energy expenditure modeling. The result is your total daily energy expenditure (TDEE), the rough caloric intake at which weight is stable.

1.40–1.54: sedentary or light activity (desk job, little structured exercise)
1.55–1.74: moderately active (office work plus 3–4 weekly workouts, or an active job)
1.75–1.99: vigorously active (manual job, or office plus intense daily training)
2.00–2.40: extremely active (heavy labor plus athletics, or competitive endurance training)

The popular five-step ladder (1.2 / 1.375 / 1.55 / 1.725 / 1.9) is a simplified version of the same coefficients.

Macronutrient split

The split between protein, fat, and carbohydrate is structured around the Acceptable Macronutrient Distribution Ranges (AMDR) published by the U.S. Institute of Medicine (IOM, 2005):

Protein: 10–35% of calories. The RDA minimum is 0.8 g/kg for sedentary adults; 1.6–2.2 g/kg is the range commonly recommended for trained populations or weight-loss contexts.
Fat: 20–35% of calories
Carbohydrate: 45–65% of calories

A worked example

A 35-year-old woman, 170 cm, 65 kg, moderately active:

RMR = 10×65 + 6.25×170 − 5×35 − 161 = 1376.5 kcal/day
TDEE at PAL 1.55 = 1376.5 × 1.55 ≈ 2133 kcal/day
At 30% protein: 640 kcal ÷ 4 = 160 g protein/day (~2.5 g/kg)
At 30% fat: 640 kcal ÷ 9 ≈ 71 g/day
At 40% carbs: 853 kcal ÷ 4 ≈ 213 g/day

Limitations

Mifflin–St Jeor is most accurate for healthy adults aged 19–78 with BMI in the normal-to-overweight range. It underestimates RMR for highly muscular individuals (RMR scales with fat-free mass, which the equation captures only indirectly via weight) and can misestimate for older adults with sarcopenia. Estimates have a typical ±10% error band relative to indirect calorimetry — useful for a starting point, not for prescribing a diet to the calorie.

PAL coefficients are population averages. Individual variation is substantial. If estimates from this tool diverge from your observed weight trajectory across two weeks, trust the scale and adjust intake by 100–200 kcal in the appropriate direction.

This is not a clinical or nutritional prescription. Eating disorders, athletic performance optimization, weight management with comorbidities, and any restrictive diet are reasons to work with a registered dietitian — the calculator's outputs are population estimates, not personal advice.

Sources

Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO. (1990). A new predictive equation for resting energy expenditure in healthy individuals . American Journal of Clinical Nutrition 51(2):241–247. Mifflin–St Jeor RMR equation — the BMR formula the calculator uses.
Food and Agriculture Organization of the United Nations, World Health Organization, United Nations University. (2004). Human Energy Requirements: Report of a Joint FAO/WHO/UNU Expert Consultation . FAO Food and Nutrition Technical Report Series 1. Rome. International standard for Physical Activity Level (PAL) coefficients — basis for the sedentary→very-active activity multipliers.
Institute of Medicine (U.S.) Panel on Macronutrients. (2005). Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids . National Academies Press, Washington DC. Acceptable Macronutrient Distribution Ranges (AMDR): 45–65% carbs, 20–35% fat, 10–35% protein — basis for the macro-split defaults.