What is the difference between Harris-Benedict and Mifflin-St Jeor?

Both estimate basal metabolic rate from sex, weight, height, and age. Mifflin-St Jeor (1990) is generally considered more accurate in modern populations, while the revised Harris-Benedict equation is the long-established reference. The tool shows both so you can compare.

How is total energy expenditure calculated?

Total daily energy expenditure equals BMR multiplied by an activity factor and a stress factor. The activity factor reflects mobility, while the stress factor accounts for the increased metabolic demand of illness, surgery, sepsis, or burns.

How much protein should a patient receive?

Protein needs are weight-based, typically 0.8 to 2.0 grams per kilogram per day depending on clinical state. Critically ill or catabolic patients often need 1.2 to 2.0 g/kg/day, which the tool estimates from the selected protein factor.

Should I use actual or adjusted body weight?

For patients within a healthy weight range, use actual body weight. For obese patients many units use an adjusted body weight to avoid overfeeding. Enter the weight your protocol specifies; the equations apply it directly.

Nutritional Requirements Calculator (Harris-Benedict / Mifflin)

Clinical energy and protein requirements

Estimating a patient’s energy and protein needs is the foundation of clinical nutrition support, whether enteral, parenteral, or oral. This calculator computes basal metabolic rate (BMR) with two established equations, scales it to total daily energy expenditure (TDEE) using activity and stress factors, and derives a weight-based protein target.

The two BMR equations

Mifflin-St Jeor (1990) — generally preferred for current populations

Men:   BMR = 10 × weight + 6.25 × height − 5 × age + 5
Women: BMR = 10 × weight + 6.25 × height − 5 × age − 161
(weight in kg, height in cm, age in years)

The Mifflin-St Jeor equation was derived from a 1990 study of 498 men and women and is broadly considered more accurate for modern populations than the original Harris-Benedict equation, which was published in 1919 and derived from a smaller dataset.

Revised Harris-Benedict (1984)

Men:   BMR = 88.362 + 13.397 × weight + 4.799 × height − 5.677 × age
Women: BMR = 447.593 + 9.247 × weight + 3.098 × height − 4.330 × age

The Harris-Benedict equation remains widely used in clinical practice, particularly in protocols and clinical literature that reference it as a standard. Showing both equations allows comparison and helps match your local protocol’s chosen reference.

Scaling BMR to TDEE: activity and stress factors

Basal metabolic rate represents energy needs at complete rest. Real patients need more. Two multipliers are applied:

TDEE = BMR × activity factor × stress factor

Activity factor reflects mobility:

Factor	Clinical situation
1.0	Bedridden, sedated ICU patient
1.1–1.2	Bed-bound but awake
1.2–1.3	Ambulatory, low mobility
1.5–1.75	Active rehabilitation

Stress factor reflects the metabolic response to illness:

Factor	Condition
1.0	Uncomplicated surgical recovery
1.1–1.2	Moderate illness, minor infection
1.3–1.5	Major surgery, sepsis, severe pneumonia
1.5–2.0	Burns, polytrauma, severe catabolism

Stress factors increase requirements because inflammation, fever, wound healing, and catabolism all consume energy beyond the basal level. In practice, combined multipliers rarely exceed 2.0 times BMR, and overfeeding can be as harmful as underfeeding in ICU patients.

Protein targets

Protein needs are estimated separately from energy:

protein g/day = weight (kg) × protein factor (g/kg/day)

Typical protein factors:

Condition	Protein factor
Healthy, low activity	0.8 g/kg/day
Post-operative, moderate illness	1.0–1.2 g/kg/day
Critical illness, sepsis	1.2–2.0 g/kg/day
Burns, severe trauma	1.5–2.0 g/kg/day or higher

Higher protein intake preserves lean muscle mass and supports immune function during catabolism. Many ICU protocols now target 1.2–1.5 g/kg/day as a reasonable starting point for critically ill patients.

Practical notes for clinical use

Weight selection: use actual body weight for patients within normal range. For obese patients, many units apply an adjusted body weight to avoid overfeeding: ABW = ideal body weight + 0.25 × (actual − ideal). Enter the weight your protocol specifies.
Reassess frequently: metabolic needs change as illness severity changes. A septic patient may need 1.5× BMR on day 1 and approach normal by day 5.
Indirect calorimetry: when available, measured resting metabolic rate from indirect calorimetry is more accurate than any predictive equation, particularly for extreme body compositions and critically ill patients.
This tool provides estimates, not personalised clinical advice. Confirm all nutrition prescriptions with a registered dietitian and against your institution’s protocol.