Calorie & Protein Requirements Calculator

Calorie & Protein Calculator

Age (years)

Biological Sex

Height (cm)

Weight (kg)

Activity Level

Stress Factor

Protein Requirement Context

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BMR — Mifflin-St Jeor (kcal/day)

Formulas

Mifflin-St Jeor (preferred):
Male: BMR = (10 × Wt kg) + (6.25 × Ht cm) − (5 × Age) + 5
Female: BMR = (10 × Wt kg) + (6.25 × Ht cm) − (5 × Age) − 161

Harris-Benedict (original, 1919):
Male: BMR = 66.5 + (13.75 × Wt) + (5.003 × Ht) − (6.775 × Age)
Female: BMR = 655.1 + (9.563 × Wt) + (1.850 × Ht) − (4.676 × Age)

TDEE = MSJ BMR × Activity Factor
Stress-Adjusted Calories = TDEE × Stress Factor

Activity & Stress Factors

Activity Level	Factor	Description
Sedentary / Bed rest	1.20	Little or no physical activity
Lightly active	1.375	Light exercise 1–3 days/week
Moderately active	1.55	Moderate exercise 3–5 days/week
Very active	1.725	Hard exercise 6–7 days/week
Critically ill	1.20	ICU / ventilated — apply stress factor separately

Stress Factor	Value	Clinical Scenario
No stress	1.00	Normal, healthy or minor illness
Minor surgery	1.10	Minor elective procedures
Moderate stress	1.25	Moderate trauma, infection, GI surgery
Major surgery / burns <30%	1.40	Major abdominal surgery, major trauma, burns <30% BSA
Severe burns >30%	1.75	Extensive burns >30% BSA, hypermetabolic states

Protein Requirements

Clinical Context	Requirement	Examples
Normal	0.8–1.0 g/kg/day	Healthy adults, minor illness, elective patients
Post-operative	1.2–1.5 g/kg/day	Elective and emergency surgery, moderate stress
Critical illness	1.5–2.0 g/kg/day	ICU, sepsis, multi-organ failure, major trauma
Burns	2.0–2.5 g/kg/day	Major burns >20% BSA, hypermetabolic states

Protein targets should be based on ideal or adjusted body weight in obese patients, not actual weight, to avoid overfeeding.

Clinical Application

Formula preference: The Mifflin-St Jeor equation is more accurate for most individuals (within 10% of measured REE in approximately 82% of subjects) and is preferred over the original Harris-Benedict equation, which tends to overestimate BMR by 5–15%.
Critical care nutrition: For ventilated or critically ill patients, indirect calorimetry is the gold standard for estimating energy needs. When unavailable, predictive equations with stress factors are used. Most ESPEN/ASPEN guidelines recommend 25–30 kcal/kg/day as a practical target in critical illness.
Post-operative feeding: ERAS protocols support early enteral nutrition within 24 hours of major gastrointestinal surgery. Protein delivery is the most important nutritional target in the perioperative period.
Obesity: In obese patients (BMI >30), energy requirements should be calculated using adjusted or ideal body weight to avoid overfeeding. Hypocaloric high-protein feeding (60–70% of estimated TDEE, protein 1.5–2 g/kg IBW) may reduce complications in critically ill obese patients.
Burns: The Curreri formula (25 kcal/kg/day + 40 kcal/% BSA burned) is an alternative for major burns; caloric requirements can be 40–100% above basal in extensive burns.

References

Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 1990;51(2):241–247.
Harris JA, Benedict FG. A biometric study of human basal metabolism. Proc Natl Acad Sci USA. 1918;4(12):370–373.
Singer P, Blaser AR, Berger MM, et al. ESPEN guideline on clinical nutrition in the intensive care unit. Clin Nutr. 2019;38(1):48–79.
McClave SA, Taylor BE, Martindale RG, et al. Guidelines for the Provision and Assessment of Nutrition Support Therapy in the Adult Critically Ill Patient: SCCM and ASPEN. JPEN. 2016;40(2):159–211.

Calorie & Protein Requirements

Formulas

Activity & Stress Factors

Protein Requirements

Clinical Application

References

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