Apache Ii Score Calculator
Calculate the APACHE II severity of disease score for ICU patients. Enter values for instant results with step-by-step formulas.
Calculator
Adjust values & calculateAPACHE II Mortality Scale
Formula
12 physiologic variables are scored based on deviation from normal (worst values in first 24 hours of ICU admission). Age adds 0-6 points. Chronic health adds 0-5 points. Total ranges from 0 to 71, though scores above 40 are rare. Higher scores indicate greater disease severity and predicted mortality.
Last reviewed: January 2026
Worked Examples
Example 1: Low Severity ICU Admission
Example 2: High Severity Septic Shock
Background & Theory
The APACHE II Score Calculator applies the following established principles and formulas. Health and medicine calculators are grounded in validated physiological measurement methods established through decades of clinical research. Body Mass Index, or BMI, is calculated by dividing weight in kilograms by height in meters squared (kg/m²), a formula originating from Adolphe Quetelet's 19th-century statistical work and later codified by the WHO into standard classifications: underweight below 18.5, normal weight 18.5 to 24.9, overweight 25 to 29.9, and obese at 30 and above. Basal Metabolic Rate quantifies the minimum energy required to sustain life at rest. The Mifflin-St Jeor equation, published in 1990 and widely regarded as the most accurate for most adults, calculates BMR as (10 × weight in kg) + (6.25 × height in cm) − (5 × age) ± sex adjustment. The older Harris-Benedict equations, revised in 1984 by Roza and Shizgal, remain in common use. Total Daily Energy Expenditure is derived by multiplying BMR by a physical activity factor ranging from 1.2 for sedentary individuals to 1.9 for extremely active ones, following the methodology validated by doubly labeled water studies. Body fat percentage can be estimated without laboratory equipment using the U.S. Navy circumference method, which uses neck, waist, and hip measurements, or via BMI-derived equations adjusted for age and sex. The Jackson-Pollock skinfold method offers higher precision with calipers. Blood pressure classification, according to the American College of Cardiology and the 2017 ACC/AHA guidelines, defines normal as below 120/80 mmHg, elevated as 120 to 129 systolic, and hypertension stage 1 as 130 to 139 systolic or 80 to 89 diastolic. Target heart rate zones for aerobic exercise are derived from maximum heart rate estimates, most commonly using the formula 220 minus age in years, with moderate-intensity training typically defined as 50 to 70 percent of maximum heart rate and vigorous intensity at 70 to 85 percent, consistent with CDC and American Heart Association guidelines. These thresholds guide safe and effective cardiovascular conditioning.
History
The history behind the APACHE II Score Calculator traces back through the following developments. The history of health measurement stretches back to ancient Greece, where Hippocrates around 400 BCE laid the foundation for observational medicine by systematically recording patient symptoms, diet, and environment. His humoral theory, though scientifically superseded, established the principle that the body operates as an interconnected system subject to measurable imbalance. The transformation toward modern medicine accelerated in the 19th century. Louis Pasteur and Robert Koch developed germ theory in the 1860s and 1870s, identifying microorganisms as disease agents and enabling targeted interventions. Florence Nightingale, working during the Crimean War in the 1850s, introduced statistical analysis to nursing practice, demonstrating through data visualization that sanitation reduced mortality. Her work is foundational to evidence-based health measurement. The discovery of vitamins in the early 20th century, beginning with Casimir Funk's coinage of the term in 1912 and culminating in the isolation of vitamins A through K, created the field of nutritional science and gave rise to dietary reference intake frameworks. The World Health Organization, founded in 1948, subsequently established global standards for health metrics, disease classification through the International Classification of Diseases, and recommended daily allowances. The BMI as a clinical screening tool gained traction in the 1970s through Ancel Keys' large-scale epidemiological work, which validated Quetelet's index as a population-level obesity indicator. Through the 1980s and 1990s, the Framingham Heart Study produced landmark data linking cholesterol, blood pressure, and lifestyle factors to cardiovascular disease risk, directly shaping the numeric thresholds still used in health calculators. The evidence-based medicine movement, formalized by Gordon Guyatt and colleagues at McMaster University in the early 1990s, demanded that all health recommendations derive from systematically graded clinical evidence. The digital health era beginning in the 2000s brought these formulas to consumer devices, wearable sensors, and smartphone applications, expanding access to health self-monitoring on a global scale and enabling population-level data collection that continues to refine clinical reference ranges.
Frequently Asked Questions
Formula
APACHE II = Acute Physiology Score (0-60) + Age Points (0-6) + Chronic Health Points (0-5)
12 physiologic variables are scored based on deviation from normal (worst values in first 24 hours of ICU admission). Age adds 0-6 points. Chronic health adds 0-5 points. Total ranges from 0 to 71, though scores above 40 are rare. Higher scores indicate greater disease severity and predicted mortality.
Worked Examples
Example 1: Low Severity ICU Admission
Problem: 55-year-old post-elective surgery, mild tachycardia, all labs normal, alert.
Solution: Heart Rate: 2 (110-139)\nAge: 3 (55-64)\nChronic: 0\nAll others: 0\nTotal APACHE II = 5\nPredicted mortality: ~8%
Result: APACHE II 5 — Low-Moderate severity
Example 2: High Severity Septic Shock
Problem: 72-year-old with septic shock, temp 40.5°C, MAP 45, HR 155, acute renal failure, GCS 8.
Solution: Temperature: 3\nMAP: 4\nHR: 3\nCreatinine: 4 (acute)\nGCS points: 9\nAge: 5\nChronic: 5\nTotal APACHE II = 33\nPredicted mortality: ~73%
Result: APACHE II 33 — Critical severity, very high predicted mortality
Frequently Asked Questions
What is the APACHE II score?
APACHE II (Acute Physiology and Chronic Health Evaluation II) is a severity-of-disease classification system used in ICUs worldwide. Introduced in 1985 by Knaus et al., it uses 12 physiologic variables, age, and chronic health status to generate a score from 0-71. Higher scores indicate more severe disease and higher predicted mortality. It is calculated within 24 hours of ICU admission using the worst values.
How is APACHE II mortality predicted?
APACHE II provides an estimated in-hospital mortality based on the total score. Approximate mortality by score range: 0-4: ~4%, 5-9: ~8%, 10-14: ~15%, 15-19: ~25%, 20-24: ~40%, 25-29: ~55%, 30-34: ~73%, ≥35: ~85%. The actual mortality equation also incorporates the primary diagnosis category, but the score alone provides a reasonable estimate.
What are the limitations of APACHE II?
Limitations include: 1) Developed in the 1980s, may not reflect modern ICU practices. 2) Uses worst values in 24 hours, which may be affected by treatment. 3) Does not account for lead-time bias. 4) Chronic health assessment is subjective. 5) Newer versions (APACHE III, IV) exist but are proprietary. 6) Should not be used for individual patient prognosis or withdrawal of care decisions.
When should APACHE II values be collected?
APACHE II should be calculated using the worst (most abnormal) values from the first 24 hours after ICU admission. If a variable is not measured, it is assumed to be normal (score 0). The GCS component should use the pre-sedation or pre-intubation value when possible. Serial calculations are not standard but may be used to track disease progression.
How accurate are the results from Apache Ii Score Calculator?
All calculations use established mathematical formulas and are performed with high-precision arithmetic. Results are accurate to the precision shown. For critical decisions in finance, medicine, or engineering, always verify results with a qualified professional.
How do I get the most accurate result?
Enter values as precisely as possible using the correct units for each field. Check that you have selected the right unit (e.g. kilograms vs pounds, meters vs feet) before calculating. Rounding inputs early can reduce output precision.
References
Reviewed by Rahul Singh, Health & Wellness Specialist · Editorial policy