Curb 65 Score Calculator
Assess pneumonia severity and determine inpatient vs outpatient treatment using CURB-65. Enter values for instant results with step-by-step formulas.
Calculator
Adjust values & calculateRecommended Disposition
Outpatient treatment likely appropriate. Consider oral antibiotics and follow-up in 48-72 hours.
CURB-65 Severity Scale
Formula
Each criterion adds 1 point. Total score ranges from 0 to 5. Score 0-1: Low risk (~0.6-2.7% mortality), consider outpatient. Score 2: Moderate risk (~6.8%), consider admission. Score 3-5: High risk (~14-57%), hospital/ICU admission.
Last reviewed: January 2026
Worked Examples
Example 1: Low Severity Pneumonia
Example 2: High Severity Pneumonia
Background & Theory
The Curb-65 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 Curb-65 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
CURB-65 = Confusion(1) + Urea>7(1) + RR≥30(1) + BP low(1) + Age≥65(1)
Each criterion adds 1 point. Total score ranges from 0 to 5. Score 0-1: Low risk (~0.6-2.7% mortality), consider outpatient. Score 2: Moderate risk (~6.8%), consider admission. Score 3-5: High risk (~14-57%), hospital/ICU admission.
Worked Examples
Example 1: Low Severity Pneumonia
Problem: 45-year-old with productive cough, RR 22, BP 130/80, oriented, normal urea.
Solution: Confusion: No (0)\nUrea >7: No (0)\nRR ≥30: No (0)\nBP low: No (0)\nAge ≥65: No (0)\nTotal CURB-65 = 0\n30-day mortality: 0.6%
Result: CURB-65 0 — Low Severity, outpatient treatment appropriate
Example 2: High Severity Pneumonia
Problem: 78-year-old confused patient with RR 34, BP 80/50, urea 12 mmol/L.
Solution: Confusion: +1\nUrea >7: +1\nRR ≥30: +1\nBP low: +1\nAge ≥65: +1\nTotal CURB-65 = 5\n30-day mortality: 57%
Result: CURB-65 5 — High Severity, ICU admission required
Frequently Asked Questions
What is the CURB-65 score?
CURB-65 is a clinical prediction tool for assessing the severity of community-acquired pneumonia (CAP) and guiding site-of-care decisions. The acronym stands for: Confusion, Urea >7 mmol/L, Respiratory rate ≥30, Blood pressure (systolic <90 or diastolic ≤60), and age ≥65. Each criterion scores 1 point, giving a total range of 0-5. It was developed by the British Thoracic Society and is recommended by multiple international guidelines.
How does CURB-65 guide treatment decisions?
Score 0-1: Low risk, consider outpatient treatment with oral antibiotics. Score 2: Moderate risk, consider short inpatient stay or hospital-supervised outpatient care. Score 3-5: High risk, hospital admission required. Scores 4-5 strongly suggest ICU admission. These recommendations should be combined with clinical judgment, comorbidities, and social factors.
What is the difference between CURB-65 and CRB-65?
CRB-65 omits the Urea criterion, making it suitable for use in primary care and outpatient settings where blood tests may not be immediately available. It uses only Confusion, Respiratory rate, Blood pressure, and age ≥65. Scoring: 0 = very low risk (outpatient), 1-2 = increased risk (consider hospital referral), 3-4 = high risk (urgent hospital admission).
What are the limitations of CURB-65?
Limitations include: 1) Does not account for comorbidities (COPD, diabetes, immunosuppression). 2) May underestimate severity in younger patients with severe sepsis. 3) Does not incorporate radiographic findings or oxygenation status. 4) Less validated in healthcare-associated and hospital-acquired pneumonia. 5) Should be supplemented with clinical judgment regarding social factors, ability to take oral medications, and follow-up availability.
Can I use the results for professional or academic purposes?
You may use the results for reference and educational purposes. For professional reports, academic papers, or critical decisions, we recommend verifying outputs against peer-reviewed sources or consulting a qualified expert in the relevant field.
Does Curb 65 Score Calculator work offline?
Once the page is loaded, the calculation logic runs entirely in your browser. If you have already opened the page, most calculators will continue to work even if your internet connection is lost, since no server requests are needed for computation.
References
Reviewed by Rahul Singh, Health & Wellness Specialist · Editorial policy