Free CURB-65 Calculator | Pneumonia Severity Score

Understanding the CURB‑65 Severity Score

Pneumonia is a common and potentially severe infection of the lung parenchyma. The CURB‑65 score calculator is a practical tool that uses five clinical variables to stratify patients with community‑acquired pneumonia (CAP) according to mortality risk. By offering an immediate risk estimate, this pneumonia severity calculator helps guide admission decisions and serves as a key part of the CAP severity index.

What is Community‑Acquired Pneumonia?

CAP refers to pneumonia acquired outside of a hospital or long‑term care facility. It is distinguished from hospital‑acquired pneumonia (HAP), which appears after at least 48–72 hours of hospitalization. The differentiation is important because the causative agents differ—CAP is typically caused by different microorganisms than HAP, making the distinction critical for empiric antibiotic selection.

Development of the CURB‑65 Score

The CURB‑65 criteria were introduced in 2003 by a British research group who studied 1068 patients across three countries. Their goal was to create a simple scale that could predict 30‑day mortality and guide hospital admission decisions. The resulting score uses only five items and has since become a standard component of the CAP severity index.

The Five Parameters

Each of the following criteria earns one point, for a total between 0 and 5:

• C – Confusion of new onset (indicates possible CNS involvement)
• U – Blood urea nitrogen > 19 mg/dL (reflects renal perfusion or dehydration)
• R – Respiratory rate ≥ 30 breaths per minute (signifies respiratory distress)
• B – Systolic blood pressure < 90 mmHg or diastolic ≤ 60 mmHg (marker of circulatory compromise)
• 65 – Age ≥ 65 years (established risk factor)

This free CURB‑65 calculator online automatically sums the points as you enter the data.

Mortality Risk Stratification

The following table shows the association between CURB‑65 score and 30‑day mortality from the original validation:

CURB‑65 Score	30‑Day Mortality
0	0.6%
1	2.7%
2	6.8%
3	14.0%
4 or 5	27.8%

Pneumonia Admission Criteria

Based on these mortality estimates, the CURB‑65 score informs admission decisions:

• Score 0–1: Low risk; outpatient treatment is usually safe.
• Score 2: Moderate risk; consider hospital admission depending on comorbidities and home support.
• Score 3–5: High risk; hospital admission is strongly recommended.

When the score is 3 or more, the mortality exceeds 7%, a threshold that typically prompts admission.

Limitations and Important Notes

While the CURB‑65 calculator provides a rapid, evidence‑based assessment, it should not replace a thorough clinical evaluation. Factors such as hypoxemia, comorbid illnesses, and social circumstances must be taken into account. The tool is intended to support decision‑making, not to substitute for professional medical judgment. Always consult a physician for any health concerns.