CURB-65 Score Calculator (Community-Acquired Pneumonia Severity)

Background.

CURB-65 grades the severity of community-acquired pneumonia in an adult presenting to hospital, and it supports a site-of-care and monitoring decision. It assumes the diagnosis has already been made: nothing on this page diagnoses pneumonia, and a low score in a patient who has not been assessed clinically means nothing at all. It is a clinical decision aid for clinicians, not a diagnosis, and it does not select an antibiotic.

The name is the criteria. Confusion, Urea above 7 mmol/L, Respiratory rate of 30 or more, low Blood pressure, and age 65 or over. Each scores one point, for a total between 0 and 5. Confusion has a specific operational definition — an abbreviated Mental Test score of 8 or less, or new disorientation in person, place or time — and not simply an impression that the patient seems muddled. Low blood pressure is a composite: it fires when the systolic is below 90 mmHg or the diastolic is 60 mmHg or less, and it still contributes only one point when both are true.

The five thresholds are worded with three different strictnesses, and this is what most implementations get wrong. Urea must be strictly above 7 mmol/L, so a urea of exactly 7.0 does not score. Respiratory rate scores at 30 or more, so 30 does score. Systolic pressure must be strictly below 90, so a systolic of exactly 90 does not score. Diastolic scores at 60 or less, so 60 does score. Age scores at 65 or more, so a 65th birthday does score. This calculator implements each comparison exactly as the source words it, and shows the urea point and the blood-pressure point as separate outputs so you can check them against your own reading.

Units are the other classic trap. The criterion is a serum urea of more than 7 mmol/L. If your laboratory reports blood urea nitrogen in mg/dL, the exact equivalent is 19.61 mg/dL, because one mmol/L of urea corresponds to 2.8014 mg/dL of urea nitrogen. Published conversions round that to 19 or to 20; the difference is small but it sits directly on a threshold, so this page takes urea in mmol/L — the unit the source uses — and prints the exact mg/dL equivalent on the field rather than offering a toggle that would hide which rounding was applied.

This calculator deliberately does not print a mortality percentage, and the reason is worth stating plainly. The derivation paper's own abstract reports 30-day mortality as 0.7 percent at a score of 0, 3.2 percent at 1, 3 percent at 2, 17 percent at 3, 41.5 percent at 4 and 57 percent at 5. That series is not monotonic: the figure printed for a score of 2 is lower than the figure printed for a score of 1, which cannot be right. The value most often re-quoted elsewhere for a score of 2 is 13 percent, but that is a secondary reading, and the paper's own tables could not be retrieved to settle it. Rather than pick one silently, this page reports the score and the risk group from NICE — under 3 percent for 0 to 1, 3 to 15 percent for 2, and over 15 percent for 3 to 5 — which is internally consistent and comes from a current issuing body.

Scope limits matter. CURB-65 was derived and validated in adults presenting to hospital with community-acquired pneumonia in the United Kingdom, New Zealand and the Netherlands, across 1,068 patients with an overall 30-day mortality of 9 percent. It is not validated for hospital-acquired or ventilator-associated pneumonia, for significantly immunosuppressed patients, or for children. It measures severity at one moment on presentation, and a patient who deteriorates over the next twelve hours needs rescoring and reassessment, not a note recording the number they arrived with.

Finally, a score is not a decision. A low CURB-65 in a patient who lives alone, cannot take oral medication, has an oxygen saturation of 88 percent, or has decompensated comorbidity is not an argument for discharge. Guidelines have always framed CURB-65 as one input alongside clinical judgement, social circumstances and oxygenation — never as the whole assessment.

What is curb-65 score calculator?

CURB-65 is a five-point severity score for community-acquired pneumonia, derived by Lim and colleagues and published in Thorax in 2003. It was built from an international dataset of 1,068 patients across the United Kingdom, New Zealand and the Netherlands, with an overall 30-day mortality of 9 percent, and it was designed to be calculable at the bedside from observations and a single blood test.

The five components are confusion, urea above 7 mmol/L, respiratory rate of 30 or more, low blood pressure (systolic below 90 or diastolic 60 or less), and age 65 or over. Each is worth one point.

Its practical role is to sort patients into groups with markedly different mortality so that the intensity of care can be matched to risk. NICE stratifies the score into low risk at 0 to 1, intermediate risk at 2, and high risk at 3 to 5, with mortality bands of under 3 percent, 3 to 15 percent and over 15 percent respectively.

What it is not: a diagnostic test for pneumonia, an antibiotic-selection tool, a measure of oxygenation, or a substitute for assessing whether a particular patient can safely be managed at home. Other severity instruments exist, notably the Pneumonia Severity Index of Fine and colleagues, which uses around twenty variables and is more laborious but stratifies low-risk patients more finely.

How to use this calculator.

1. 01Confirm a diagnosis of community-acquired pneumonia first. CURB-65 grades severity; it does not diagnose.
2. 02Answer the confusion item using the operational definition — an abbreviated Mental Test score of 8 or less, or new disorientation in person, place or time — not a general impression.
3. 03Enter serum urea in mmol/L. If your laboratory reports BUN in mg/dL, divide by 2.8014 first; the threshold of 7 mmol/L is 19.61 mg/dL.
4. 04Enter the respiratory rate you counted, not the one recorded from a monitor trace, and the blood pressure at presentation.
5. 05Enter both systolic and diastolic pressures. The blood-pressure criterion is a composite and can fire on either limb, but it contributes at most one point.
6. 06Read the total and the risk group together, and check the urea and blood-pressure points against your own reading of the values.
7. 07Treat the result as one input alongside oxygenation, comorbidity, social circumstances and clinical judgement — a low score does not by itself justify discharge.
8. 08Rescore if the patient's observations change. The score describes the moment it was taken.

The formula.

CURB-65 adds one point for each of five criteria, giving a total from 0 to 5. Confusion — defined as an abbreviated Mental Test score of 8 or less, or new disorientation in person, place or time — adds 1. Serum urea strictly above 7 mmol/L adds 1. A respiratory rate of 30 breaths per minute or more adds 1. Low blood pressure, meaning a systolic below 90 mmHg or a diastolic of 60 mmHg or less, adds 1. Age of 65 years or more adds 1.

Rounding stage: there is none. All five weights are 1 and the total is an exact integer sum. Every entered value is compared against its threshold exactly as entered; nothing is rounded before a comparison, so a urea of 7.05 mmol/L scores and a urea of 7.00 does not.

The comparisons are not uniform, and reproducing them casually is the most common implementation error. Urea uses a strict inequality — above 7, so 7.0 does not fire. Respiratory rate uses an inclusive one — 30 or more, so 30 does fire. Systolic pressure uses a strict inequality — below 90, so 90 does not fire. Diastolic pressure uses an inclusive one — 60 or less, so 60 does fire. Age uses an inclusive one — 65 or more, so 65 does fire. This calculator implements each as written, and its tests check the value immediately below, at, and immediately above every one of those five thresholds.

The blood-pressure criterion is the only composite. It has two limbs, systolic and diastolic, and it fires if either is met. It contributes one point whether one limb is met or both, which is why the calculator reports the blood-pressure point as its own output — a patient with a pressure of 84/50 scores the same single point as a patient with 118/58.

Interpretation uses the NICE strata: 0 to 1 is low risk with a stated mortality of under 3 percent, 2 is intermediate risk with 3 to 15 percent, and 3 to 5 is high risk with over 15 percent. No individual mortality percentage is computed, for the reason set out in the introduction.

Worked through the example on this page: confusion present adds 1, urea 9.4 mmol/L is above 7 and adds 1, a respiratory rate of 24 is below 30 and adds nothing, a blood pressure of 128/76 meets neither limb and adds nothing, and an age of 78 is 65 or more and adds 1. The total is 1 + 1 + 1 = 3, which is the high-risk group.

A worked example.

Frequently asked questions.

References& sources.

1. [1]Lim WS, van der Eerden MM, Laing R, et al. Defining community acquired pneumonia severity on presentation to hospital: an international derivation and validation study. Thorax. 2003;58(5):377–382. Derivation of CURB-65; n = 1,068; overall 30-day mortality 9%; the per-score mortality series quoted (and questioned) on this page. (Abstract retrieved verbatim 2026-07-29.)
2. [2]Lim WS, et al. Thorax 2003;58:377–382 — free full-text copy in PubMed Central. Consulted 2026-07-29 for the paper's own tables; the article body could not be extracted by automated retrieval, which is why the score-2 mortality discrepancy is reported on this page rather than resolved.
3. [3]National Institute for Health and Care Excellence. Pneumonia in adults: diagnosis and management. NICE clinical guideline CG191 (2014, updated 2019). Source of the operational confusion definition (abbreviated Mental Test score 8 or less, or new disorientation in person, place or time), of all five thresholds, and of the risk strata used here: 0–1 low (under 3% mortality), 2 intermediate (3–15%), 3–5 high (over 15%). (nice.org.uk blocks automated retrieval; recommendation text consulted 2026-07-29.)
4. [4]National Institute for Health and Care Excellence. Pneumonia: diagnosis and management. NICE guideline NG250, published 2 September 2025 — supersedes CG191. Listed so readers can check current UK practice. Its content could not be retrieved by automated fetch, and no claim about what it says is made on this page. (Consulted 2026-07-29.)
5. [5]Fine MJ, Auble TE, Yealy DM, et al. A prediction rule to identify low-risk patients with community-acquired pneumonia. N Engl J Med. 1997;336(4):243–250. The Pneumonia Severity Index — cited only to establish that a more detailed alternative exists. (Bibliographic; consulted 2026-07-29.)
6. [6]Metlay JP, Waterer GW, Long AC, et al. Diagnosis and Treatment of Adults with Community-acquired Pneumonia. An Official ATS/IDSA Clinical Practice Guideline. Am J Respir Crit Care Med. 2019;200(7):e45–e67. Cited to establish that a separate US guideline covers the site-of-care decision. Full text could not be retrieved, so no claim is made here about which severity tool it prefers. (Abstract consulted 2026-07-29.)