Centor / McIsaac Score Calculator (Strep Pharyngitis)
The Centor score, with McIsaac’s age modification, estimates the probability of group A streptococcal pharyngitis from four clinical criteria — tonsillar exudate, tender anterior cervical nodes, fever by history, and absence of cough — plus an age adjustment, to guide rapid-strep testing and antibiotics.
Quick answer
The Centor score adds one point each for tonsillar exudate, tender anterior cervical nodes, fever by history, and absence of cough. McIsaac’s modification then adds 1 point for ages 3–14 and subtracts 1 for ages 45 and over, giving a total of −1 to 5 that estimates the probability of group A streptococcal pharyngitis.
Centor criteria
McIsaac age modifier
+1 point for ages 3–14, 0 for 15–44, −1 for 45 and over.
How to use the Centor / McIsaac calculator
- 1Tick the four Centor criteria. Tick tonsillar exudate or swelling, tender or swollen anterior cervical lymph nodes, a history of fever (over 38 °C), and the absence of cough.
- 2Enter the age. Enter the patient’s age; the tool applies the McIsaac modifier (+1 for 3–14 years, −1 for 45 years and over).
- 3Read the score and probability. The tool shows the modified score and the associated strep probability band, to guide rapid antigen testing or treatment with a clinician.
Medical disclaimer: This is general health information, not medical advice. It does not diagnose or treat any condition, and the results are estimates based on public reference formulas. Always consult a qualified doctor about your individual health. If you think you may have a medical emergency, contact your local emergency services immediately.
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Book a consultationFrequently asked questions
What Centor score needs a strep test?⌄
Broadly, a modified (McIsaac) score of 2–3 supports a rapid strep test, and 4 or more supports testing and/or empirical treatment per local guidance, while a score of 0–1 has a low enough probability that testing and antibiotics are usually not needed. A clinician decides.
What is the difference between the Centor and McIsaac scores?⌄
The Centor score uses four clinical criteria; the McIsaac modification adds an age adjustment (+1 for children 3–14, −1 for adults 45 and over) because strep is more common in children and less common in older adults. This tool reports the modified McIsaac total.
Why does the absence of cough score a point?⌄
A cough points towards a viral cause rather than streptococcal pharyngitis, so its absence makes strep more likely and therefore scores one point in the model.
Is my data stored?⌄
No. The calculator runs entirely in your browser; nothing you enter is sent to a server.
Sources & validation
This calculator reproduces the published Centor / McIsaac score, validated for probability of group A streptococcal pharyngitis and testing/treatment triage in sore throat.
- Centor RM, Witherspoon JM, Dalton HP, et al. The diagnosis of strep throat in adults in the emergency room (Med Decis Making 1981;1:239-246) — the original 4-criterion Centor score — verified 2026-06-18
- McIsaac WJ, White D, Tannenbaum D, Low DE. A clinical score to reduce unnecessary antibiotic use in patients with sore throat (CMAJ 1998;158:75-83) — adds the age modifier (+1 for 3–14y, −1 for ≥45y) and strep probabilities — verified 2026-06-18
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