Centor score calculator

What is the modified Centor (McIsaac) score?

It is a five-item bedside score for a sore throat that estimates how likely the cause is group A streptococcus (GAS), the bacterium behind strep throat. The original Centor score (1981, adults in an emergency room) gave one point each for fever, tonsillar swelling or exudate, tender swollen front neck lymph nodes, and the absence of a cough. McIsaac and colleagues added an age adjustment in a 1998 CMAJ paper because strep is more common in children and less common in older adults: add 1 for ages 3 to 14, 0 for 15 to 44, and subtract 1 for 45 and older.

How likely is strep at each score?

The largest check is a 2012 analysis by Fine, Nizet and Mandl of 206,870 people aged 3 and over who visited US retail clinics for a sore throat and were tested. The share that tested positive for GAS by McIsaac score was 0: 8%, 1: 14%, 2: 23%, 3: 37%, 4: 55%. The smaller 2000 primary-care validation study found 0: 1% (0 to 4%), 1: 10% (6 to 16%), 2: 17% (11 to 25%), 3: 35% (25 to 45%), 4: 51% (40 to 62%). For the classic Centor score in people 15 and older, the retail clinic data show 0: 7%, 1: 12%, 2: 21%, 3: 38%, 4: 57% for scores 0 to 4. Scores of −1 and 5 are folded into 0 and 4, as in these studies. The two data sets differ, which is why this page shows both.

Should a high score mean antibiotics?

No. A score is a probability, not a result: even at the top score, 55% in the retail data and 51% in the primary-care study means that roughly half of the people tested did not have strep. In McIsaac's 2004 JAMA comparison of management strategies, empirical treatment of adults with a score of 3 or 4 was associated with excess unnecessary prescribing; the authors favored selective throat culture and treatment based on positive tests. A positive test, not the score, is what confirms strep.

What does the current IDSA guideline say?

The Infectious Diseases Society of America published a guideline update in October 2025 on group A streptococcal pharyngitis. Its first recommendation is that, in children and adults with sore throat, it suggests using a clinical scoring system to decide who should be tested for GAS (a conditional recommendation, very low certainty of evidence). The aim is to find people with a low probability of strep so that they are not tested needlessly. People at high risk, for example with household exposure to strep, a past episode of rheumatic fever or symptoms suggesting a systemic infection, should be strongly considered for testing whatever the score. It does not apply to children under 3.

Why does the score not apply under age 3?

The score was developed in people 3 and older. The IDSA excludes children under 3 because strep may not show the features the scores use, and the retail clinic study began at age 3. The result on this page is therefore not offered for younger children.

Why is a missing cough a point?

Cough, like a runny nose, is listed among the features that point toward a viral rather than a streptococcal sore throat in a summary of the 2012 IDSA guideline, so its absence adds a point. This page asks only about cough. The score is not made for trouble breathing or swallowing saliva, drooling, a stiff neck or a rash; those need medical care now.

How the points are added

One point each for a history of fever, exudate or swelling of the tonsils, tender swollen lymph nodes at the front of the neck, and no cough. That gives the clinical (Centor) points from 0 to 4. Then adjust for age: +1 for ages 3 to 14, none for 15 to 44, −1 from 45. The result runs from −1 to 5, and the validation studies group −1 with 0 and 5 with 4.

Worked example

An 8-year-old with fever, tonsillar exudate and tender front neck nodes and no cough has 4 Centor points plus 1 for age, a raw total of 5, which the studies fold into 4: 55% tested positive in the retail data. A 28-year-old with fever and no cough scores 2 (23%). A 52-year-old with all four findings has 4 Centor points and loses 1 for age, giving 3 (37%). A 24-year-old with only a cough and none of the other findings scores 0 (8%), which is low but not zero.

Limits of this method

Scores built on small samples do not travel well: the retail clinic data had higher strep rates at a score of 0 (8%) than the 1998 derivation study (3%), and the 2012 authors found that the observed rates fell within the earlier confidence intervals at most scores but not at a McIsaac score of 0. The retail clinic population was two-thirds women with an average age of 34, and it included only patients who were tested for strep. The score also says nothing about complications or about other causes of a sore throat. Use it to focus the question, not to answer it.

Common mistakes

Giving the point for cough when the person does have a cough; the point is for no cough. Applying the age adjustment twice or to a child under 3. Using the classic Centor percentages for a child: the classic score was studied in adults, and the McIsaac version covers 3 and older. And treating the score as a replacement for a throat swab: a rapid test or culture is how strep is confirmed.

Sources: Centor RM, Witherspoon JM, Dalton HP, Brody CE, Link K, “The diagnosis of strep throat in adults in the emergency room,” Med Decis Making 1981;1:239–246; 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; McIsaac WJ, Goel V, To T, Low DE, “The validity of a sore throat score in family practice,” CMAJ 2000;163:811–815; McIsaac WJ, Kellner JD, Aufricht P, Vanjaka A, Low DE, “Empirical validation of guidelines for the management of pharyngitis in children and adults,” JAMA 2004;291:1587–1595; Fine AM, Nizet V, Mandl KD, “Large-scale validation of the Centor and McIsaac scores to predict group A streptococcal pharyngitis,” Arch Intern Med 2012;172:847–852 (Table 3); Infectious Diseases Society of America, “Group A Streptococcal (GAS) Pharyngitis: Risk Assessment Using Clinical Scoring Systems in Children and Adults” (guideline update, October 2025). Related: BMI calculator, Glasgow Coma Scale, QTc calculator.

For general information only — not medical advice, and not a tool for patient care decisions. Talk with a doctor or pharmacist about a sore throat that is severe or lasts. How we check our calculators.