The CHADS₂ score is a straightforward clinical tool that helps estimate the risk of ischemic stroke in patients with non-valvular atrial fibrillation (AF). This tool is recognized for its simplicity and has long served as a foundational risk stratification instrument. It assigns one point each for congestive heart failure, hypertension, age 75 or older, and diabetes mellitus, and two points for a history of stroke or transient ischemic attack (TIA). The total score ranges from 0 to 6.

Annual stroke risk increases as the score rises. Patients scoring 0 have approximately a 1.9 percent yearly risk, while those scoring 1 face a risk of about 2.8 percent; score 2 corresponds to roughly 4.0 percent; score 3 to about 5.9 percent; score 4 reaches around 8.5 percent; score 5 reaches 12.5 percent; and a maximum score of 6 may approach 18.2 percent annual risk. 

Although the CHADS₂ score remains widely used because of its ease, it has limitations. Notably, it may classify patients with genuinely low risk as moderate risk, potentially prompting unnecessary anticoagulation. In contrast, the newer CHA₂DS₂-VASc score refines risk assessment by adding age 65-74, female sex, and vascular disease as risk factors, and by giving two points for age 75+, enhancing the identification of truly low-risk patients