Guide · FY2027
Guide to the ICD-10-CM classification
Three short guides to reading the pages of this site, each built on the FY2027 files and quoting the Official Guidelines by section. They describe the classification; they do not tell you which code a record needs.
- How to read an ICD-10-CM codeCategories, subcategories and codes; billable or not; the notes that travel with a code.
- 7th characters and the placeholder XWhich codes take a 7th character, what the characters mean, and when X fills the gap.
- Excludes1 vs Excludes2The two kinds of Excludes notes, where they sit and how many there are.
The full rules are in the ICD-10-CM Official Guidelines for Coding and Reporting FY 2027, published by CMS and NCHS. Adherence to them is required under HIPAA (Guidelines, introduction).