ICD-10-CM coding guides

The conventions that decide whether a code survives a claim. Each guide quotes the official definition from the ICD-10-CM Tabular List and works through real codes from the FY2027 release.

1. 01

   What “billable” actually means in ICD-10-CM

   Why can't I submit every ICD-10-CM code on a claim?

   Roughly a quarter of ICD-10-CM codes cannot be submitted at all. The rule that decides it, and why a valid code is not the same as a covered one.

2. 02

   Excludes1 vs Excludes2

   What is the difference between an Excludes1 and an Excludes2 note?

   The most misread convention in ICD-10-CM. One forbids reporting two codes together; the other explicitly permits it.

3. 03

   Unspecified codes and denial risk

   When is it acceptable to report an unspecified ICD-10-CM code?

   Unspecified codes are valid and sometimes the only correct choice — but they are also the most common cause of a specificity denial.

4. 04

   7th characters and the placeholder X

   How do 7th characters work in ICD-10-CM, and when do I need a placeholder X?

   Over half of all ICD-10-CM codes carry a 7th character. What each one means, why a code can be invalid without it, and when the placeholder X fills the gap.

5. 05

   Code first, use additional code, and code also

   Which ICD-10-CM code should be sequenced first?

   The etiology/manifestation convention decides sequencing for you. How to recognise a manifestation code and why it can never be listed first.

6. 06

   The ICD-10-CM update cycle

   When do ICD-10-CM codes change, and which code set applies to my claim?

   Codes change on October 1 and sometimes April 1, with no grace period. Why date of service — not date of billing — decides which set applies.

These guides explain the classification’s own conventions. They are not clinical or billing advice, and they do not replace the ICD-10-CM Official Guidelines for Coding and Reporting. Read the disclaimer.