ICD-10-CM codes are updated annually, with new codes added, existing codes revised, and some codes deleted. Using codes from the wrong year can result in claim denials, compliance issues, and audit findings. Understanding the complete ICD-10 coding guidelines — including rules like Code First, Excludes1 vs Excludes2, and specificity requirements — is essential for applying year-specific rules correctly.
Understanding ICD-10 Fiscal Years
ICD-10-CM updates take effect October 1 each year, aligning with the federal fiscal year:
- FY2026: October 1, 2025 - September 30, 2026 — View 2026 updates
- FY2025: October 1, 2024 - September 30, 2025 — View 2025 updates
- FY2024: October 1, 2023 - September 30, 2024
Key Rule
Claims must use codes valid for the date of service, not the date of submission. A service on September 30 uses the prior year's codes; a service on October 1 uses the new year's codes.
Common Year-Related Issues
Deleted Codes
Codes that existed in a prior year may be deleted. Using a deleted code for a current-year service results in automatic rejection.
New Codes
New codes added in the current year are invalid for services before October 1. Using them for prior dates will cause rejections.
Revised Codes
Some codes are revised with changes to descriptions, Excludes notes, or Code First instructions. Using the wrong year's guidelines can result in incorrect coding.
Validate Against the Correct Year
Our Code Auditor supports 2024, 2025, and 2026 guidelines.
Impact of Year Mismatches
Claim Denials
Payer systems validate codes against the date of service. Invalid codes result in automatic rejection requiring correction and resubmission.
Audit Findings
Auditors review coding against the guidelines in effect for the service date. Using the wrong year's rules can result in audit findings even if the code itself is valid.
Quality Measure Impact
Quality measures may require specific codes that change year to year. Using incorrect codes can affect quality scores.
Best Practices
- Update coding references immediately when new codes are released
- Train coders on significant changes each October
- Use validation tools that support multiple guideline years
- Review annual updates before they take effect
- Maintain access to prior year code sets for legacy claims
Transition Periods
The weeks around October 1 require special attention. Claims for September services use the prior year's codes, while October services use the new codes. Many organizations process both simultaneously, increasing error risk.