The ICD-10-CM code set is updated annually every October 1 by CMS and the CDC. Each update cycle introduces new codes, revises existing codes, and makes existing codes invalid. For 2026, healthcare organisations need to be aware of the changes that took effect October 1, 2025 and prepare their coding teams, training software, and AI coding platforms accordingly.
ICD-10-CM 2026: Key Updates and What They Mean for Coders
The FY2026 ICD-10-CM update (effective October 1, 2025) introduced over 500 new codes, revised hundreds of existing codes, and made over 200 codes invalid. Key areas of expansion included mental health and behavioural diagnoses, social determinants of health (SDOH) codes under the Z-code chapter, expanded specificity in cardiovascular and metabolic diagnoses, and new codes reflecting post-COVID-19 condition documentation.
Key ICD-10 Coding Guidelines Every Coder Must Know
Code to the highest level of specificity — Always assign the most specific code supported by clinical documentation. Using an unspecified code when a more specific code exists is an audit risk and often triggers payer coverage reviews.
Principal diagnosis sequencing — For inpatient encounters, the principal diagnosis is the condition established after study to be chiefly responsible for the admission. Incorrect sequencing is one of the most common inpatient coding errors and directly affects DRG assignment and reimbursement.
Signs and symptoms vs definitive diagnoses — For outpatient encounters, code the condition to the highest degree of certainty. Do not code a condition as confirmed if the physician has documented it as suspected, probable, or rule-out.
Combination codes — ICD-10-CM includes many combination codes that capture both a condition and its complication or cause in a single code. Using the combination code instead of two separate codes is required when the combination code fully describes the clinical situation.
How AI Coding Handles ICD-10 Updates
Medicodio updates CODIO with each annual ICD-10-CM release and each quarterly CPT update automatically. Coders using manual encoder tools must manually update their reference databases with each release — and any lag creates audit exposure. For a full guide on training tools and NCCI lookup resources, see the medical coding training software guide .
Frequently Asked Questions
When does ICD-10 update each year? ICD-10-CM updates take effect October 1 annually. CMS publishes the new code tables and guidelines each spring, giving organisations several months to update training and coding systems before the effective date.
What happens if you use an invalid ICD-10 code? The claim is denied for an invalid code. The coder must correct the code, update the claim, and resubmit within the payer's filing deadline. For high-volume coding, using an AI platform that auto-updates with each code release prevents this systematically.