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The FY 2027 ICD-10-CM codes take effect October 1

A new diagnosis code set arrives every October. Here is how to get a practice ready in the week that matters most, without memorizing the addenda.

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The short version

  • The FY 2027 ICD-10-CM code set applies to encounters from October 1, 2026 through September 30, 2027.
  • Claims with deleted or invalid codes are rejected, and those rejections cluster in the first weeks of October.
  • September dates of service billed late still use last year's codes.
  • Checking your top 50 codes against the addenda covers most of the risk.

Every year on October 1, the diagnosis code set changes. New codes appear, some are deleted and some descriptions are revised. A claim for a visit on September 30 uses last year's codes; a claim for October 1 uses the new ones. Payers reject claims with deleted or invalid codes, and in our experience those rejections pile up in the first two weeks of October, just as everyone is busy with something else.

CMS posted the FY 2027 ICD-10-CM files in June 2026: the code tables, the tabular list and index, the addenda that show what changed, and a conversion table that maps old codes to new ones. The code set applies to patient encounters from October 1, 2026 through September 30, 2027. When the files first posted, the FY 2027 official coding guidelines had not been published yet, so check CMS for the final version before you train anyone on them.

Oct 1
The date FY 2027 ICD-10-CM codes start to apply. They cover encounters through September 30, 2027.Source: CMS

Why October catches practices out

The code set itself is rarely the problem. The problem is every place in the practice where last year's codes are saved and reused without anyone looking at them.

  • Favorite lists, templates and order sets in the EHR still point to deleted codes.
  • Superbills and charge sheets were printed once and have been used for years.
  • A code that gains a new level of detail stops being billable as written, even though it still looks familiar.
  • Claims for September dates of service that go out in October still need the old codes, and some systems apply the new set by billing date instead of service date.

A one-week plan

You do not need to read every addendum line. Most practices use a small set of diagnosis codes for most of their claims, so that is where to look first.

  1. Pull the practice's 50 most-used diagnosis codes from the last twelve months.
  2. Check each one against the FY 2027 addenda and conversion table, and note anything deleted, expanded or revised.
  3. Update EHR favorites, order sets and any paper superbills before October 1.
  4. Give each provider the changes in their own specialty, with one example each, instead of the whole addendum.
  5. Watch clearinghouse rejections for invalid-code edits every day through mid-October.

Also check April

CMS now also publishes an April 1 update to the ICD-10 code sets. It is usually much smaller than the October release, but the same checks apply: compare it against your most-used codes and update templates before the date arrives.

Before October 1

  • Top 50 diagnosis codes checked against the FY 2027 addenda
  • EHR favorites and order sets updated
  • Paper superbills reprinted or retired
  • Late September claims confirmed to use FY 2026 codes
  • Daily rejection review scheduled for the first two weeks of October

Sources

  1. CMSICD-10 code sets and FY 2027 files
  2. CDC National Center for Health StatisticsICD-10-CM
  3. AHCA/NCALCMS posts FY 2027 ICD-10-CM update effective Oct. 1

These articles are general information for practice owners and managers. They are not legal, coding or compliance advice. Payer rules change and vary by plan and state, so check the current source before you act on anything here.

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