The ICD-10-CM update cycle

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

Applies to ICD-10-CM FY2027 · October 1, 2026 – September 30, 2027

The short answer

The main ICD-10-CM update takes effect October 1 each year and defines the fiscal year. A secondary update can take effect April 1. There is no grace period, and the code set that applies is decided by the date of service — not the date you submit the claim.

Date of service, not date of billing

This is the rule that causes the most avoidable rejections. A claim submitted in November for an encounter that happened in September must use the previous fiscal year’s codes. Billing late does not move an encounter into the new code set, and an encoder defaulting to “current year” will quietly get it wrong.

There is no transition window

Unlike some coding systems, ICD-10-CM has no grace period during which both the old and new code apply. On October 1, 2026 the new set is in force for encounters from that date, and the old set continues to apply to earlier encounters indefinitely.

The April 1 update is real

ICD-10-CM is commonly described as an annual code set, which is no longer accurate. CMS and the CDC operate a twice-yearly cycle, and April 1 updates do get published — FY2026 had one, distributed as its own release with its own addenda and guidelines. It is a smaller update than October, and it is the one most likely to be missed because nobody is expecting it.

What changed this year

FY2027, effective October 1, 2026

190 codes added
30 billable codes deleted — of which 15 were subdivided into more specific codes and 15 were retired outright
6 header codes removed (never billable, so no claim impact)
4 descriptions revised

See every change with its replacement code →

The change most likely to cost you money

Subdivision, not deletion

When a billable code is subdivided, it does not disappear. It stays in the classification as a non-billable header while its new children take over. That means it still resolves in every lookup, still looks completely normal, and simply starts being denied for lack of specificity.

A retired code fails loudly — your clearinghouse rejects it as invalid and someone investigates. A subdivided code fails quietly, often weeks later, as a specificity denial that looks like a documentation problem rather than a code-set problem. FY2027 has 15 of these.

What to do each October

Check your high-volume codes first. A subdivision affecting one of your top twenty codes matters far more than twenty changes you never report.
Look specifically for subdivisions, not just additions and deletions. Deletion lists published by vendors often conflate the two.
Update superbills and favourites lists. Cached shortcuts are where retired codes survive longest.
Confirm your encoder switched over — and that it still lets you code prior-year encounters correctly.
Diary the April 1 window. Most teams do not.

This site rebuilds from the official release for each update and records every release on the changelog. Prior-year codes are not deleted, because they remain correct for encounters within their own fiscal year. See data sources for the files used.