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The ICD-10 code changes for 2026 took effect on October 1, 2025, and they are still catching small practices off guard. The fiscal year 2026 update adds 487 new diagnosis codes, revises 38, and deletes 28. A deleted code is not a suggestion to code differently someday — it is an invalid code, and a claim carrying one can be rejected before a payer ever adjudicates it. If your electronic health record (EHR) still offers a deleted code in a picklist, or a favorite code set has not been refreshed since last September, that rejection is only a matter of time. This guide walks through what changed, which updates matter most for a small practice, and the exact checks that stop deleted-code rejections. If you would rather hand the cleanup to a coding team, our medical coding and credentialing services include code-set updates, charge-master review, and denial follow-up.
The FY 2026 ICD-10-CM code set applies to patient encounters and discharges from October 1, 2025, through September 30, 2026. The governing rule is the date of service, not the date you submit the claim: a visit on September 30, 2025, uses the old code set, while a visit on October 1 uses the new one. Claims that straddle the changeover, corrected claims, and rebilled claims are where this rule most often trips practices up, so check the date of service first whenever a code looks questionable.
| Change type | FY 2026 count | What it means for your practice |
|---|---|---|
| New codes | 487 | More specific options for conditions that previously shared one code. |
| Revised codes | 38 | Titles or descriptions changed; confirm the code still means what you think it means. |
| Deleted codes | 28 | Invalid from October 1, 2025; claims using them can be rejected outright. |
| Total code changes | 553 | The full update, published by CMS and the CDC, for FY 2026. |
The headline numbers only tell part of the story. Two chapters carry most of the new codes, and both reward documentation that is more specific than many practices currently capture. Chapter 19, covering injury and poisoning, adds 213 new codes for greater detail on injuries. Chapter 12, covering skin and subcutaneous tissue, adds 116 new codes, largely for non-pressure chronic ulcers now classified by anatomical site and severity. If your practice treats wounds, injuries, or post-acute patients, those two chapters deserve a dedicated review rather than a quick skim of the update summary.
When a code is deleted, it is removed from the valid code set. It does not become a warning, and it does not map automatically to a replacement on the claim. A scrubber or clearinghouse may flag it, but if it slips through, the payer can reject the claim as invalid — which is different from a denial. A rejection means the claim was never accepted for processing, so there is nothing to appeal until you correct the code and resubmit. That distinction matters for timely filing: the clock does not pause while a rejected claim sits unnoticed in a work queue.
Deleted codes are generally replaced by more specific codes rather than simply vanishing, so the fix is usually a code change, not a documentation rewrite. The official list of invalid codes is published in Table 6C of the FY 2026 inpatient prospective payment system final rule, and the CMS code files are the authoritative source. Do not rely on a blog summary — including this one — as your deleted-code list. Download the official tables, search your EHR picklists, favorites, templates, and superbills for every deleted code, and remove or replace each one. Then check the less obvious places: standing orders, patient-education handouts that print codes, and any spreadsheet your front desk uses to look codes up.
One more trap deserves attention. A code can stop being billable without being deleted at all. Some codes that were once complete now require additional characters to be valid. The classic FY 2026 examples are multiple sclerosis and financial insecurity, discussed below. A coder who types the old, shorter code and moves on will produce the same rejection as a deleted code, with no deletion involved.
Most of the 487 new codes will never touch a given practice, so focus on the additions that change everyday coding decisions.
FY 2026 introduces E11.A, type 2 diabetes mellitus without complications in remission. Before this code existed, practices had no clean way to report a patient whose type 2 diabetes was in remission, and coders were left forcing the diagnosis into a code that implied active disease. Use E11.A only when the clinical documentation supports remission; it is not a code for well-controlled diabetes, and it should never be assigned from a lab value alone.
Previously, G35 (multiple sclerosis) was a complete code on its own. From October 1, 2025, G35 requires additional characters identifying the disease phenotype, with new codes in the G35.0–G35.9 range. Any template, favorite, or auto-populated problem list that still carries bare G35 needs updating, and clinicians documenting multiple sclerosis should now specify the phenotype so coders can select the right code.
Similarly, Z59.86 is no longer a complete code. It now requires additional characters, including Z59.861 for financial insecurity with difficulty paying for utilities. These social-determinants codes matter for practices that screen for them, and they are a good reminder to check any Z-code favorites, not just diagnosis codes tied to procedures.
The update also expands codes for conditions such as hyperoxaluria and other rare metabolic disorders, adds codes for acariasis (mite infestations, including Demodex dermatitis) under B88.0-, and continues the long-running shift toward codes that capture site, severity, and laterality. The practical lesson is consistent across chapters: if your documentation already records the site and severity, the new codes are an opportunity. If it does not, the new codes will expose the gap.
Deleted codes get the attention, but specificity errors cause at least as many rejections in a code-change year. Watch for these five:
The fix for all five is unglamorous: slow down at the point of code selection, and make the EHR do the work. Remove invalid options from picklists rather than training staff to avoid them, because a code that cannot be selected cannot be billed by mistake.
Use this workflow once for the FY 2026 update, then keep it as your annual routine — the code set changes every October 1, and the practices that struggle are the ones that treat each update as a surprise.
| Step | Action | Done when… |
|---|---|---|
| 1. Download the official files | Get the FY 2026 code tables and guidelines from CMS/CDC. | You have the deleted-code list and the new-code list in hand. |
| 2. Search every code repository | Check EHR picklists, favorites, templates, superbills, and problem lists. | Every deleted code is removed or replaced, and every new code your practice uses is available. |
| 3. Update documentation prompts | Add site, severity, phenotype, and laterality prompts where new codes require them. | Clinicians can document the new detail without a coder chasing them. |
| 4. Test before you bill | Run test claims or scrubber checks with the new codes. | Test claims pass without invalid-code edits. |
| 5. Monitor rejections for 30 days | Review rejection reports weekly, grouped by reason code. | Invalid-code rejections fall to zero and stay there. |
Step 5 is the one most practices skip, and it is the one that catches the codes hiding in rarely used templates. A single weekly review of rejection reasons for the first month after October 1 will surface stragglers — a specialty template, a locum’s favorite set, a payer-specific workflow — while they are still cheap to fix.
If a claim has already been rejected, work it in this order. First, confirm the rejection reason is truly an invalid code and not a payer-specific edit. Second, identify the correct replacement code from the current code set, and confirm the documentation supports it — if it does not, query the clinician rather than guessing. Third, correct and resubmit the claim, and check the payer’s timely filing limit before you assume you have time; our guide to timely filing limits by payer shows how quickly those windows close. Fourth, fix the source: remove the deleted code from whatever picklist or template produced it, so the same claim does not reject again next week. Finally, log the pattern. One deleted-code rejection is a typo; five from the same template is a system problem.
For a broader view of how coding mistakes turn into lost revenue, see our list of medical coding errors that trigger denials — several of the same habits that cause denials also cause code-set rejections. And remember that diagnosis codes are only half the update story: the CPT code changes for 2026 brought their own deleted procedure codes, so a practice that updated ICD-10 but not CPT is only half protected.
The FY 2026 ICD-10-CM code set took effect on October 1, 2025, and applies to encounters and discharges from that date through September 30, 2026. Which code set applies is determined by the date of service, not the submission date.
The FY 2026 update adds 487 new codes, revises 38, and deletes 28, for 553 total code changes. The largest groups of new codes are in the injury chapter (213 codes) and the skin chapter (116 codes).
A deleted code is invalid, so the claim can be rejected before adjudication. A rejection is not a denial: you must correct the code and resubmit, and the timely filing clock keeps running while the claim sits uncorrected.
The authoritative sources are the CMS and CDC FY 2026 code files. The deleted codes appear in Table 6C of the FY 2026 inpatient prospective payment system final rule. Use those tables to audit your EHR, rather than relying on any summary list.
No. Codes are selected based on the code set in effect on the date of service. A September 2025 visit keeps the old code set even if you correct or rebill it after October 1, 2025.
Search every place codes live — EHR picklists, favorites, templates, superbills, and problem lists — against the official deleted-code list, then run your scrubber or test claims and monitor rejection reports weekly for the first month.
The FY 2026 ICD-10 update rewards one habit above all: keeping your code lists as current as your clinical knowledge. Download the official tables, purge the 28 deleted codes from every picklist and template, update the codes that now require extra characters, and watch your rejection reports for a month. That single pass prevents a class of rejections that costs small practices real revenue and real staff time. If your team is short on coding bandwidth, or the cleanup keeps surfacing in new templates, contact UMB and Coding or call 201-942-0949 for a coding review — we can audit your code lists, update your charge master, and work the rejections that have already landed.
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