The onychomycosis ICD-10 code is B35.1, tinea unguium, in the FY2027 ICD-10-CM set effective October 1, 2026. One code covers toenails and fingernails. Use B37.2 for candida, L60.3 for dystrophy alone or L03.03- for toe cellulitis only when the provider documents them. B35.1 on a Medicare claim does not by itself make the visit payable.
Most nail fungus denials are not caused by the wrong code for onychomycosis. They come from the codes and documentation around it. This guide is based on the ICD-10-CM listings we read on October 14, 2026, and it replaces an older version of this post that mislabeled several related codes. We corrected those and removed statistics we could not source.
It is written for practice owners, coders and billing leads. It is general education, not coding or clinical advice, and the code set and payer rules change each year.
Key takeaways
- B35.1 (tinea unguium) is the ICD-10-CM code for onychomycosis, for toenails and fingernails alike.
- The FY2027 code set runs October 1, 2026 to September 30, 2027, and the listings we read show no changes in the nail fungus ranges.
- B37.2, L60.3 and L03.03- are different conditions. Do not swap them in without provider documentation.
- A diagnosis code does not decide payment. Medicare contractors and Medicare Advantage plans add their own documentation rules.
Which ICD-10-CM code is onychomycosis?
Onychomycosis is coded B35.1. The official title is “Tinea unguium,” and the code lists dermatophytic onychia, dermatophytosis of nail, onychomycosis and ringworm of nails as terms under it (AAPC). It sits in category B35, dermatophytosis, which includes infections due to Epidermophyton, Microsporum and Trichophyton and tinea of any type except those in B36 (ICD-10 code listing, FY2027).
B35.1 is a complete, billable code. It has no sixth or seventh character, so there is no right or left, and no toe versus finger split (HCC Buddy FY2027 listing). That matters for the claim. The code says what the diagnosis is. The note and the procedure line have to say which nails were treated and what was done.
Which code-set year applies
CMS states that the FY2027 ICD-10-CM codes apply to discharges and encounters from October 1, 2026 through September 30, 2027 (CMS). A published FY2027 comparison lists no added, removed or changed entries in B35, B36, B37, L03.0 or L60, the ranges used in this post (HCC Buddy FY2027 changelog). The official FY2027 files are posted by NCHS, so check the file for your date of service.
Table 1 lists B35.1 beside the codes that get mixed up with it.
| Code | Official title | Use it when the provider documents | Common mix-up |
|---|---|---|---|
| B35.1 | Tinea unguium | Onychomycosis, fungal nail infection, or ringworm of the nails | Assigned from nail appearance alone, with no provider diagnosis |
| B35.3 | Tinea pedis | A fungal infection of the skin of the foot (athlete’s foot) | Added automatically to every nail fungus claim |
| B37.2 | Candidiasis of skin and nail | A candida nail infection, including candidal onychia or paronychia | B35.1 used for every nail fungus, including candida |
| L60.3 | Nail dystrophy | A dystrophic nail with no fungal diagnosis | Added beside B35.1 when the provider never called the nail dystrophic |
| L60.8 | Other nail disorders | A specified nail disorder that has no better code | Used as a catch-all in place of a documented diagnosis |
| L03.031, L03.032, L03.039 | Cellulitis of right, left or unspecified toe | Cellulitis of a toe, including nail infection, onychia or paronychia | Described as “caused by fungal infection.” It is not a fungal code |
Source: ICD-10-CM FY2027 listings as mirrored by icd-10codes.com (B35), HCC Buddy (B35.1, B37.2), Unbound Medicine (L60) and RapidClaims codebook (L03.03). Titles are the official short titles; usage notes are our summary.
What the Excludes notes mean for nail fungus
B35.1 carries no Excludes1 note of its own. The listings we read show no Excludes1 at B35 either, so nothing in the tabular list stops B35.1 from sitting on a claim next to the other nail and foot codes, provided each is documented. The notes that do exist are Excludes2 notes inherited from the chapter and section, for example carrier status (Z22.-), hypersensitivity pneumonitis due to organic dust (J67.-) and mycosis fungoides (C84.0-) (icd-10codes.com).
Plainly: an Excludes1 note means two conditions should not be coded together. An Excludes2 note means they may be reported together when both are present. The chapter-level notes above are not nail-related, so they rarely come up on a podiatry claim.
| Code or category | Note in the tabular list | What it means in practice |
|---|---|---|
| B35 (dermatophytosis) | Includes tinea of any type except those in B36 | B36 conditions are coded in B36, not here |
| B35.1 | No Excludes1 or Excludes2 at the code level | No tabular conflict with B35.3 or L60.3 when both are documented |
| B37.2 | Excludes2: diaper dermatitis (L22) | Rarely relevant to adult nail claims |
| L03.03 (toe) | Applicable to infection of nail, onychia, paronychia, perionychia | A bacterial-type toe nail infection codes here, not to B35.1 |
| L03.11 | Excludes2: cellulitis of toes (L03.03-) | Do not use the generic limb cellulitis code for a toe |
Source: ICD-10-CM FY2027 listings as mirrored by icd-10codes.com (B35), HCC Buddy (B37.2) and RapidClaims codebook (L03.03, L03.11). Mirrors can lag; confirm against the CMS or NCHS tabular file.
One more point on provider documentation. If the provider names an organism that is not a dermatophyte, or the note says the nail infection is something other than fungus, do not default to B35.1. Query the provider and check the Alphabetic Index entry for the exact term in the note.
What the note needs to support B35.1
The provider’s diagnosis supports the code. A coder should not assign B35.1 because a nail is thick or yellow. The note needs the diagnosis in the provider’s words, and for most payers it needs more than that.
- The diagnosis. “Onychomycosis,” “fungal nail infection” or “tinea unguium,” stated by the provider, not inferred.
- Which nails. Toenails or fingernails, and which ones. B35.1 does not carry this, so the note must.
- Why it was treated. Pain, secondary infection or limited walking attributable to the nail. Payers often ask for this.
- What was done. The procedure, such as debridement, so the claim line matches the note.
- Other conditions that change the rules. For Medicare patients, a qualifying systemic or vascular condition and any required physician details.
Payer wording varies. A Kaiser Permanente Medicare clinical review (reviewed August 2025) covers mycotic toenail treatment when the attending physician documents clinical evidence of mycosis and the patient has pain or secondary infection from the thickened, dystrophic nail plate. For patients who are typically ambulatory it asks for marked limitation of ambulation attributable to the toenail mycosis (Kaiser Permanente). A Noridian Medicare billing article (revision effective October 1, 2025) says that when the mycotic toenail causes no pain, the treating provider must clearly state what other impediment the treatment addresses (Noridian A57954). Your own contractor or plan may differ, so use its current article.
Why B35.1 alone does not decide payment
A correct diagnosis code gets the claim onto the right path. It does not make the service payable. Nail care is where Medicare’s routine foot care rules apply, and those rules turn on the patient’s condition, the findings in the chart and modifiers on the procedure line. We cover the exclusion, the Q7, Q8 and Q9 modifiers and the foot care procedure codes in our routine foot care billing guide. Start there before you build billing rules for nail debridement.
For the procedure side, the nail debridement codes are 11720 and 11721. A podiatry conference deck dated 2021 lists 11720 as debridement of nails, one to five (APMA conference deck). 11721 is the higher-count code. Confirm the exact descriptor in the current AMA CPT code set, because AMA owns it. The same deck pairs B35.1, L60.3 and L60.8 as secondary diagnoses with those codes in its Noridian-region example. That is one contractor’s approach, from 2021, and not a national rule.
This is also where a specialty-aware workflow helps. Podiatry claims depend on documented findings, laterality of the procedure and payer-specific edits, which is why we handle them in our podiatry billing and coding support. Our medical billing services team checks the diagnosis, the procedure line and the payer article together before submission.
| Check | Why it matters | Who owns it |
|---|---|---|
| Provider documented the diagnosis in words | B35.1 is defined by the diagnosis term, not by appearance | Provider, then coder |
| Candida or other organism ruled in or out | B37.2 and B35.1 are different codes | Coder queries provider |
| Cellulitis or paronychia coded separately if documented | L03.03- is its own condition, not a fungal code | Coder |
| Payer article opened for the date of service | Rules and required diagnoses vary by contractor and plan | Billing lead |
| Procedure line matches the nails treated | Count and site must agree with the note | Biller |
| Qualifying conditions and physician details present (Medicare) | Required by some contractors for systemic-condition coverage | Coder and biller |
Want a second look at your podiatry claims?
Send us a sample of recent nail care denials and we will show you which diagnosis, modifier or documentation gap caused each one. No obligation.
A claim-centred system makes these checks repeatable. A practice management system that tracks claims by stage can flag missing data before submission and show who owns each open claim. It is not an EHR, and it does not replace the provider’s documentation.
Mistakes the older version of this post made, and how to avoid them
We reviewed the earlier post line by line against the code listings. These are the corrections, because the same errors turn up in real claim queues.
- Calling L03.03 and L03.01 fungal. They are cellulitis of the toe and the finger. Code them only when the provider documents cellulitis or a nail infection of that kind.
- Using B35.1 for every nail infection. Candida goes to B37.2 when documented. Do not guess the organism.
- Adding unrelated B35 codes. Tinea corporis, cruris or capitis belong on the claim only when the provider treats and documents them at that visit.
- Listing diabetic dermatitis as the diabetes code for foot care. The older post paired E11.620 with onychomycosis. That code is not a nail fungus companion, and the diabetic foot rules sit in the Medicare guide linked above.
- Ignoring the payer article. A correct B35.1 can still be denied for missing findings or physician details.
If you are unsure how to pair diabetes codes with foot care, start with our diabetes ICD-10 codes guide, then check your contractor’s article. For general code and modifier background, see CPT, ICD-10 and HCPCS codes explained.
Keeping nail fungus claims clean
Denials on these claims usually trace back to a mismatch between the note, the diagnosis and the procedure line. The fix is a short, repeatable check at coding time and a scrub before submission. Our guides on clean claims and medical coding audits describe the method. If a nail fungus claim does deny, our denial management services team works from the payer’s remark codes, not from guesses.
Patients also ask providers about skin and nail problems that sit outside podiatry. For fungal skin conditions treated in dermatology, see our guide to dermatology services and insurance coverage.
Our recommendations
- Code from the provider's words. We tell coders to assign B35.1 only when the note says onychomycosis, fungal nail infection or tinea unguium. If the note only describes thick or discolored nails, we send a query.
- Keep a one-page look-alike chart. We keep B35.1, B37.2, L60.3 and L03.03- on one page with their official titles, so nobody labels cellulitis as a fungal code again.
- Open the payer article for every contractor. We save the contractor’s foot care article and its revision date beside the rule it supports. Requirements for diagnoses, modifiers and physician details differ.
- Match the claim line to the note. We check that the number and site of nails in the note agree with the procedure line before the claim leaves.
- Re-check codes each October 1. We review the new ICD-10-CM files each fall, even when the nail ranges look unchanged, and update our edits the same week.
Track each nail care claim by stage, with an owner.
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Bottom line
The onychomycosis ICD-10 code is B35.1, and the work is in what surrounds it: the provider’s diagnosis, the right look-alike code when the facts differ and the payer’s documentation rules. If your podiatry claims keep denying around these points, our denial management services team can review them, or you can contact us for a free practice audit. You can also estimate what unworked denials cost with the revenue calculator.
Frequently asked questions
What is the ICD-10 code for toenail fungus?
The ICD-10-CM code for toenail fungus is B35.1, tinea unguium. It is the same code for fungal infection of a fingernail, and it has no laterality. The provider’s note has to say which nails were involved. Use other codes only when the provider documents a different condition.
Is B35.1 specific to dermatophytes?
B35.1 sits in category B35, which includes infections due to Epidermophyton, Microsporum and Trichophyton. Onychomycosis is listed under it as a term. If a provider documents candida, code B37.2 instead. If the organism is something else, query the provider and check the Alphabetic Index.
Can I report B35.1 with tinea pedis?
Yes, when the provider documents both. B35.3 is tinea pedis, and the tabular list shows no Excludes1 note between B35.3 and B35.1. Do not add B35.3 automatically. Each condition needs its own documentation at that visit.
Is cellulitis of the toe a fungal code?
No. L03.031, L03.032 and L03.039 are cellulitis of the right, left or unspecified toe. The category also covers nail infection, onychia and paronychia. Code it only when the provider documents that condition, and do not describe it as a fungal infection.
Does Medicare pay for onychomycosis treatment?
Not automatically. Routine foot care is excluded unless an exception applies, and contractors set their own documentation rules. Our routine foot care guide covers the exclusion, the Q7 to Q9 modifiers and the procedure codes. Always open your Medicare contractor’s current article for the date of service.
Did the ICD-10 code for onychomycosis change for FY2027?
We found no change. A published FY2027 comparison lists no added, removed or changed entries in the B35, B36, B37, L03.0 or L60 ranges. The FY2027 set applies from October 1, 2026 through September 30, 2027. Check the official CMS or NCHS files for your date of service.
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Sources
- ICD-10 codes (FY2027 section) — CMS (2026)
- ICD10CM 2027 file directory — CDC NCHS (2026)
- B35 Dermatophytosis (FY2027) — icd-10codes.com (2026)
- B35.1 Tinea unguium (FY2027) — HCC Buddy (2026)
- ICD-10-CM B35.1 — AAPC (2026)
- FY2027 ICD-10-CM changelog — HCC Buddy (2026)
- B37.2 Candidiasis of skin and nail (FY2027) — HCC Buddy (2026)
- L03.03 Cellulitis of toe — RapidClaims codebook (2026)
- L60 Nail disorders — Unbound Medicine ICD-10-CM (2026)
- Billing and Coding: Routine Foot Care (A57954) R20 — Noridian Healthcare Solutions (2025)
- Routine Foot Care Medicare clinical review — Kaiser Permanente (2025)
- Routine foot care billing and coding deck — Podiatry conference materials (G. Halperin, DPM) (2021)
Disclaimer: This post is general educational information about revenue cycle operations. It is not legal, coding, billing-compliance or clinical advice. ICD-10-CM codes are updated each year, and Medicare contractor and payer policies vary. CPT is a registered trademark of the American Medical Association. Confirm current codes and requirements with the official ICD-10-CM files, the AMA CPT code set, CMS, your contractor and each payer before you bill.
