Onychomycosis Severity Index (OSI)
Onychomycosis Severity Index (Carney 2011): grades a single fungal nail as area of involvement multiplied by proximity to the matrix, plus 10 points if a dermatophytoma or > 2 mm subungual hyperkeratosis is present.
Open the calculator → Runs in your browser. Data leaves only if you deliberately send a problem report from the interactive tool.
Example
- Area of involvement
- 3 — 26–50%
- Proximity to matrix
- 4 — proximal quarter
Result: OSI 12/35 — moderate.
The tool opens with these values already filled in. Replace them with your own.
What the result means
- 0 / 1-5
- no involvement / mild.
- 6-15 / 16-35
- moderate / severe.
What you enter
- Area of involvement (0 none, 1 = 1-10%, 2 = 11-25%, 3 = 26-50%, 4 = 51-75%, 5 = >75%)
- Proximity to matrix (1 distal quarter, 2 second, 3 third, 4 proximal quarter, 5 matrix)
- Dermatophytoma (streak/patch) or > 2 mm subungual hyperkeratosis (+10)
How this is calculated
- Formula
- area of involvement (0-5) × proximity to the matrix (1-5) + 10 if a dermatophytoma or > 2 mm subungual hyperkeratosis is present.
Carney C, Tosti A, Daniel R, Scher R, Rich P, DeCoster J, Elewski B. A new classification system for grading the severity of onychomycosis: Onychomycosis Severity Index. Arch Dermatol. 2011;147(11):1277-1282. Read the source ↗
A reference and educational tool. Not medical, legal, or financial advice, and not a substitute for clinician judgment.