Question 1

What is ICD-10 code F09?

Accepted Answer

F09 is the ICD-10-CM diagnosis code for unspecified mental disorder due to known physiological condition. A mental health disorder caused by a known medical condition when the specific type of mental disorder cannot be determined or is not specified. F09 sits in the ICD-10-CM chapter for mental, behavioral and neurodevelopmental disorders (f01-f99), within the section covering mental disorders due to known physiological conditions (f01-f09).

F09 is a billable ICD-10-CM code but does not map to a payment HCC under the CMS-HCC V28, V24, ESRD, or RxHCC risk adjustment models. It can be reported on Medicare Advantage encounter data submissions but it does not contribute to a beneficiary's RAF score and therefore does not affect risk-adjusted payments to the plan.

This is a catch-all code for mental disorders due to medical conditions that don't fit other specific categories.

Question 2

Is F09 an HCC code?

Accepted Answer

No. F09 is a billable ICD-10-CM code but does not map to any payment HCC category under the CMS-HCC V28, V24, ESRD, or RxHCC risk adjustment models. It can still be reported on Medicare Advantage encounter data submissions, but it does not contribute to the beneficiary's Risk Adjustment Factor (RAF) score and therefore does not affect the risk-adjusted capitation payment to the plan. V28 reached 100% phase-in for payment year 2026.

Question 3

Is F09 billable?

Accepted Answer

Yes. F09 is a billable ICD-10-CM code that can be reported on professional and institutional claims as a primary or secondary diagnosis when the provider documentation supports the specific condition described. Billable codes in ICD-10-CM are coded to the highest level of specificity available for the documented diagnosis. F09 is current for fiscal year 2026 and remains in the active CMS ICD-10-CM code set published by the National Center for Health Statistics.

Question 4

What is the V28 vs V24 difference for F09?

Accepted Answer

F09 does not map to a payment HCC under either the CMS-HCC V28 risk adjustment model or the older V24 model. V28 reached 100% phase-in for payment year 2026, replacing V24 which was used during the PY2024–PY2025 transition. Because neither model rewards F09 with a risk adjustment factor, it contributes zero to a Medicare Advantage beneficiary's RAF score in either version. Coders should check whether provider documentation supports a more specific child code that does map to a payment HCC.

Question 5

What should coders know when reporting F09?

Accepted Answer

This is a catch-all code for mental disorders due to medical conditions that don't fit other specific categories Document the underlying medical condition and attempt to specify the mental disorder type when possible

F09

Is F09 an HCC code?

What This Code Means

Coding Tips

Excludes 1 — Do NOT code together

Code First

Code Hierarchy

Open F09 in the Interactive Encoder