Question 1

What is ICD-10 code F99?

Accepted Answer

F99 is the ICD-10-CM diagnosis code for mental disorder, not otherwise specified. A mental health disorder that cannot be classified into any other specific mental disorder category. F99 sits in the ICD-10-CM chapter for mental, behavioral and neurodevelopmental disorders (f01-f99), within the section covering unspecified mental disorder (f99).

F99 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 last-resort code; ensure all documentation has been reviewed for a more specific mental health diagnosis.

Question 2

Is F99 an HCC code?

Accepted Answer

No. F99 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 F99 billable?

Accepted Answer

Yes. F99 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. F99 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 F99?

Accepted Answer

F99 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 community model rewards F99 with a risk adjustment factor, it contributes zero to a Medicare Advantage beneficiary's V28/V24 community RAF score in either version. Coders should check whether provider documentation supports a more specific child code that does map to a community payment HCC.

Question 5

What should coders know when reporting F99?

Accepted Answer

This is a last-resort code; ensure all documentation has been reviewed for a more specific mental health diagnosis Consider querying the provider if symptoms are documented but a specific diagnosis is not assigned

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F99

Is F99 an HCC code?

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Coding Tips

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F99 ICD-10-CM Code: Mental disorder, not otherwise specified

HCC Buddy Code Card

F99

Is F99 an HCC code?

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What This Code Means

Coding Tips

Excludes 1, Do NOT code together

Code Hierarchy

Work F99 in HCC Buddy