ICD-10-CM 2027
ICD-10 code for chronic daily headache
From the official ICD-10-CM alphabetic index entry “Headache › chronic daily”. Page updated September 29, 2026.
About coding chronic daily headache
The ICD-10-CM code for chronic daily headache is R51.9 (Headache, unspecified).
Within R51, choose R51.9 (unspecified) only when documentation doesn't support a more specific option: with orthostatic component, not elsewhere classified (R51.0).
It is not a CC or MCC, so as a secondary diagnosis it doesn't change the MS-DRG severity level.
In MS-DRG v44.0, it is part of the grouping logic for DRG 102 (Headaches with MCC, relative weight 1.1201) and DRG 103 (Headaches without MCC, relative weight 0.822), in MDC 01 (Diseases and Disorders of the Nervous System), as a principal or secondary diagnosis. The DRG a claim lands in depends on the principal diagnosis, procedures and any CC/MCC secondary diagnoses.
Common questions about chronic daily headache ICD-10 codes
What is the ICD-10 code for chronic daily headache?
- R51.9 — Headache, unspecified.
Is R51.9 billable?
- Yes. R51.9 is a billable/specific ICD-10-CM code valid for FY2027 (October 1, 2026 – September 30, 2027).
Can R51.9 be used as a principal diagnosis?
- Yes. The Medicare Code Editor doesn't restrict R51.9 as a principal diagnosis.
Is R51.9 a CC or MCC?
- No. R51.9 is neither a CC nor an MCC under MS-DRG v44.0.