G40.309
BillableGeneralized idiopathic epilepsy and epileptic syndromes, not intractable, without status epilepticus
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is G40.309 an HCC code?
Yes. G40.309 maps to Seizure Disorders and Convulsions under the CMS-HCC V28 risk adjustment model (and Seizure Disorders and Convulsions under V24).
HCC Category Mapping
RAF weights shown are the community, non-dual, aged base weights from the CMS risk adjustment model file. Actual per-patient RAF contribution depends on member segment, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains in use during the transition and for historical data.
MEAT Criteria for G40.309
For G40.309 to count as a valid HCC diagnosis in a given encounter, the provider's documentation must show MEAT: Monitor, Evaluate, Assess, or Treat. A diagnosis from a prior year does not carry forward automatically — it has to be re-documented and supported each calendar year.
- MMonitor: signs, symptoms, disease progression, or lab trending documented in the note
- EEvaluate: test results, medication response, or physical findings reviewed by the provider
- AAssess: explicit mention in the assessment or plan with acknowledgment of status
- TTreat: medication, referral, procedure, therapy, or counseling tied to the diagnosis
Only one of M/E/A/T is required to support the code, but the documentation must be specific enough to show that the provider actually addressed G40.309 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
G40.309 is the ICD-10-CM diagnosis code for generalized idiopathic epilepsy and epileptic syndromes, not intractable, without status epilepticus. A generalized epilepsy that affects the entire brain from the start and is controllable with medication, and the patient is not currently in status epilepticus. G40.309 sits in the ICD-10-CM chapter for diseases of the nervous system (g00-g99), within the section covering episodic and paroxysmal disorders (g40-g47).
Under the CMS-HCC V28 risk adjustment model, G40.309 maps to Seizure Disorders and Convulsions (HCC 201) with a community, non-dual, aged base RAF weight of 0.262. Under the older V24 model, G40.309 mapped to the same category but with a base RAF weight of 0.244 — V28 recalibrated weights across the entire model. V28 is the CMS-HCC risk adjustment model that reached 100% phase-in for payment year 2026, replacing V24 which was used during the PY2024–PY2025 transition.
This code represents well-controlled generalized idiopathic epilepsy without acute seizure complications. Because G40.309 maps to a payment HCC, the provider's documentation must satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's Medicare Advantage risk adjustment score. When documentation is ambiguous, coders should issue a provider query rather than assume the highest-specificity variant.
HCC Buddy maintains structured V28 and V24 mapping, RAF weights, and MEAT documentation criteria for G40.309 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •This code represents well-controlled generalized idiopathic epilepsy without acute seizure complications
- •Document medication regimen and seizure frequency to establish the 'not intractable' status
Clinical Significance
This code represents the stable, well-controlled state of generalized idiopathic epilepsy — the most commonly coded presentation for patients with generalized epilepsy of unknown cause. It includes conditions like juvenile myoclonic epilepsy and childhood absence epilepsy when well-managed. Annual recapture of this diagnosis is essential for ongoing risk adjustment.
Documentation Requirements
- ✓Documentation of generalized epilepsy (bilateral onset)
- ✓Idiopathic designation (no identified structural or metabolic cause)
- ✓Current antiepileptic medication regimen and seizure control status
- ✓Seizure frequency and last seizure date if documented
- ✓Confirmation that seizures are NOT intractable and patient is NOT in status epilepticus
- ✓Type of generalized seizures (absence, myoclonic, tonic-clonic) if documented
Commonly Confused Codes
- •G40.301 — Same type WITH status epilepticus; acute emergency
- •G40.319 — Same type, intractable; drug-resistant form
- •G40.009 — FOCAL idiopathic epilepsy; focal rather than generalized onset
- •G40.409 — Other generalized epilepsy, not intractable; when a specific cause is identified
- •G40.909 — Epilepsy unspecified; too nonspecific when generalized type is documented