get_enrollment

Get Enrollment

What it answers

Returns CMS monthly enrollment for a Medicare Advantage plan or contract: the member count, the trend over time, and, at contract level, the MA-only vs Part-D split, plus org/parent and plan type. Filter by contract_id (required) + optional plan_id (plan grain vs contract total), and optional year ('2024') or month ('2024-03'); with neither, returns the latest month plus a trailing 13-month trend. Monthly coverage back to 2006. Every row carries the year-over-year change (yoy_change / yoy_pct) vs the same month one year earlier; plan rows carry the plan's SNP class (snp_type) when applicable.

RETURNS a detail payload, not a bare count: value.summary (latest_month, latest_enrollment, yoy_change / yoy_pct, ma_only_count / part_d_count, trend min/max and change over the window), value.months (the per-month trend rows), value.row_counts (matched / returned / truncated / limit) and value.query (the filters actually applied). `limit` bounds the trend rows returned (default 13 months, max 2000); a truncated list always carries a caveat.

Enrollment is the SPINE every other MA metric joins to (per-member, share-weighted). SUPPRESSION is honest: CMS redacts cells under 11 enrollees, which come back as count=null with a [lower, upper] bound and suppression_reason='redacted_small_cell', never a zero, and the suppression caveat fires only when a returned month is actually redacted. A contract id that does not exist returns found=false with a not_found_reason, never a suppression story.

Pair with get_plan_payment / get_mlr / get_pbp_benefit to weight or normalize by members. SOURCE: CMS Monthly Enrollment by Plan / by Contract.

Inputs

contract_id

string · required

limit

integer · optional

month

string · optional

plan_id

string · optional

year

integer · optional

Call it

From an agent: connect the Vlada MCP once (one click for Claude, ChatGPT, Cursor, VS Code) and ask in plain English; the agent selects get_enrollment when the question fits. From code: the same tool over REST with an API key. The schema endpoint needs no key.

curl -X POST https://api.vladahealth.com/v1/tools/get_enrollment \
  -H "Authorization: Bearer $VLADA_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"contract_id":"<contract_id>"}'

curl https://api.vladahealth.com/v1/tools/get_enrollment/schema      # the JSON schema, no auth
# MCP endpoint (Streamable HTTP): https://mcp.vladahealth.com/mcp

What comes back

Typed rows plus provenance on every answer: the public source file, its vintage, the methodology, and a response_hash you can replay. Prove and replay tools turn any number into a re-runnable receipt. A number the data cannot support comes back as “not in the data”, never as zero.

Sources behind it

medicare_silver.enrollment_monthly_plan
medicare_silver.monthly_contract_enrollment_summary

tables: medicare_silver.enrollment_monthly_plan · medicare_silver.monthly_contract_enrollment_summary

Known limits

Cells under 11 enrollees are CMS-redacted: count=null with a [lower, upper] bound and suppression_reason='redacted_small_cell'.
MA-only vs Part-D split is contract-level only (omit plan_id to get it).
County / market-share grain lives in enrollment_monthly_county (612M rows); this tool serves plan + contract totals.

As of the 2026-09-19 build of the served surface · machine-readable catalog · the live server may run a different version; the schema endpoint above is authoritative for what is deployed.