CMS Marketplace API

Path A data source — 28 federal marketplace states

Overview

The Centers for Medicare & Medicaid Services (CMS) Marketplace API provides real-time plan data, eligibility estimates, and subsidized pricing for all states that use the federal Healthcare.gov marketplace.

Base URL: https://marketplace.api.healthcare.gov/api/v1Authentication: API key (free, request from CMS) Coverage: 28 states + seasonal updates

Endpoints Used

Endpoint	Method	Purpose
/counties/by/zip/{zip}	GET	Resolve zip → county FIPS code
/households/eligibility/estimates	POST	APTC amount + CSR level
/plans/search	POST	Silver plans with subsidized pricing

Key Behaviors

• Medicaid flag: Returns is_medicaid_chip: true for incomes below ~138% FPL. No APTC or CSR returned. We handle this by re-querying above threshold and recalculating APTC.
• CSR variants: Automatically returns CSR-enhanced benefits when income qualifies. Plan names change (e.g., "Silver 5900" → "Silver 0 Medical Deductible").
• APTC is pre-calculated: The API does the SLCSP lookup and IRS formula internally. We override with our own calculation for Medicaid-income cases.

States Covered

AL, AK, AZ, AR, DE, FL, GA, HI, IN, IA, KS, LA, MI, MS, MO, MT, NE, NH, NC, ND, OH, OK, OR, SC, SD, TN, TX, UT, WI, WV, WY

Limitations

• Does not cover state-based marketplace states (CA, NY, NJ, PA, etc.)
• Returns "not a valid marketplace state" for SBE state zips
• API key is rate-limited (exact limits unpublished but generous for demo use)