Why localities exist Copy link
The cost of delivering care varies across the country, so Medicare divides it into payment localities and gives each one work, practice-expense, and malpractice GPCIs. Those indexes scale a code's national RVUs up or down, which is why the same code pays different amounts in different localities.
How ZIP codes map to localities Copy link
CMS publishes a ZIP Code to Carrier Locality File that assigns each ZIP to a MAC and locality. Postal ZIP boundaries don't line up perfectly with locality boundaries, so a small number of ZIP codes span more than one locality. CMS flags those ZIPs, and placing an address in one of them takes the full nine-digit ZIP+4. Every other ZIP resolves exactly from its five digits.
Resolving an ambiguous ZIP Copy link
For a ZIP that spans localities, an amount picked from the five-digit ZIP alone can be wrong. A careful lookup names the locality CMS lists for the five-digit ZIP, marks it unconfirmed, and asks for the ZIP+4. The crosswalk is versioned by release, so a historical lookup maps a ZIP the way CMS mapped it at the time. Resolve your own ZIP in the locality directory.
Find a ZIP’s payment locality and GPCIs Copy link
Enter the ZIP where the service was performed. A ZIP that spans localities is named as split, never placed in one.
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ZIP 60657 · Q4 2026 release
ZIP 60657 is in the Chicago payment locality (MAC 06102, locality 16).
- Work GPCI
- 1.007
- Practice expense GPCI
- 1.005
- Malpractice GPCI
- 2.295
See Chicago’s amounts and ZIPs
Each GPCI multiplies its RVU before the conversion factor; 1.000 is the national baseline. The work GPCI shown is the one CMS pays with, floor included.
Frequently asked Copy link
What is the difference between a MAC and a locality?
A MAC (Medicare Administrative Contractor) is the company that processes Medicare claims for a region; a locality is a pricing area within that region. Together, the MAC and the locality number identify one set of GPCIs.
Can one ZIP code be in two localities?
Yes. A small share of ZIP codes span more than one locality. CMS flags them in the crosswalk, and they need the full ZIP+4 to resolve to a single locality.
Do locality assignments change?
They can change between releases. Because the crosswalk is versioned, a ZIP resolves the way it was mapped in the release you are looking at.
Sources Copy link
Written from primary CMS sources—see how we source, compute, and verify everything on this site.
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