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Explainer · US sales tax

Can you look up sales tax by ZIP code?

Only roughly with a 5-digit ZIP: one ZIP code can cross city, county and special district lines, so it can have more than one combined rate. The Washington Department of Revenue puts it plainly: "5-digit ZIP codes do not accurately correspond with tax rates or taxing jurisdictions." A ZIP+4 or, better, the street address identifies the jurisdictions; the Streamlined Sales Tax boundary files map 5- and 9-digit ZIP codes, and in some states addresses, to tax codes.

By New Odyssey · Published · Markdown

Why a ZIP code is not a tax jurisdiction

ZIP codes are USPS mail-delivery codes, not tax boundaries. A city or special district boundary can run through one, so addresses with the same five digits can owe different local rates. Even 9-digit ZIPs are not always enough: Minnesota's rate calculator notes it "may not provide an accurate sales tax rate when a 9-digit zip code crosses city or county boundaries."

Rates themselves vary by state. Texas, for example, imposes a 6.25 percent state rate and local entities can add up to 2 percent, for a maximum combined rate of 8.25 percent.

How the Streamlined Sales Tax files handle it

Each Streamlined member state publishes a boundary file that "generally identifies the tax codes (for each taxing jurisdiction) that apply to an address based on either the 5 or 9-digit zip code", and in some states the actual address, and a rate file with the rate of each tax code. So the precise lookup tries the address first, then the ZIP+4, and falls back to the 5-digit ZIP only when nothing more precise matches; that is the order the Olympus API uses.

In the Olympus API

  • GET /v1/sales-tax/rates/address matches the street address, then ZIP+4, then ZIP, and says which it used (accuracy).
  • GET /v1/sales-tax/rates/zip/{zip} takes a ZIP+4 or 5-digit ZIP; a 5-digit ZIP that spans several jurisdiction sets is answered as ambiguous, with every candidate, not one guessed rate.
  • Published states: CT, DC, GA, IA, IL, IN, KY, MA, MD, ME, MI, MN, ND, NE, NJ, NV, OH, OK, PA, RI, SD, TN, UT, VT, WI, WV, WY. Other states, including Texas, are answered as unsupported. It is a published-rate lookup, not a tax calculation; see Is there an API for sales tax rates by address?.

Questions

Is sales tax based on ZIP code?

No. It is based on the taxing jurisdictions (state, county, city, special districts) at the location, and a ZIP code can span several of them.

How do I find the exact sales tax rate for an address?

Use the state's address-level or ZIP+4 lookup, or in Streamlined member states the SST boundary and rate files, and add up the rates of every jurisdiction that applies on the date of the sale.

Sources