ZIP Code Sales Tax API

Look up sales tax rates by ZIP code with jurisdiction-level accuracy. Our API resolves the fundamental challenge of ZIP codes spanning multiple tax jurisdictions.

Why ZIP Code Tax Lookup Is Hard

ZIP codes were designed by the US Postal Service for efficient mail delivery -- not for identifying tax jurisdictions. This creates a fundamental mismatch that causes errors in naive ZIP-based tax calculations:

  • 1.ZIP codes cross county lines. Over 10% of US ZIP codes span two or more counties, each potentially with different tax rates.
  • 2.ZIP codes cross city boundaries. A ZIP code may include addresses inside and outside city limits, with different applicable city taxes.
  • 3.Special districts don't follow ZIP boundaries. Transit authorities, improvement districts, and other special taxing districts have boundaries that rarely align with ZIP codes.

The result: using a simple ZIP-to-rate lookup table will produce incorrect rates for a significant percentage of transactions, exposing businesses to compliance risk and potential audits.

How Our API Handles It Correctly

SalesTaxAPI uses a multi-layered resolution pipeline to return the most accurate rate for any ZIP code:

Step 1

ZIP Resolution

Map ZIP to county FIPS using HUD crosswalk data, prioritizing the highest-ratio county assignment.

Step 2

Rate Lookup

Query normalized tax rate data using the resolved FIPS code for precise jurisdiction matching.

Step 3

Confidence Scoring

Return a confidence score so your application can flag ambiguous lookups for manual review if needed.

Example Request

GETRequest
curl -H "Authorization: Bearer YOUR_API_KEY" \
  "https://salestaxapi.io/api/rates?zip=84043"
200Response
{
  "success": true,
  "data": {
    "state": "UT",
    "zip": "84043",
    "total_rate": 0.0725,
    "breakdown": {
      "state_rate": 0.0485,
      "county_rate": 0.014,
      "city_rate": 0.01,
      "district_rate": 0
    },
    "county": "Utah County",
    "confidence": 0.98,
    "last_updated": "2026-01-15"
  }
}

Explore State-Level Rates

California →Washington →Colorado →Louisiana →New York →

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Frequently Asked Questions

Why is ZIP code sales tax lookup difficult?
ZIP codes were designed for mail delivery, not tax jurisdictions. A single ZIP code can span multiple counties, cities, and special districts, each with different tax rates. Our API uses FIPS-based jurisdiction mapping to resolve this ambiguity.
How does the API handle ZIP codes that cross jurisdictions?
The API uses a multi-step resolution process: it maps the ZIP code to county FIPS codes using HUD crosswalk data, then returns the rate for the primary jurisdiction along with a confidence score indicating matching accuracy.
What is the confidence score?
The confidence score (0.0 to 1.0) indicates how reliably the ZIP code maps to a single tax jurisdiction. A score of 1.0 means the ZIP falls entirely within one jurisdiction. Lower scores indicate the ZIP spans multiple jurisdictions.
Can I look up rates for any US ZIP code?
Yes. The API covers all active US ZIP codes across all 50 states, including ZIP codes in states with no sales tax (which return a 0% rate).