Sales Tax Lookup by ZIP Code

## The Sales Tax Patchwork

The United States has no national sales tax. Instead, sales tax is levied at the state, county, city, and sometimes special district level. The result is over **13,000** distinct tax jurisdictions.

## State Sales Tax Rates

| Rate Range | States |
|-----------|--------|
| 0% (no sales tax) | AK, DE, MT, NH, OR |
| 4.0-4.5% | CO, AL, GA, HI, NY, WY |
| 5.0-6.0% | Most states |
| 6.5-7.25% | CA (7.25%), IN, MS, RI, TN |

But state rates are just the beginning. Local taxes stack on top.

## Combined Rates by ZIP

Combined state + local rates can exceed 10%:

| ZIP | Location | Combined Rate |
|-----|----------|---------------|
| 98101 | Seattle, WA | 10.25% |
| 70112 | New Orleans, LA | 9.95% |
| 85001 | Phoenix, AZ | 8.60% |
| 90001 | Los Angeles, CA | 9.50% |
| 97201 | Portland, OR | 0.00% |

## Why ZIP Codes Are Insufficient

ZIP codes are not tax jurisdictions. A single ZIP code can span:

- Multiple cities with different city tax rates
- Multiple counties with different county rates
- Special taxing districts (transportation, stadium, tourism)
- Tribal lands with sovereign tax rules

## The Correct Approach

For accurate sales tax calculation:

1. **Geocode** the full delivery address to coordinates
2. **Point-in-polygon** test against tax jurisdiction boundaries
3. **Sum** all applicable taxes (state + county + city + special)
4. **Apply** product-specific exemptions (groceries, clothing, etc.)

Services like Avalara, TaxJar, and Vertex automate this process.

## The Amazon Effect

Since the 2018 Supreme Court decision in *South Dakota v. Wayfair*, online sellers must collect sales tax in states where they have economic nexus — even without physical presence. This has made ZIP-based tax lookup a critical requirement for every e-commerce platform.