# Why can't I rely solely on ZIP Code rate tables for tax calculations?

Source: https://developer.avalara.com/address-validation/ofs5203512546562/

# Why can't I rely solely on ZIP Code rate tables for tax calculations?

There are a few reasons why you shouldn't rely on ZIP Codes:

-   ZIP Codes are too broad for tax determination because the USPS sets the zones for mail delivery.

-   State and local tax authorities often use other criteria for bounding their tax jurisdictions, such as a special stadium or restaurant tax district.

-   ZIP Codes can’t correctly handle transactions in states that have mixed sourcing, such as California and Texas. This means that the origin address allocates a portion of the tax and the destination address allocates the other portion.