Overlapping Boundaries: Treatment and Allocation Process
The use of ZIP+4 area codes in the (county and municipal) tax rate data system is intended to define the smallest area to prevent overlapping boundaries. The 4-digit add-on number identifies a geographic segment within a 5-digit zip code area, such as a city block, office building, or any other area designated by the Postal Service.
In some ZIP+4 area codes there is an overlap of county and municipal boundaries. When this occurs, the statute provides that the lowest rate in the area shall apply. For example, City A has a combined state and city rate of 8%. City B has a combined state and city rate of 7.5%. If the ZIP+4 area code includes both City A and City B, the data system will assign a combined state and city rate of 7.5%. The collections from an area that includes more than one jurisdiction will be allocated between the jurisdictions based upon population.
You may follow the link provided to lookup the ZIP+4 area codes in your city or county and the assigned combined state and local tax rate. You can also contact the Address Management Systems Office of the U.S. Postal Service at (405) 553-6234 for more information about ZIP+4 codes in your area.