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ZIP+4 Codes | What are they and How do I find mine?

ZIP+4 Codes are the last 4 digits of a nine-digit ZIP Code. Some people don’t know that zip codes are actually longer than 5 digits. The 9-digit ZIP Code is made of two different parts. The first part is the first five digits of the zip code which indicates the destination post office or delivery area. This is the part of the zip code that everyone is aware of. The last 4 digits of the nine-digit ZIP Code represent a delivery route within a specific delivery area. When you use all 9-digits of full zip code, it assists the USPS in sorting and delivering the mail.

Interested in finding out the ZIP+4 code for a specific address? You can do that now by using our free Zip+4 Lookup Tool.

ZIP+4 Codes

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How do zip codes work and why are there now zip+4 codes?

USPS 5-digit Zip Codes

USPS five-digit zip codes are the zip codes you are familiar with. Examples are 92019 or 84604. The 5 digit zip code most commonly indicates a destination post office.

Here’s how it works:

  • A postal carrier collects your letter from the box along with the rest of the mail and takes it to the post office. There, all of the mail is placed on a truck and taken to a mail processing plant.
  • At the mail processing plant, machines separate mail by shape and size. They also orient the packages so their addresses are right-side up and facing the same direction. Your letter gets its postmark, and machines print cancellation lines across postage stamps to prevent them from being reused.
  • A unique bar code is imprinted on the back of each piece of mail. An optical scanner scans the address, and then a bar code representing the specific address is sprayed on the front of the envelope. If the scanner can't read the address, the letter is manually sorted.
  • Other processing machines read the bar codes and direct the letters into bins based on ZIP codes — this indicates the next processing plant, in the region where the letter will ultimately be delivered. (Each post office is served by a mail processing plant.) From the bins, the letters are sorted into trays by ZIP code and flown or trucked to the next processing.
  • At the final processing plant, sorting machines read the bar codes and sort the letters by carrier and into delivery order for that carrier.
  • The letters are taken to the individual post offices, and the carriers load the trays into their individual vehicles for final delivery.

Zip+4 Codes - 4 extra digits

A ZIP+4 code uses the basic five-digit code plus four additional digits to identify a geographic segment within the five-digit delivery area, such as a city block, a group of apartments, an individual high-volume receiver of mail, a post office box, or a specific delivery route — meaning the actual path the mail truck would travel could have changed.

Because they are based on delivery routes instead of more permanent boundaries, the last 4 digits of a complete ZIP code can change often. Five-digit ZIP codes also change, but they do so infrequently. Not so for ZIP+4. The +4 on a ZIP code can be changed as frequently as once a month, based on things like how many postal employees are working, who is working what route, etc.

A ZIP code is a postal code used by the United States Postal Service (USPS) in a system it introduced in 1963. An extended ZIP+4 code was introduced in 1983 which includes the five digits of the ZIP code, followed by a hyphen and four additional digits that reference a more specific location. However, initial attempts to promote universal use of the new format met with public resistance, and today the +4 code is not required. In general, mail is read by a multiline optical character reader (MLOCR) that almost instantly determines the correct ZIP+4 code from the address — along with the even more specific delivery point — and sprays an Intelligent Mail barcode (IM) on the face of the mail piece that corresponds to 11 digits — nine for the ZIP+4 code and two for the delivery point.