What Is Zip+4 In 2024? (How It Works, Meaning + FAQs)

Anyone who‘s ever mailed a letter knows you need to include the recipient‘s name, street address, city, state and 5-digit ZIP code. But you may have also noticed some addresses have an expanded code with four extra digits at the end. So what do these additional ZIP+4 digits mean and should you be using them?

A Brief History of ZIP+4 Codes

To understand ZIP+4 codes, you first need to know what ZIP codes are. ZIP codes were introduced by the United States Postal Service (USPS) back in 1963 to help automate, track and speed up mail delivery across the country.

These 5-digit codes are short for "Zone Improvement Plan" and designate postal delivery areas related to cities, neighborhoods or groups of addresses. Using ZIP codes allows postal workers to route mail more accurately by specifying which processing facilities and delivery routes it needs to go through.

{{Image here showing how ZIP codes map to geographic areas and postal routes}}

As more addresses were added over the next decades, USPS found ZIP codes alone were no longer specific enough for efficient routing in dense urban areas. So in 1983, it introduced the +4 extension to target small geographic delivery segments.

Initially these add-on codes were optional. But by 1994 approximately 90% of addresses were assigned an extended ZIP+4 code.

How Do ZIP+4 Codes Work?

The first 5 digits of a ZIP+4 code indicate the standard postal delivery area, like a ZIP code does on its own.

But the additional four digits then zero in further:

• Digit 6 – Specifies range of street addresses or a single large building
• Digit 7 – Specifies which side of a street or which building entrance
• Digits 8-9 – Denotes a specific floor, individual address or even which postal carrier serves that segment

So it essentially breaks down areas within a ZIP code into smaller, more precise geographic units for delivery.

The processing machines USPS utilizes are able to detect these extended codes and automatically route packages. Skipping manual sorting and handling when possible gets mail to its destination significantly quicker.

Benefits of Using ZIP+4 Codes

Including the full ZIP+4 provides some useful benefits:

• Faster mail delivery – USPS statistics show on average 1-2 day faster
  • Complex routes see up to 3 day improvements in one study
• Fewer undeliverable pieces – Prevents improper delivery when street address is unclear
• Free address verification – Confirms residence exists when assigned ZIP+4
• Better mail tracking – Follow path and progress closely when codes are scanned
• Improved targeted marketing results – Connect mailing lists with geographic and demographic data

According to USPS, approximately 8% of mail today still lacks the full ZIP+4 extension.

As more senders adopt the practice, overall postal infrastructure and efficiencies are expected to continue advancing. Properly used, these granular delivery codes help optimize logistics.

{{Table or chart showing effects of ZIP+4 usage}}

When Is ZIP+4 Required?

USPS requires use of the full ZIP+4 code only for certain types of return mail:

• Business Reply Mail
• Official government penalty mail
• Periodicals mailings with address correction requested

So including it in you or your business‘s return address is important for compliance and optimal handling.

But for sending outbound mail, parcels or correspondence, the extended code remains optional. USPS leaves it up those sending mail to decide if enjoying faster delivery times is useful.

How To Find and Use Complete ZIP+4 Codes

Looking up the +4 extension for an address is simple:

• Check recent postal mail – Already included on most statements or letters
• Call your local Post Office or processing center
• Use USPS‘s Online Lookup Tool

To use an extended ZIP+4 code:

1. Write out the 5 digit ZIP code
2. Add a hyphen (-)
3. Include the four additional digits

Proper formatting is essential for machines to detect and route using the full code.

So a completed ZIP+4 code would look like: 10101-0011

Tips For Using ZIP+4

For both residential and business mailers, be sure to:

• Always include ZIP+4 whenever available – Speeds up delivery
• Double check codes using USPS‘s tool – Adjustments happen
• Print clearly and use proper formatting – Ensure machines read correctly

Businesses specifically should also:

• Integrate updated ZIP+4 data into customer contact lists and address databases
• Obtain unique ZIP+4 for Business Reply Mail for optimal inbound processing

Leverage free address verification and faster delivery USPS offers with ZIP+4 whenever possible. Notify senders falling back to 5-digit ZIP when your +4 code changes.

And remember these expanded codes directly route to a single mail carrier – so leave them a nice holiday tip!

Conclusion

A ZIP+4 code appends an extended series of digits to standard 5-number ZIP codes used in US mailing addresses. Introduced back in 1983, it identifies small geographic delivery segments for more precise postal logistics.

Including the full ZIP+4 can speed up a mailpiece‘s transit by 1-2 days on average. It also improves deliverability and confirms destination addresses.

While optional in most cases, using ZIP+4 offers multiple mail processing and tracking advantages for both residential and business mailers. USPS provides access to these extended codes for free online.

So next time you sit down to address some letters or ship a package, be sure to look up and use the receiver‘s full ZIP+4 whenever possible!