What Is Zip+4? (All You Need to Know)

Anyone who’s mailed a letter knows there are certain pieces of information you need to include when addressing an envelope- name, street address, city, state, and a 5-digit ZIP code are all essential.

However, have you ever seen a ZIP code with 4 extra digits on the end of it? They’re certainly less common, but they can be very useful when mailing. In this article, we’ll share everything you need to know about ZIP +4 codes!

What Is Zip+4 In [currentyear]?

A ZIP +4 code represents a very specific postal delivery area contained within a 5-digit ZIP code. In some cases, this area represents as few as 5-10 houses or a single floor in a high-rise building. As a result, including these additional 4 digits may speed up mail delivery 1 to 2 days in [currentyear].

You probably still have a lot of questions about ZIP +4 codes, so check out our guide to get all the answers you need!

What Is the Meaning of ZIP + 4?

To understand what a ZIP +4 code means, you first need to know what a ZIP code is.

USPS introduced ZIP codes (short for Zone Improvement Plan) in 1963 as a way of making it easier to ship letters and packages across the country.

Essentially, these 5-digit numbers helped divide the country into different “zones” by providing information about the national area and the destination Post Office/delivery area.

This system worked quite well for a while (and is still in use today), but as the US population increased and scattered, it became necessary to expand on the system.

That’s why USPS introduced ZIP +4 codes in 1983.

These numbers are also called “plus-four codes”, “add-on codes”, or “add-ons,” and represent specific delivery routes within delivery areas.

For example, the 6th and 7th digits denote a specific street or large building.

However, the 8th and 9th digits state which side of the street the address is on or even a specific floor of a large building the mail is going to.

Should I Use a ZIP + 4 Code?

If you have th ZIP+4 code available for your recipient, go ahead and use it.

However, USPS does not require it in most cases, and your mail will get to its destination just fine if you don’t include the additional 4 digits to the main ZIP code. 

There are a couple of instances where USPS does require senders to include the additional 4 digits.

First, the extra digits are required in the return address of mail on which postage is paid with pre-canceled stamps or with a company permit imprint.

They are also required in the sender’s return address on Periodicals mail when “Address Service Requested” is specified.

Finally, the extra 4 digits must be included in the return address of official mail (also known as penalty mail).

Does ZIP + 4 Speed up Mail?

Does ZIP + 4 Speed up Mail? USPS

Adding the additional 4 digits to the ZIP code can significantly increase the speed and accuracy with which your mailpiece is delivered.

In some cases, it may speed up the delivery process by one or two days.

While a standard 5-digit ZIP code denotes which post office the mail needs to go to, the ZIP +4 tells USPS workers which street, which side of the street, and which floor to deliver mail to.

A good analogy for understanding why the extra 4 digits increase delivery speeds so much is to think about a baseball stadium.

Including only the ZIP code is like knowing you need to go to Dodger Stadium, but not knowing where you need to sit.

Adding the additional 4 digits is like having a ticket with your section and seat number on it.

Unsurprisingly, finding where to sit will be a lot faster in the second scenario because you have all the information you need. It works the same way with ZIP +4 codes.

How Do I Write a ZIP +4 Code?

When using a ZIP +4 code, first write the 5-digit ZIP code. Add a hyphen (or dash) after the last digit and then write the 4 additional digits.

How Do I Find My ZIP +4?

Use USPS’ online ZIP code lookup tool to find your ZIP+4 code. You can search by address, city, and state, or by ZIP code.

Even if you think you know your +4 code, it’s worth double-checking.

Unlike 5-digit ZIP codes that change infrequently, +4 codes can change as frequently as once a month, based on things like how many postal employees are working and who’s on which route.

While most addresses will already have a ZIP +4 code, USPS does give businesses the option of applying for a 4-digit ZIP code addendum for their Business Reply Mail.

If you’re a business and need to apply for a ZIP +4 code, you can apply through the USPS website.

What Are the Benefits of ZIP +4 Codes?

While optional, using a ZIP+4 code offers a few benefits.

For one, they require address validation. That means that if an address has a ZIP +4 code attached to it, you know for sure that an address is real.

This benefit is particularly important for businesses sending out a lot of packages.

Another benefit is that using the additional 4 digits may increase the delivery speed of your mail by 1 to 2 days.

To know more, you can also read our posts on what is invalid USPS address, does USPS ship to Singapore, and USPS 2 day shipping.


While less common than standard 5-digit ZIP codes, ZIP +4 codes can be incredibly helpful in getting your mail delivered quickly and accurately.

Sure, it may take a bit of extra work to look up the code and write the numbers on the envelope, but gaining 1 to 2 days in delivery time is well worth it.

Photo of author

Marques Thomas

Marques Thomas graduated with a MBA in 2011. Since then, Marques has worked in the retail and consumer service industry as a manager, advisor, and marketer. Marques is also the head writer and founder of QuerySprout.com.

Leave a Comment