Address Verification

ZIP+4 Codes – The Last 4 Digits of ZIP Code

By 28 April 2024May 23rd, 2024No Comments
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ZIP+4 Code - What is it and the Purpose of Last 4 Digits of ZIP Code:

Zip+4 Code: What is it? And What is the Use of It.

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Imagine you are living in Georgia and want to mail a letter or a postcard to your customer residing in Atlanta. So, Georgia is the first carrier to receive the mail item and does not need to know the exact address for delivery. His only concern is which post office should he forward the letter to – This is where ZIP +4 codes come into action! Let’s start this blog by imagining a scenario!

What is a Zip+4 Code?

A ZIP+4 code is a four-digit postal code used by the United States Postal Service (USPS) that is appended to a five-digit ZIP Code. Zip+4 codes are made up of a 9-digit code, with the first 5 digits representing the standard ZIP code and the last 4 digits identifying a specific group of addresses or a geographic location.

The first 5 digits of a 9-digit ZIP+4 code refer to a specific delivery area, and the additional four digits identify a smaller area within that delivery area. The use of ZIP+4 codes helps the USPS to more efficiently sort and deliver mail to specific addresses.

Usually, the five-digit delivery area is divided into geographic segments, such as a city, street, apartment or complex, or more.

Additionally, Zip+4 codes assist in sorting and delivering mail, speeding up delivery time, decreasing delivery errors, and allowing mailers to qualify for bulk mailing discounts.

We know that you are curious to learn all about Zip+4 codes- Join us as we explore them.

But, before you jump in with us to know the details, let us look a little back in time…..

Let’s start with a journey to the past.

Looking Through a Window Glass of The Past

If you have ever tried sending direct mail to someone, you have likely come across the term ZIP+4 code. The origin of the ZIP code dates back as far as 1963.

It was introduced as a solution to make mail travel faster. During its inception, the ZIP codes only consisted of 5 digits but, as the mail system grew bigger and more complex along with the growing population in the US, the 5-digit ZIP codes were no longer doing the job well enough.

Hence in 1983, the USPS introduced the ZIP+4 codes, which are also known today as “+4 codes,” and the purpose of this ZIP+4 code is simply to add more precision to the standard five-digit ZIP codes.

In a nine-digit full ZIP Code, the first five digits represent the specific delivery area or post office of an address, whereas the last four digits of the ZIP code indicate the delivery area down to a few blocks radius or specific delivery area.

The entire nine-digit ZIP code, in effect, streamlines the delivery process for the USPS and ensures that your direct mail is sent or received with minimal delay. So it doesn’t matter whether you are sending mail or receiving one. It is important to know your ZIP+4 code so that the package can easily be delivered to its destination.

What are the Last 4 Digits of my ZIP code?

Many people are often unaware of their ZIP code’s last four digits, and their number is surprisingly high. Apart from this, most people are unaware of the full 9-digit ZIP code for the direct mails they send out. Although the post can be sent without the ZIP 4 code, it would be considered slow to move along and can take a while before it reaches the recipient.

The ZIP code or Zone Improvement Plan was something the USPS came up with to make the postal service easy and quick across the country. The ZIP codes divide the country into different zones enabling the USPS to accelerate its postal sorting and delivery process effectively. Therefore, it is always best to provide the full 9-digit ZIP code if you want the letter or package delivered sooner rather than later.

The question now becomes how do I find the full ZIP code to the address I want to send a direct mail to? When it comes to businesses that send out regular direct mails to their customers, this question is even more crucial because they often work on deadlines. When working on a deadline, speed is vital, and the post reaches the customers even more urgently.

Hence, businesses must turn to advanced address verification tools like PostGrid that can provide a complete address, including the full 9-digit ZIP codes for your address database. What makes it even better is that you can do this in a matter of seconds, and it only takes you a few clicks.

There is no need for carrying out a ZIP 4 lookup for every address, all you need is a CSV file, and whoosh….you can easily get the data you need with a few clicks.

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Benefits of ZIP+4 Codes

ZIP+4 codes offer many advantages apart from accuracy and fast delivery, including

Better Delivery Routes

USPS always collects resources to create better and faster delivery routes. ZIP+4 codes aid them in this process, ensuring you get your mailers via the best route possible. It lets carriers sort the items faster and get them to their destinations within the estimated arrival times.

In-Depth Address Verification

ZIP+4 codes enable address validation vendors to fetch better results. It lets you cross-reference your database with others, like a GIS (Geographic Information System).

Higher Security

Adding ZIP+4 codes to your delivery addresses reduces the risk of identity theft and other fraud. You can provide detailed information about where your customers love to prevent the mailers from falling into the wrong hands.

More Comprehensive Insights

Organizations can get more accurate data analytics using ZIP+4 codes to improve their marketing efforts and expand their customer base. They can use their audience’s accurate locations to identify geographical patterns. Thus, they can channel their initiatives in the most profitable direction. For example, they can open a franchise where most of their buyers live—to attract more sales.

When it was first launched, the five-digit ZIP code was a revolutionary step for the US postal service. It significantly simplified the way the USPS functioned and streamlined its operations. The ZIP 4 code was brought in later to accommodate the growing population.

However, that’s not all the ZIP 4 code does. According to a recent study by the USPS, about 40 million Americans move every year, that is, 40 million address changes every year and potentially 40 million undelivered letters/packages every year.

Although 40 million may not be the real number of undelivered mailings, it is safe to say that a large number of mailings may not be delivered or shipped to the wrong address if it wasn’t for the ZIP 4 code.

As per the data from USPS, out of a whopping 158 billion mailed items in 2013, only a mere 4.3% of them were marked “Undeliverable as Addressed (UAA).” Had it not been for the ZIP 4 code, this number could have been a lot worse.

The role of the ZIP 4 code doesn’t end there either. It further goes on to boost the delivery speed and accuracy of the USPS mailing significantly. This is evident from the one or two-day deliveries made by the USPS.

But perhaps what can be considered the most significant benefit of the ZIP 4 code, especially for businesses, is that the ZIP+4 codes require address validation. In other words, even if you use a free ZIP program for making a code, you need to standardize and validate the code before it is valid for an address.

In Layman’s terms, an address with a ZIP 4 code can be sure to exist and also be deliverable. And the cherry on top for the businesses using the ZIP+4 code is that they can help with getting your business bulk mailing discounts.

Somehow, for tools like PostGrid- Well, they have a lot to offer in terms of ZIP 4 Codes, such aspects are:

You can easily track all Mail Outs & Deliveries. Businesses can have quality control with a 99.9% address-related error-free rate. Launch triggered mail campaigns. And….more

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How are ZIP Codes Used

The 9-digits full ZIP code works in parts. For example, consider a direct mail is sent to New York City from Dallas, the carrier that first receives your mail from Dallas need not know the exact delivery address of the recipient. The mail first needs to be forwarded to the appropriate mail carrier, which in this case is the state of New York.

Now, here is where the ZIP code comes into the picture for the first time during the travel of your direct mail. As mentioned before, the ZIP codes are assigned to post offices all around the country by USPS, and each post office has at least one ZIP code assigned to it. In case the post office handles postal services to more than one ZIP code, it will have more ZIP codes assigned to it.

The first five digits are used at this stage to ensure that the direct mail is sent to the correct post office. At this stage, there is no point bothering with the ZIP 4 code at this point. Once the direct mail reaches the destined post office, the first 5-digit of the ZIP code becomes practically irrelevant other than cross-checking the address. Once the direct mail is received at the relevant post office, the ZIP 4 codes can then be used to figure out where the mail is delivered. The ZIP 4 code allows assigning the right person for the delivery based on their delivery route, thereby streamlining the entire delivery process.

USPS Five-Digit ZIP Codes

Now that we have an overview of the two parts of the 9-digits ZIP, we can now discuss how exactly the ZIP code helps identify your most accurate location. The best place to start this is the USPS five-digit ZIP codes that we are all familiar with.

Like we discussed before, they are most commonly used to indicate the post office that will take it to its final destination. However, most of us don’t know that each number in the five-digit ZIP code is significant to its destination.

The first digit of your five-digit ZIP code signifies the national area, while the next two digits signify the sectional center or large city post office. The last two digits of the five-digit ZIP code give the associate post office or delivery area, thereby giving the people at USPS a comprehensive idea of the postage destination.

Furthermore, the ZIP codes allow the postal worker to effectively deliver as many postages as he/she can in a day. In essence, you may treat the five-digit ZIP code as the post office’s address, and although some post offices deal with posts with more than one ZIP code, normally, each post office has just one ZIP code.

Do not imagine the ZIP codes as “boundaries,” but rather think of them as delivery routes that are not constrained by any geographic or administrative boundaries. They may cross city, state, or even country lines. In a way, you may even say that they are governed by where the delivery truck goes.

It should come as no surprise to you that there are certain special ones even among ZIP codes. “Military” ZIP codes are one of the special ZIP codes, and they can be used for everything from military bases, domestic or otherwise, to battleships.

These are unique codes and serve a specific purpose of being individualistic from the standard ones to avoid any form of confusion. It is also possible for businesses and organizations to get their own ZIP code due to the high volume of mail they receive every day. This is very practical for both the business and USPS. The business usually has an internal mail department that can presort mail before distributing it inside the company.

Similarly, the direct mails sent out from the company are also presorted. Furthermore, these firms also enjoy the benefit of bulk mailing discounts thanks to their internal mail department.

ZIP+4 Codes - The Last 4 Digits of ZIP Code

If you want your direct mail delivered in the fastest and most accurate way possible, you’ll need to provide the ZIP+4 code and the normal five-digit ZIP. However, the ZIP 4 code is only available for addresses that are standardized and validated to be real.

The ZIP code’s last four digits indicate a very specific delivery route that includes the mail truck’s actual path taken for travel in a single drop-off. Typically this route consists of ten to twenty homes/locations. Sometimes the ZIP 4 codes are also given to PO boxes. They usually get their own ZIP 4 code that more often than not matches the box number.

Since the ZIP+4 code digits are based on delivery routes rather than permanent boundaries, the last 4 digits of ZIP codes can often be subjected to change. Although the five-digit ZIP code also changes from time to time, their changes are far less frequent as compared to the ZIP+4 codes. It is unlikely that the five-digit ZIP code of a place will change while you are still living there as they remain the same for most of the time.

On the other hand, the ZIP 4 code can change much more frequently and may sometimes change once a month based on several factors. These factors include the number of postal employees working, the route taken by the delivery truck, etc.

Full Zip Code Lookup

Businesses who want to optimize their direct mails, whether it be for a campaign or for sending out important documents like bills, need to include a full ZIP code on the posts they send. The full ZIP code of a mailing address ensures that your post reaches its destination quickly and efficiently.

The full mailing ZIP code of an address also offers much higher deliverability because these addresses are standardized and validated to be real. Therefore, the more accurate and efficient your address verification system, the better your direct mailing process will be for your business.

The best way for you to carry out a full zip code lookup for business purposes would be to use advanced address verification tools such as PostGrid. With an API, like PostGrid, you can easily upload your address database, small or big, as a CSV file and you can easily get the verified version of your address database.

Not only does PostGrid verify the address for you against the official postal address database of USPS, but also it fills in missing data, including the full 9-digit zip code for every address. You can even use PostGrid’s Address lookup API to implement an autocomplete feature on your website that would let you type in their address and generate their full address.

The autocomplete feature can come in handy for your other marketing efforts, such as landing pages, by providing a convenient way for the user to type in their details and, in effect, encourages conversions as they make the desired action (Filling the form in this case).

You can take it a step further by fully automating your business’s direct mail management process by using PostGrid’s fully-documented REST API to send out personalized letters, checks, or postcards to your target audience.

You can either send the direct mails on-demand or at scale, depending on your requirements. With a deliverability rate of 99.99%, PostGrid print and mail API automates and optimizes the entire process involved in direct mailing, saving you valuable time and effort, which can now be utilized for the more important aspects of your business.

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ZIP+4 Code Database

You can access the ZIP+4 code data on the USPS website. Also, you may leverage the postal service’s address validation API. The Post Office lists a comprehensive list of advantages and restrictions of using these tools via online articles, You can read those to understand how to use the APIs better.

However, the most reliable way to access the USPS official ZIP+4 database is to associate with a licensed or CASS-certified address verification service, like PostGrid. This data keeps changing almost monthly. Hence, you need a solid partnership to update your mailing addresses frequently. It ensures you don’t encounter any obsolete ZIP codes.

What are the Advantages of ZIP+4 for Business?

Individuals can enjoy multiple benefits with their address data management and shipping process using ZIP+4 codes. 

The following are some notable benefits; 

Faster Deliveries 

Professionals can use ZIP+4 codes to represent different segments of delivery routes within a single block. A simple 9-digit makes it more efficient for the delivery workers to understand the way.

USPS also prefers this format to learn where exactly to deliver the mail. Businesses can use ZIP+4 codes to increase the pace of their processing and delivery times. E-commerce companies can massively benefit from the use of these codes. 

Reduction in Failed Deliveries & Lost Mail

An efficient delivery route also eliminates the possibility of failures. Businesses can reduce the chances of lost mail by following the ZIP+4 format in their shipments. It will also help the postal workers to deliver the mail to the right destination.  

Reduce Your Returned Mail 

An individual must enter a valid address to obtain a ZIP+4 code. They can standardize their addresses according to the USPS address format to ensure smoother deliveries. Standardized addresses always help USPS in reducing returned mail. 

Huge Savings on Bulk Mailings 

USPS provides commercial mailing discounts to people sending at least 50 packages or over 200 pieces of mail. 

Yet, if they use ZIP+4 Codes and Delivery Point Barcodes, USPS can provide additional discounts of up to 5 to 60% on the usual post office prices. It could be a significant savings for businesses sending bulk mail regularly. 

Clean Address Data

A smooth mail or package delivery requires validated, standardized, and corrected addresses. Professionals must ensure the above to obtain a valid ZIP+4 code for their shipment. They can clean their address data by gathering ZIP+4 codes for them. 

Verified addresses are always helpful in removing duplicates and redundancies and merging records. Companies can get rid of every poor data from their database.  

Enhancement in Address Data 

Sometimes, address data could be vague or incomplete. It can reduce the chances of successful deliveries and lead to return mail. 

PostGrid can help businesses to obtain ZIP+4 codes with additional data points about an address. This data can be beneficial in your business intelligence to understand the recipients better. 

Your mail and packages can show up faster with a ZIP+4 code. 

Using USPS ZIP Code Lookup Tool 

One can use the free web-based USPS ZIP Code Lookup Tool to find ZIP+4 codes for different addresses. Here’s how you can use the tool; 

  • Visit the official USPS website and go to the ZIP Code Lookup Tool Page. 
  • Write an address for which you want a ZIP+4 code. Mention the city, state, or ZIP code to refine your search results. 
  • Click the “Find” button to fetch the ZIP+4 aligned with the address. 
  • The tool will provide you with a ZIP+4 code. You will also get additional information, such as the carrier route code, the 5-digit ZIP code, and the delivery point code. 
  • You can download the USPS ZIP+4 Code file to run a batch-processing task. This file contains the entire list of ZIP+4 codes present in America. 

The Story of 5-Digit ZIP Codes: History and Invention

H. Bentley Hahn first proposed the idea of a five-digit code in the 1940s to locate different areas in the country. Germany was also using a similar system during the 40s. 

Hanh realized the existing US postal system needed to be faster and more efficient as a postal inspector. Manual sorting was making the entire infrastructure sluggish and rigid. A new approach was necessary to streamline the sorting and delivery process in the country. 

The ZIP code system was first introduced in 1963 with five-digit codes to locate specific areas. Its first three digits represented a regional sorting area. At the same time, the last two digits represented a particular post office. 

The introduction of the ZIP code system was a revolutionary step in changing the mailing system of the United States. Processes were much faster, more accurate, and more efficient with this new format. 

Postal services became more reliable throughout the nation with precise sorting and routing of mail.  

What is the Difference Between ZIP Codes and Postal Codes?

Many individuals often have misconceptions about the two. They even use the two terms interchangeably. Yet, they must learn about the subtle differences in superior data management. 

This chart will help in understanding these differences; 

Postal Code  ZIP Code 
Country  Rest of the world United States of America 
Length  It can have different lengths depending on the country.  It always has five digits. 
Format  They can be alphanumeric across the world.  There are only numeric values in ZIP codes. 
Use It is a global format for mail delivery and sorting.  People only in the United States can use ZIP codes for mail delivery and sorting. 

People only in the United States can use ZIP codes for mail delivery and sorting. 

The basic functionality of ZIP codes and postal codes are similar. Yet, ZIP codes are only specific to the United States, while postal codes are standard in the rest of the world. 

Importance of ZIP+4 Codes for Business Operations

Business owners should always appreciate the power of ZIP codes. These codes could be beneficial for; 

Targeted Marketing with Geo-Location 

Many firms are using ZIP codes to run targeted marketing campaigns. It helps them to make their advertising efforts relevant to specific geographic demographics, customer behaviors, and local events. 

Preventing Frauds

Many finance companies prefer using ZIP codes as an additional security measure to eliminate fraudulent transactions. They often use ZIP code verification during credit card transactions to verify the identity of the person making the person.  

Segmenting Customers 

ZIP codes are also helping marketing professionals to segment their customers. They can learn the distribution of customers across different zones with ZIP codes. 

It helps them explore various patterns and trends to customize their marketing efforts further. They can launch different offers for each customer segment. 

Regulatory Compliance 

Many industries need the use of ZIP codes for regulatory compliance. For example, financial businesses must use ZIP codes to determine premiums and coverage policies. 

The latest ZIP codes are handy to ensure their data is latest and accurate. They can remain completely compliant with the regulatory guidelines.

Data Quality Management 

Many companies need help with maintaining their address data. ZIP codes could be helpful in data cleansing to ensure the database is clean and accurate. They can compare their data to a trustworthy database (USPS) to find any errors or inconsistencies.

Full ZIP Code Lookup for Offline Communication and Cross-Channel Campaigns

Once you have a full 9-digit ZIP code added to your database's addresses, you can significantly improve your offline communication capabilities. You can further use this data for your cross-channel marketing campaigns. The full zip code lookup can greatly help businesses and marketing domains in many ways.

They also come with certain limitations. Before you can employ advanced automation tools for your business’s offline communication and cross-channel campaigns, you should consider its advantages and disadvantages.

Advantages of Full ZIP Code Lookup for Offline Communication

The shipping quality of the offline communication methods is greatly improved when you carry out a full ZIP code lookup and use the ZIP+4 code, and it ensures the offline communications are delivered in a single drop-off. Another advantage of a ZIP+4 code lookup is that the addresses are subjected to a standardization process.

Then the standardized address is subjected to validation with the official postal address database of USPS. This makes sure the address is deliverable, reduces your return rates, and effectively improves the ROI (Return of investment). 

The USPS encourages using ZIP+4 codes for bulk mailings by offering discounts because the ZIP+4 codes give USPS valuable information that will help them sort through their mail items more efficiently. As a result, the USPS only has to spend minimal resources to mail pieces to their destination.

Offline business communication is thus made not only more time-efficient but also cost-effective. By doing this, companies can optimize their operational expenses and further contribute to a higher ROI.

Another aspect of your offline communication affected by the utilization of full ZIP code lookup is the speed. Throughout this article, we have mentioned many times how the full nine-digit ZIP code enhances the speed of operation and speed of delivery of the post.

The ZIP+4 code enables the USPS to direct mail much faster, which is ideal for businesses that want to send out important documents such as invoices, bills, or bank statements. The documents reach their destination in the shortest possible time and minimize the risk of late delivery, which effectively improves your customer service quality.

Disadvantages of Full ZIP Code Lookup for Offline Communication

Although the full ZIP code lookup tools significantly enrich the customer data and are invaluable in terms of efficiency, there is a risk of it integrating poorly with an automated mail printing and delivery system. Unless the solution of your choice is fully automated, like PostGrid, which allows you to carry out a full ZIP code lookup and have them printed and mailed to the right destinations, you may end up hiring a separate team to handle the offline communications.

Such a measure could affect your budget and keep your staff away from doing the more important work than organizing mail fulfillments. Similarly, not having a fully automated system like PostGrid can become a nightmare if the offline mailings are managed poorly by the team that takes care of them. There will always be the scope of human error in your offline communication system.

Advantages of Full ZIP Code Lookup for Cross-Channel Marketing

Using an advanced bulk address verification tool like PostGrid for a full ZIP code lookup allows you to get a more comprehensive and data-driven idea about the geographic area your target audience lives in. You can use this to collect additional demographic data about the target audience.

Once you get your hands on this type of data, you can then utilize it to learn the average household income, median age, and other such nifty details through governmental bodies' official statistics. This kind of data can be a treasure trove for a capable marketing team. They can use it to come up with personalized advertising for the target audience through numerous marketing channels.

The channel used for the purpose could be anything from billboards to regionally-relevant, personalized postcards. Once you can relate a specific customer or even customer group to their daily route, the marketing team can select the ideal product to be advertised based on the new data obtained.

In effect, a full ZIP code lookup can lead to enhancing the marketing campaigns and their overall quality despite which marketing channel you decide to use. Furthermore, the accuracy of your cross-channel marketing is greatly improved through a full ZIP code lookup.

This can be better utilized by companies or businesses that do not have extensive data on their customers and are constrained by their marketing budget to invest in advanced methods for collecting more data on their leads or customers.

Disadvantages of Full ZIP Code Lookup for Cross-Channel Marketing

As far as cross-channel campaigns are concerned, their effectiveness is to a great extent dependent on automation. The effective implementation of cross-channel is not feasible unless automated to get you the best possible result.

The full ZIP code lookup offered by the USPS is not equipped with the advanced capabilities that are needed for the marketing automation of medium to large-size companies. The USPS services offered for a full ZIP code lookup are pretty rudimentary and with limited data enrichment capabilities.

 For a business, it is highly impractical to use legacy solutions provided by USPS for determining the extended ZIP code of addresses in your database. As a result, your cross-channel marketing campaign may suffer.

Therefore, you need two things to get the desired result from your cross-channel marketing efforts: marketing automation software and an advanced tech solution. This is where an advanced, fully automated print and mail solution like PostGrid comes into the picture.

As tools like PostGrid are advanced and can be integrated into your website using API, it allows for complete automation of your direct mail campaigns. PostGrid’s capability to integrate with your business website along with its superior analytics makes it a one-stop solution for streamlining your cross-channel marketing efforts.


As we're near the conclusion of this article, we find ourselves facing the best way to implement an extended ZIP code lookup for businesses. It is evident that, at a time when the competition is now harder than ever, businesses need to have an edge through reliable methods like cross-channel marketing and even offline communication through posts.

Unlike the use of ZIP+4 codes by individuals or even small-scale businesses, companies with a fairly large address database can not afford to stick with traditional solutions.

Traditional solutions like USPS extended ZIP code lookup are not the right match for businesses regardless of size. It is, therefore, necessary for businesses to adopt a more simplified, accurate, and well-organized solution.

Even partial automation, including address verification, may not get you the results you hope for. By using advanced tools, like PostGrid, you can streamline the entire process of cross-channel marketing. It can also save you valuable resources, which you can use for the more important goal of growing your business.

Lastly, Our award-winning direct mail services provide you with additional capacity if a low deliverability rate is an issue. Our team has designed PostGrid so that anyone can integrate it easily with all their existing data sources like system solutions, CRMs, web- applications, and so on.

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