Whether you’ve just moved into your first apartment in Seattle or are relocating to a new rental in Austin, you might have noticed four extra numbers at the end of a ZIP code. These ZIP+4 codes help pinpoint specific locations within a ZIP code, improving mail accuracy and delivery speed. But do you really need to use them? And how do they work? Here’s what you need to know.
How do ZIP codes work and why ZIP+4 was added
ZIP codes were introduced in 1963 to improve mail delivery efficiency. Each digit has geographic significance:
- The first number (0-9) represents a broad U.S. region, starting at 0 in the East and increasing to 9 on the West Coast.
- The next two numbers narrow it down to a specific area, like a city or town.
- The last two digits identify an individual post office or delivery zone.
By 1983, as cities grew and mail volume increased, the five-digit system needed more precision. The USPS introduced ZIP+4 codes, an extension that identifies exact buildings, streets, or even specific apartments within a ZIP code.
Why renters should use a ZIP+4 code
If you’re renting, using the correct ZIP+4 code can help with:
- Ensuring mail reaches your specific unit – Especially in apartment buildings where multiple units share the same ZIP code.
- Faster deliveries for online orders – ZIP+4 codes help USPS sort packages more efficiently, potentially reducing shipping times.
- Avoiding missed bills or documents – Important mail like lease agreements, utility bills, and credit cards are less likely to be misdelivered.
- Setting up utilities and renter’s insurance – Some service providers use ZIP+4 codes for address verification.
How to write a ZIP+4 code correctly
When including a ZIP+4 code in your address, it’s important to format your address properly to ensure smooth processing by the USPS. The extra four-digit extension should be written after the standard five-digit ZIP code, separated by a hyphen.
Correct ZIP+4 Format:1234 Main Street
Seattle, WA 98101-1234
Always separate the five-digit ZIP code from the four-digit extension with a hyphen.
How can I find my ZIP+4 code?
As a renter, ensuring you use the correct ZIP+4 code can save you headaches down the line. Here’s how to find yours:
- Use an online ZIP+4 lookup tool to get the exact code for your apartment address.
- Check the USPS ZIP Code Lookup tool, which provides the most up-to-date information.
- Ask your landlord or property manager—they often have the correct ZIP+4 for the building.
Do ZIP+4 codes change?
Yes, ZIP+4 codes can change over time due to:
- New apartment buildings or changes in delivery routes.
- Reorganization of postal service areas to manage mail volume.
- Adjustments based on staffing and logistics at local post offices.
If you’ve recently moved or switched apartments within the same building, double-check your ZIP+4 code to avoid mail mix-ups.
ZIP+4 code FAQs: Extra questions you might have
Do I have to use a ZIP+4 code when mailing something?
No, ZIP+4 codes are optional for most mail, but using them can help ensure faster and more accurate delivery. They are especially useful in high-density areas like apartment buildings and business districts.
Can two addresses have the same ZIP+4 code?
Yes, a ZIP+4 code can cover multiple addresses within the same building or area. However, it still provides a more precise location than a standard five-digit ZIP code.
Why do some websites automatically add a ZIP+4 code to my address?
Many online forms and shipping services use address validation tools that pull ZIP+4 codes from USPS databases. This ensures the most accurate delivery information is used for orders, billing, and service verification.
Does every apartment in a complex have a different ZIP+4 code?
Not necessarily. Some apartment buildings assign different ZIP+4 codes to individual units, while others share a single ZIP+4 for the entire complex or specific sections.
How often do ZIP+4 codes change?
ZIP+4 codes can change due to postal route adjustments, new developments, or reorganizations within the USPS. It’s always a good idea to check your ZIP+4 code when moving or updating your address.
Can ZIP+4 codes help with emergency services?
Yes, ZIP+4 codes can assist in more precise location tracking, which may be useful for emergency response teams in large buildings or complex addresses. However, they are not a replacement for full address details in emergency situations.
