About zip4lookup

Why this exists

The five-digit ZIP code gets mail to a post office. The four digits after the hyphen get it to a specific delivery point — one side of a block, a single building, a run of PO boxes. Those four digits are what USPS bulk postage discounts are priced on, and what most address-validation systems use to confirm a delivery point actually exists.

Finding them for one address should take five seconds and cost nothing. Finding them for forty thousand addresses should be a file upload. Neither of those was true of the tools we could find, so we built this.

Where the data comes from

We do not own the address data and we do not pretend to. It is licensed — from the United States Postal Service and from commercial data providers whose matching engines are certified against USPS standards. What we build is the interface, the caching, the bulk processing, and the tools around it.

That distinction has a practical consequence for you. Our licences restrict what we can pass on, which is why our Terms of Service permit you to use results inside your own business and prohibit reselling them as data. If your business model needs the latter, write to us — it is a different agreement, not an impossible one.

Some of what we layer on top is public and free, and we say which is which rather than implying it is all proprietary:

How we handle the addresses you send us

Most of what passes through this service is other people's addresses, and that shapes how we treat it.

• Results are cached for 30 days so repeat lookups are instant and free. The cache holds postal facts, not a record of who asked.
• Files you upload are deleted after 7 days — long enough to download your results, short enough that we are not sitting on your customer list.
• We do not sell your data, share your uploaded lists, or use them to train models or build any derived product.
• We do not build profiles of the people whose addresses you submit, and our terms prohibit using this service to locate or investigate an individual.

The full detail is in the Privacy Policy, including every retention period. Those numbers are the real ones — they are enforced by scheduled jobs, not by good intentions.

What we are not

• Not the USPS. ZIP Code and ZIP+4 are USPS trademarks. We are independent, and we are not affiliated with, endorsed by, or sponsored by the Postal Service or any government agency. If you are filing a change of address, do it at usps.com — not through any third-party site charging $40 for it, including a hypothetical future version of us.
• Not a people-search service. We look up addresses, not people. Using this to find or investigate an individual is a breach of our terms.
• Not a consumer reporting agency. Our output is not a consumer report and may not be used for credit, employment, insurance, or tenant screening.
• Not a tax engine. We identify taxing jurisdictions at an address. We do not determine what tax is owed on a transaction.

Being honest about accuracy

Addresses change constantly — new construction, renumbering, boundary changes, monthly file updates. No address service is right all the time, and one that claims otherwise is telling you something about itself.

What we do instead is show our work. Every lookup returns a delivery point confirmation code telling you how confident the match is, a vacancy flag, and whether the result came from cache. Where a result is approximate — a ZIP-level tax rate rather than a ZIP+4 one, demographics describing an area rather than a household — the response says so in the payload rather than in the small print. Decisions with money attached deserve to know which kind of answer they are getting.

Contact

legal@zip4lookup.com reaches us for anything: support, billing, privacy requests, security reports, licensing questions, or to tell us something on this site is wrong. We answer privacy requests within 30 days and usually much sooner.

Found a bug or a wrong ZIP code? Tell us. Corrections are the cheapest quality improvement available to a service like this one.