ZIP+4 adds four digits to a five-digit US ZIP code. The extra digits identify a smaller delivery segment, such as a building, a floor, or a block.
What it improves
ZIP+4 can speed sorting and reduce ambiguity for high-volume mail. It is not required for most consumer addresses, and many people do not know their own ZIP+4.
How to collect it
If you ask for it, label the field “ZIP+4 (optional)” and accept both 12345 and 12345-6789. Do not reject a five-digit ZIP because the extra four digits are missing.
Testing note
Store the value as text so the hyphen and leading zeros survive. Test the export to CSV and the round trip back into the form.
Questions
- For most consumer forms, no. It is optional and often unknown to the user.
- No. It narrows the delivery segment inside the existing ZIP area.
Is ZIP+4 required?+
Does ZIP+4 change the city?+
Examples are synthetic. Do not use a generated address for identity checks, account registration, or delivery.