The short answer
C/O means “care of.” It shows that a letter is for one person but is being delivered through someone else’s address, such as a friend’s home, a business, or a lawyer’s office. Write the recipient’s name on the first line, C/O and the host’s name on the second, then the street address and the city, state, and ZIP Code. USPS’s own example reads JOHN DOE, then C/O ROBERT SMITH, then 123 APPLE WAY.
What c/o means on an envelope
C/O is short for “care of,” sometimes written “in care of.” The name on the first line is the intended recipient. The name after C/O is the person, family, or organization whose address the letter is passing through, usually because the recipient doesn’t live or work there permanently.
USPS uses the format itself. The Domestic Mail Manual shows it for families on rural routes who share one mailbox but have different street addresses, and USPS’s military mail guidance uses a C/O line for mail sent to a service member’s dependents.
Common uses include a guest staying in someone else’s home, a student living with a relative, a client reached through a lawyer or agent, mail for a child sent through a parent, and someone receiving mail at a business that isn’t their employer.
How to write a c/o address
Keep the C/O line above the street address. USPS delivers to the address on the line immediately above the city, state, and ZIP Code, so only the delivery address should sit there. Capital letters without punctuation match USPS’s preferred style, and USPS’s own examples write the line as C/O followed by the host’s name.
- Recipient line: the full name of the person the letter is for.
- Care-of line: C/O followed by the name of the resident, family, or business at the address.
- Delivery address line: the street number and name with any apartment or suite number, or a PO Box.
- Last line: city, two-letter state abbreviation, and ZIP Code.
C/O address examples
These examples use placeholder names and addresses. Each row shows the lines above the city, state, and ZIP Code, in order from the top.
| Situation | Line 1 | Line 2 | Delivery address line |
|---|---|---|---|
| Guest at a friend’s home | ELENA PARK | C/O DAVID KIM | 19 BIRCH LN |
| Child at a parent’s address | MAYA BROOKS | C/O LISA BROOKS | 48 HARBOR VIEW DR APT 3 |
| Client reached through a law office | MARIA GOMEZ | C/O LAW OFFICE OF J PATEL | 200 CENTER ST STE 400 |
| Person using a business’s address | ALEX REED | C/O NORTHWIND STUDIO | 75 MAIN ST STE 210 |
| Shared rural mailbox (USPS’s example) | JOHN DOE | C/O ROBERT SMITH | 123 APPLE WAY |
| Military dependent (USPS’s format) | Dependent’s full name with middle name or initial | C/O and a full name (first, middle name or initial, last) | UNIT, PSC, or similar number and box number, then APO or FPO with AA, AE, or AP and the ZIP Code |
C/O vs. ATTN: which should you use?
Use ATTN when the organization is the addressee and you want the letter routed to a particular person or department inside it. Use C/O when the person is the addressee and the household or organization is only receiving the letter on their behalf.
The line order differs too. Publication 28 places the attention line above the business name, while a care-of line sits below the recipient’s name. Either way, the Domestic Mail Manual says mail addressed to a person at an organization’s address is delivered to the organization. For an employee at their own workplace, ATTN, or simply the person’s name above the company name, is the clearer choice.
| Question | ATTN | C/O |
|---|---|---|
| Who the letter is for | The organization, directed to a person or department | The named person, who gets mail through someone else |
| Line order | ATTN MARIA LOPEZ, then BRIGHT HARBOR DENTAL | ALEX REED, then C/O NORTHWIND STUDIO |
| Typical use | An employee, office, or department at their own workplace | A guest, client, child, or anyone without their own mail at that address |
Does USPS need the c/o name to deliver?
USPS routes mail by the delivery address and ZIP Code. The address block must start with the recipient’s name or another identification, and unless the addressee has given a contrary order, mail is delivered as addressed. The Domestic Mail Manual makes the care-of format mandatory in one published case: rural customers with different primary addresses who keep sharing a single mailbox.
Outside that case, USPS doesn’t publish a general rule that a guest’s mail must carry a C/O line. The line mostly helps the people at the address: it tells them who the letter is for and why it came to their door. A household or front desk that doesn’t recognize a name may not know what to do with the letter.
Hotels and schools have a specific rule. Mail addressed to a person at a hotel, school, or similar place is delivered to that institution, and if the person has left, the institution must redirect it to a known current address or return it to the Post Office.
Certified Mail and signatures when you send c/o
If a particular person needs to sign, a care-of address can work against you. For Certified Mail and other signature services without Restricted Delivery, the Domestic Mail Manual allows mail addressed to a person at a hotel, apartment house, or similar place to be delivered to anyone who usually receives mail for that location.
Restricted Delivery limits delivery to the addressee or an authorized agent, but the same manual says either person may sign for mail addressed to one person in care of another, and that mail for minors may be delivered to their parents or guardians. If a signature matters for a legal or business deadline, confirm the required method and address with whoever sets the requirement; this guide isn’t legal advice.
Forwarding, returns, and temporary c/o addresses
A care-of address works only while the host is still there and willing to pass the mail along. Before you mail, confirm the address with the recipient, especially after a short stay or a move. If USPS can’t deliver the letter, it uses your return address to send it back, so always include one.
Mail for someone who has died follows its own rule: anyone who would normally receive that person’s mail at the address may receive it, and it can be forwarded to an executor or administrator if an order is filed at the Post Office. Writing to the estate in care of the executor, at the executor’s own address, is another option.
Adding a care-of line when you mail through IRIS
IRIS’s letter form has one Name or company field (up to 40 characters), a Street address field, and an optional Apt, suite, unit field. There’s no separate care-of line. If you need one, put it in the name field, such as ELENA PARK C/O DAVID KIM, and keep it within the character limit. Don’t put C/O in the Apt, suite, unit field, which is meant for an apartment or suite number.
That places the care-of note on the same line as the name rather than on a line of its own as in USPS’s examples. If a separate line matters or the names are too long, address the letter to the host and name the recipient at the top of the letter itself. Review both addresses before checkout. A one-page black-and-white letter costs $3.20 with First-Class postage included, and IRIS mails to US addresses only.
Sources & further reading
Product details checked against the IRIS API contract when this article was published. Platform references can change; consult the linked documentation when implementing.
- USPS Domestic Mail Manual 508: Recipient services
- USPS Domestic Mail Manual 602: Addressing
- USPS Publication 28, 212: Format
- USPS Publication 28, 214: Attention line
- USPS Publication 28, 341: Sample business address format
- USPS FAQ: How do I address military mail?
- USPS Postal Explorer: Addressing Your Mail
Published by IRIS Postal Forms, operated by Great Lakes Computing Office LLC. Send a correction.