Check in vs. check-in

Question:

In the following sentence, what is the correct way to write check in? Do I need a hyphen?

• At check-in, the client realized that he did not have his travel information.

Answer:

In your sentence, the compound word check-in is being used as a noun denoting the action of registering one's arrival. In English, there are three ways to spell compound words: as two separate words (e.g. on line), with a hyphen (e.g. on-line) or as a single word (e.g. online). Always consult your dictionary to verify the spelling of a compound, as there is no set rule. Most sources prefer the hyphenated spelling for check-in (when used as a noun or adjective).

Note that if the compound word in question is a verb phrase, such as check in or check over, you must write these compounds as two separate words:

• Clients often try to check in and then realize that they do not have their travel information.
• The student should check over his work (or check his work over) before handing it in.

But when check-in is used as an adjective, don't forget to use a hyphen:

• check-in desk
• check-in agent
• check-in area