* up-to-date (hyphenated)
* up to date (two words)
Both spellings are correct, but "up-to-date" is more common when used as an adjective, while "up to date" is more common when used as an adverbial phrase.
For example:
* Adjective: "I have an up-to-date list of all the attendees."
* Adverbial phrase: "Make sure your information is up to date."