You should really only use this form in spoken, informal English. Maybe in a whatsapp message, too. Where I come from (London) it's quite common to use "cuz" in conversations, it's faster to say and most people love that! I recommend never using it in written form, it's more like an unofficial abbreviation than a real 'word'.

'Cuz' is not an actual word - it is just a reduced form of the way we sometimes say the word 'because'. If it feels natural to you, you can SAY 'cuz' whenever you like in informal contexts - it's just an extreme reduction of 'because', where the unstressed first syllable is not pronounced at all. The written form, cuz or cos or 'cause, should be avoided. Here's where it's appropriate: - song lyrics, to reflect what is sung and to indicate a single syllable - film or cartoon captions, to show that the speech is very casual - catchphrases, titles, slogans etc, to attract attention and to appear casual It is optional in this context: - very short messages between friends, to save time and characters It is not appropriate in any other written contexts. Learners of English often wrongly believe that spellings which imitate speech ( such as cos/cuz, gonna, wanna and so on) are simply informal language that you can write in any context that isn't formal. Please don't make this mistake.

When speaking well "because" is always preferable. Some people may shorten it in a sentence such as: Why did you say that ? Just cuz I wanted to. It is more like being lazy with language

You can always say 'because'. As Daniel Joseph said, it is very informal, and only used in certain areas. Don't think of using it until you are a fluent speaker.

Hi Dann, in the US also, "'cuz" is used instead of "because" only in informal, casual conversation like a social situation with friends. In more formal situations (and in writing, usually), "because' is used.