甲斐(かい)があるTo be (not) worth, To (not) pay off

甲斐(かい), a noun meaning 'worth' or 'effect', will often be used following verbs or nouns, in order to show that (A) was or will be worth doing. In many cases, this grammar point will be seen in hiragana, and will appear as either かい or がい, depending on how it is conjugating with the previous word. Possible translations include things like 'it is worth doing (A)', or '(A) will pay off'.

が and the う-Verb ある 'to be' will follow かい. This states that the 'worth of (A) exists'. Occasionally, the が will be omitted. When following verbs, がい will be used after the ます-stem, or かい may be used after any standard form.

The primary difference between these conjugation patterns is that there is more focus on the tense of the verb with かい, whereas がい will frequently have the nuance of it 'always being worth (A)'.

When pairing with nouns, の will be required before かいがある.

Alternatively, かいがない may be used in order to indicate that it is 'not' worth doing something.

かいがある is primarily used when the speaker wants to convey that a positive result will come from something that is either difficult or unpleasant.