Formal:
* Kei te kata ahau. (This is the most literal and formal translation.)
Informal:
* Kata ana ahau. (This is more casual and conversational.)
* E kata ana ahau. (This is similar to the previous one, but slightly more emphatic.)
Other options:
* Kata ahau. (This is a very short and informal way to say "I am laughing.")
* He kata tenei! (This translates literally as "This is laughter!" and expresses a strong sense of amusement.)
The best choice for you will depend on the situation and the tone you want to convey.