Unlike most other cruise lines and land-based casinos, Carnival does not have a published schedule of comps.
The only comp that Carnival advertises is you must accumulate I think 1500 points to get free drinks while playing. But you may already have that immediately depending upon the rate code you booked.
Any comps above that - free steakhouse meals, free balcony cabins, etc., are at the discretion of the casino hosts. There is no formula. Anything that people may respond with is just speculation.