It is correct. It means: I am not saying this without reason. I am not saying this for no reason at all. without reason = for nothing Not for anything = has a completely different meaning.

florence, "Not for nothing" is an idiom. It doesn't have to be grammatically correct.Technically it is a double negative and wouldm't t be used in formal writing. As an idiom "Not for nothing" has two different meanings. 1) the double negative "Not for nothing" = for something It's not for nothing that I am saying this. There IS a reason I am saying this. 2) New York slang "Not for nothing" is a translation of the Italian idiom "non per niente". In Italian double negatives are permitted. You could translate it as "I'm not saying this for any personal reason" or " I have nothing to gain by saying this." It is used in the same sense as "just saying". Well, Jimmy, but you look like a gay in that suit, just saying. Well, not for nothing, Jimmy, but you look like a gay in that suit.

Do you mean: "Well, I'll tell you something for nothing, Jimmy, but you look like a gay in that suit." Something for nothing = free advice

It involves the use of two negatives, which is not correct grammar. "Not for anything" is more appropriate to use.