If i killed someone1 who tried to rob me(for example) with knife, would i still go to jail?

On my road to home some madman or just a mugger with knife trying to rob me or injure,kill..idk..threatening to do something gay..Lets say in fight i box him once and he dies...(not that he falls down and i keep kick him until he is dead..) Would i still go to jail? isnt it self-defence?