Blackjack question

I have a friend that likes to double down on 12 against a 2 through 6. Could anyone please tell the percentage edge against him on this play?


I'd really appreciate a straight answer. Thanks.

Yeah...6 deck Dealer Stands on 17.


2... -.504


3... -.463


4... -.421


5...-.377


6...-.338


That means for example every time your friend doubles down his 12 on dealers 5...he will or can expect to lose 38% of his wager.