The math isn't so easy for Cowboys to add Adrian Peterson's $12.75 million salary

IRVING, Texas -- The math seems so easy. The Dallas Cowboys gained $12.8 million in salary cap space when they restructured Tony Romo's contract. Running back Adrian Peterson is set to make $12.75 million in 2015. One plus one equals the Cowboys are making a trade with the Minnesota Vikings. Not really.

The Cowboys will restructure Romo's contract to help them fit the per-game roster bonuses due Greg Hardy under the cap, the signing of Rolando McClain and the roughly $1.7 million they need for their seven draft picks. As part of Hardy's contract, $8.09 million of his per-game roster bonuses do not count against the cap at the moment because he was on the 53-man roster for just two games last year. He will earn $578,125 for every game he is on the 53-man roster up to $9.5 million.

While it doesn't count against the cap right now, the Cowboys have to keep the room available for when he does earn them. If he is suspended, the Cowboys would receive a cap credit for those bonuses, and that money could help them add players during the season or give them some cash to carry over to 2016 or help in the netting out process if players hit on incentives.

With about $2 million in cap room, the Cowboys need about another $1 million to account for McClain's contract. According to sources, he will make a base salary of $750,000 and will earn up to $3 million based on signing, workout and roster bonuses.

If the Cowboys remain in their current draft positions, they will need the $1.7 million to account for their rookie pool, sort of a cap within the cap that accounts for the team's draft picks and undrafted free agents. When the season starts, teams have to account for the 53 players on the roster. Presently, the top 51 contracts count against the cap. So that's another $1 million that has to be accounted for. Injury settlements and practice squad players also count against the cap.

Add it all up and the Cowboys might need to do more than restructure Romo's contract to make it all fit. And that makes adding Peterson difficult to do but not impossible, but it could require the running back to take less from the Cowboys in order for it to work. Sometimes the math just doesn't work out, especially when it comes to the NFL's salary cap.