According to puckpedia maximum retention is 50%. Sens have 25%, Bruins retain 25% which equals 50% which is what I said originally.Correct
Double retention can get you to 25%. Happened a bunch.
Retained Salary | Puckpedia
When teams trade a player, they can retain, or keep, some of the players' salary and cap hit. The team keeps a % of both the cap hit and salary for the remainder of the contract. Therefore, if a Player with a Salary of $2.0M and a Cap Hit/AAV of $3.0M is traded with 20% retention, the trading...
puckpedia.com