The NFL has reportedly told general managers and other team executives that the salary cap for the 2016 season is expected to be between $147 million and $155 million, according to Bleacher Report's Jason Cole. That would be an increase of between $3.72M and $11.72M from this year's cap, which was set at $143.28M.
According to OverTheCap.com, the Colts are estimated to have $128,333,585 against the salary cap next year, when factoring in those players under contract for 2016 and the dead money. And, keep in mind, this is before any offseason moves made to clear up salary cap space that might come through cutting players (there are some obvious candidates). As it currently stands with the latest reported cap number, though, it's expected that the Colts could have somewhere between $18.67 million and $26.67 million in salary cap space available for next season.
Per OTC, the top five for the Colts in terms of cap hit in 2016 are as follows: quarterback Andrew Luck ($16.155M), wide receiver T.Y. Hilton ($11.0M), left tackle Anthony Castonzo ($9.8M), cornerback Vontae Davis ($8.25M), and wide receiver Andre Johnson ($7.5M). I don't think there will be any complaints with the top four, as I think it's rather unanimous that those are the Colts' four best players (on either offense or defense), regardless of what order you prefer. But Andre Johnson at number five is obviously out of place, and he could be a prime candidate to be gone after the year (the Colts could save $5M toward the cap next year by cutting him).
The Colts will also have some decisions to make about who to re-sign. According to Spotrac, here are a few of the most notable players who will be free agents after the year and who the Colts will have to make a decision on: quarterback Matt Hasselbeck, kicker Adam Vinatieri, tight ends Coby Fleener and Dwayne Allen, cornerback Greg Toler, inside linebacker Jerrell Freeman, and safety Dwight Lowery, among others.
In other words, it sounds like the Colts will have some salary cap room to work with, but we shouldn't expect another spending spree in free agency. Rather, with the Colts at the stage of having to re-sign talent rather than add talent in free agency, we'll likely see them invest a significant portion into keeping players around and the draft rather than going after veteran free agents. That's not saying that they will be completely silent, but I wouldn't expect that to be the main focus this offseason unlike in past years.