Plastic Economics 101

Captains, considering making offseason roster moves? Trades of/for franchised players are back on the table. Rookie players may be signed to rosters starting January 1st, 2017. If you're having second thoughts about your use of the tag, you're free to drop franchised players and start over from scratch. Any of those moves, obviously, will affect your cap situation. Here's the basic equation to keep in mind when considering any roster moves:
NET = (funds sent + salary acquired) - (funds received + salary dumped)
"NET" being how much the move will increase or decrease your cap space. Sending funds away or bringing in a new player (and their salary) is added cost that cuts into your cap space. Receiving funds adds to your bankroll, while dropping/moving a player (and their salary) frees up additional space under the cap. Thus, a positive "net" reducing your cap space; a negative "net" increasing your cap space. Backwards? No. It's logical to think of it this way since the net value you'll be looking at is what you can spend on your next acquistion.
Most situations are very simple. A player taken in the auction draft is just his salary acquired in the amount you bid. A rookie signing is just $15 in salary acquired. A player dropped is just salary dumped in the amount for which they are currently signed. Trades are more complicated as they inevitably involve moving a player (and their salary), in addition to the likelihood of draft funds also being involved. The variable that we most often see overlooked in a trade scenario is the player salary that's involved - resulting in teams initially offering or asking for more than can possibly be dealt. So, in an attempt to preempt any of that this year, here's an example team roster and their cap to walk through the scenarios.
CAPTAIN FRANCHISE MAX NEXT
MOVE (NET)
SLOT 4 SLOT 5 SLOT 6
$35 $40 $115 $10
RESERVED
$10
RESERVED
 
Pretty straightforward: a team with a $210 cap. $75 spent on the captain and franchised player. No traded in funds. No cap hit. At least $10 must be reserved for each remaining roster slot up to the minimum of 5 players. So, abiding the rules of the salary cap and draft, the team is allowed to use up to $115 (net) on their next move.
Auction Draft: If they wait until the Draft, they could use all of that $115 on their first pick. This would put them at 3 players, with $20 for the final two necessary roster spots. If they use this max bid, the most they could spend on their next pick (fourth roster spot) would be $10.
Rookie Signing: If they sign a rookie before the draft, then that fills the third roster spot at a cost of $15 against the cap. So, they'd be at $90 in 3 players. Since they'd only be required to fill 2 more roster spots, only $10 dollars would have to be reserved for the fifth player. This would make the team's maximum net next move $110 ($210 - $90 - $10).
Release Player: If the captain decides to start fresh and cuts his $40 franchise player before the draft, then that $40 would be added back to his space under the cap. He'd also add one more roster spot that needs to be filled, thus requiring an additional $10 to be reserved. In this case the team's max net next move would be $145 ($210 - $35 - $30).
Trade: If they are looking to trade for a $45 player, then they could trade up to $70 only ($115 maximum net next move less the $45 salary of the incoming player). If it's a $30 player they want to bring in, then they could trade up to $85 ($115 less the $30 salary of the player acquired). As with the "max bid" scenario at auction, the team would be left with only $20 for it's final two roster spots if they traded this amount, and could only spend at most $10 on their next signing.
Review the 2017 Team Cap Situations Below. Table updated 1/31.
CAP
SPACE
$125 $66 $265 $125 $170 $120 $155 $209
RESERVED
FUNDS
$20 $0 $30 $10 $20 $20 $20 $30
MAX NEXT 
MOVE (NET)
$105 $66 $235 $115 $150 $100 $135 $179