For example: Team X is at $64M (i.e. over the cap), Team Y is at $67M. Team X sends team Y $10M in salary, the most Team Y can send Team X is $12.6M and the least team Y can send team X is $7.9M.
This is why I support losing Calderon's contract. With a weak draft this year and sketchy free agency class, the best way to improve the roster will most likely be on the trade front. Cap space is not all about free agency, it helps to take back more money in trades without worrying about being limited to 125% + 100K. This is why many trades in the NBA do not materialize because the numbers do not work - even being off $30K on a deal with $20M in salaries ruins the trade.