legacy software Tag

Two computers from the 1980s are standing on an office desk.   We see it all the time: a company has a long-established software system that's either fully custom or has been customized to fit just right. It's perfect, or as nearly perfect as software can be. And then the company grows. It evolves with the changing marketplace. Little by little, that perfect fit starts to pinch here and sag there. You know you'll need to do something about that legacy software eventually, but not now. When does "eventually" become "now"? How can you tell when it's time to overhaul your legacy system?