I'm going to say 25%, so the company replaces 10k SDE's every four years at a cost of $4.5 billion dollars (based on 4x salary replacement cost and 10k SDEs).

I'm going to say 25%, so the company replaces 10k SDE's every four years at a cost of $4.5 billion dollars (based on 4x salary replacement cost and 10k SDEs). Why 4x? There's an army of HR and recruiting people. There's tens of thousands of interviews. And people don't really start paying off until their third or fourth year in a new job.