I have no idea whether this estimate is still valid, but back in the days when I was working with O’Connor & Associates, the head of technology (and O’Connor had a well run technology operation) said the cost of documenting software (as in having the developers write up what they did in sufficient detail so a third party could maintain the it) was an additional 20%. It was very difficult to get traders to pay for it, ironically not so much for the hard dollar costs, but the fact that IT was resource constrained. The idea that the coders would spend a lot of time on leaving a paper trail, rather than getting to a business center’s urgent need, was a hard sell.

But Lehman illustrates what happens when you do what most places do, and skip documentation. Now of course, modern IT on the Street was supposed to be using more off the shelf software and doing less custom development, but you would never know that reading this Financial Times story: