I have successfully done a full rewrite.  60kLOC of VBScript&#x2F;ASP to 20kLOC python&#x2F;django.  Added a ton of missing features that wouldn&#x27;t have been possible in the old, clipboard inheritance style.  There was one page on the old site that I had tried to fix up a couple of times and failed completely at.  It was ~2500 lines.  New system it was nothing special, 25 lines in the view and a big but manageable template.<p>I did this whole rewrite in about 9 months including all the work to do the database migration which took a bunch of dry runs and then the actual switchover which took nearly 12 hours to run.<p>What&#x27;s the catch?  I had been working at the company for about 7 years at that point as the sole caretaker of the application so I knew the business needs inside and out, I knew where all the problem areas were and I had plenty of ideas about what features we desperately wanted to add but couldn&#x27;t.  I didn&#x27;t necessarily add all of them up-front but I was able to make good schema decisions to support those later features.<p>Rewrites aren&#x27;t impossible by any means, but I suspect my story is more of the exception than the rule.