As others have indicated, this method has some practical problems.

Instead of being more-or-less constant like a paycheck, your withdrawal amounts will bounce all around. Your Jan 2009 draw would have been about half of your Jan 2008 draw. And Jan 2010 would be about 1 1/2 times your Jan 2009 draw.

It's pretty hard to handle a budget when your income jumps around that much.