Good question and would make for a good article to exploit the ISO_Week datepart (came out with 2008) of the datetime functions. The question is, what do you want done with years that have 53 fiscal weeks in them? One company I worked at used 6-4-4, 5-4-4, 5-4-4, 5-4-4 and another used 5-4-4, 5-4-4, 5-4-4, 5-4-5.

Of course, I've also seen some non-US companies that started their work-week on Thursdays instead of Mondays and a lot of US companies that start their work week on Sundays instead of Mondays (working for one right now), which always makes things a bit more interesting in calculating 5-4-4 quarters.

To be honest, I think calculating things by quarter is a bit archaic now. It was done to make reporting by accountants a whole lot easier in the long gone days before computers.