Just so I understand...

You are developing a financial application and want something to work for now, hoping it will work in the future? I have developed financial applications and find that proven patterns solve way more problems than you can even anticipate. If this is a long-term application that will do many reports or screens based on the same periods, the recommendation for the calendar table is really your best bet. It pretty much guarantess consistant results everywhere you may need that informaiton.

Just my two cents worth.