I hadn't heard of that particular trick, but it's a cute one.
For calendar dates, I'm using the COleDateTime class that MFC provides (and which -- I suspect -- is optimized to use some of these tricks).
When I'm dealing with non-calendar dates (which occur in those pesky 360-day and 364-day years), I do my own calculation, but those are much more regular than the real calendar. The problem is in mapping the calendar dates onto the non-calendar time periods, but I think what I'm going to do is work with elapsed days from the start of the year; then ram the extra days into the last month of the fiscal year. I won't calculate interest on those days, but if a payment is due in that range, I'll do it on the last day of the fiscal year.
Re: While I looked around at my possibilities
For calendar dates, I'm using the COleDateTime class that MFC provides (and which -- I suspect -- is optimized to use some of these tricks).
When I'm dealing with non-calendar dates (which occur in those pesky 360-day and 364-day years), I do my own calculation, but those are much more regular than the real calendar. The problem is in mapping the calendar dates onto the non-calendar time periods, but I think what I'm going to do is work with elapsed days from the start of the year; then ram the extra days into the last month of the fiscal year. I won't calculate interest on those days, but if a payment is due in that range, I'll do it on the last day of the fiscal year.