Calendar-based stuff is absurdly difficult to get right. Even if you have something that seems to work you likely have a hidden error somewhere. That's not r

Calendar-based stuff is absurdly difficult to get right. Even if you have something that seems to work you likely have a hidden error somewhere. That's not really an excuse -- edge conditions like DST on/off, and end-of-year should be first on your test list. But calendars suck to work with.