There are plenty of situations where it makes sense to put a date in a filename but if you don’t use the right date format the files may sort in unhelpful ways. For instance, using the names of months is a bad idea since they’ll sort alphabetically putting April before January. Although the Mac’s Finder is smart enough to sort filename-3 before filename-20, most other operating systems are not (because 2 comes before 3). To make your life (and the lives of everyone with whom you share files) a little easier, use this date format which is guaranteed to sort correctly everywhere: YYYY-MM-DD. That translates to a four-digit year, followed by a two-digit month (with a leading zero if necessary), and a two-digit day (again, with a leading zero if need be).