Did you know the Month/Day/Year (12/01/1994) format is almost exclusive to the U.S.? Belize and Micronesia also use this format and it is secondary in Canada and the Philippines. Anywhere else you live or travel, you're more likely to find the date written in the little endian format: Day/Month/Year (01/12/1994).
Here are some of the regions that format their date in the Day/Month/Year format:
Things get interesting when you're in Spanish-speaking countries. Look to see if most of the people living or working around you drop the zero when the day or month is a single digit. That seems to be the norm. So, March 2, 2017 would be 2/3/2017 instead of 02/03/2017.
So many systems for one simple concept, right? In an effort to avoid international miscommunication, the International Standard ISO 8601 was created. If an American writes May 3, 1988 as 05/03/1988 but an Italian writes May 3, 1988 as 03/05/1988 who's to know what's what!
As such, the ISO 8601 is:
There are other forms of writing the date used around the world, too. The most common of these is the big endian form, which seeks to avoid confusion by placing the year first, similar to the International Standard. Much of Asia uses this form when writing the date.
Here's an example:
Interestingly, in Hungary, a comma isn't used when writing the date either. Instead, there's a dot after the year. Also, the first letter of the month isn't capitalized.
Here's an example:
When writing the date with numbers only, they may be separated by a hyphen (-), slash (/), or dot (.) Most formal writings will accept a slash (/). Notice, however, that the ISO standard uses hyphens (-).
It's fair to say these methods are interchangeable. When writing an academic paper, you'll want to consult your professor's preferred method of citation. When filling out official documents or forms, note the instructions and sample text carefully.
While we're on the subject of formality, you never want to abbreviate the month (i.e. Nov. for November) in a formal document or communication. As a rule of thumb, abbreviated versions of words are far less formal.
In formal U.S. writings, you never want to omit the year or use a purely numerical form for the date. For example, if you were to write a formal business letter, you'd write out the entire date, including the full month (January 1, 2011). Writing it out in such a way allows the notation to be understood by everyone.
In formal European writings, the date is typically written in a similar fashion to the American version. So July 4, 2011 would simply have the month and day switched around, making it 4 July 2011. Notice in a formal European version of the date, there's no comma. The comma separating the date from the year is an Americanism that the Europeans do not follow.
In the end, most folks won't be too confused if you use a different format than what they're used to. The point is to try to make the other party's formatting your primary objective and also to be consistent. When in doubt, spell out the month to avoid that 05/03/1988 vs. 03/05/1988 debacle. When writing a research paper, consult your citation manual. And if you're writing in a formal setting, even if it's an email, avoid all abbreviations. This will help keep you on the safe side of formal date writing.