Date and time notation in the United States

Date and time notation in the United States differs from that used in other English-speaking countries; in particular, the date notation is not used by any other country in the world. Traditionally, dates are written in the "month day, year" order ("December 02, 1999"), and time in 12-hour notation ("11:00 p.m."). The internationally more common notations are used in some professional environments, such as in the military.

In the United States, dates are traditionally written in the "month, day, year" order, with neither increasing nor decreasing order of significance. This order is used in both the traditional all-numeric date (e.g., "1/21/16" or "01/21/2016") as well as in the expanded form (e.g., "January 21, 2016") (usually spoken with the year as a cardinal number and the day as an ordinal number; e.g., "January twenty-first, two thousand sixteen"), with the historical rationale that the year was often of lesser importance. The most commonly used separator in the all-numeric form is the slash (/), although the hyphen (-) and period (.) have also emerged in the all-numeric format recently due to globalization.

The day-month-year order has been increasing in usage since the early 1980s. The month is usually written as an abbreviated name, as in "19-Jul-1922". Many genealogical databases and the Modern Language Association citation style use this format. When filling in the Form I-94 cards and new customs declaration cards used for people entering the U.S., passengers are requested to write pertinent dates in the numeric "dd mm yy" format (e.g. "19 07 22"). Visas and passports issued by the U.S. State Department also use this format. In the food industry, many companies in the US are starting to print expiration dates in the "dd mmm yyyy" order (e.g. "25 DEC 2006").

The fully written "day-month-year" (e.g., 25 May 2006) in written American English is becoming more common outside of the media industry and legal documents, particularly in university publications and in some international-influenced publications as a means of dealing with ambiguity. However, most Americans (in most informal documents) would still write "May 25, 2006". Speaking the "day month year" format is still somewhat rare, with the exception of holidays such as the Fourth of July.

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