2015-07-25 - The Correct Date Format

Occasionally you will hear the British and the Americans fighting over what is the correct date format. The Americans think it’s MM/DD/YYYY and the British think it’s DD/MM/YYYY, but they are both wrong because the correct format is YYYY-MM-DD.

One reason is ambiguity. Without some additional context it’s hard to tell if 12/01/2012 is December 1st, 2012 or the 12th of January, 2012. This ambiguity doesn’t exist for YYYY-MM-DD because there’s no YYYY-DD-MM in common usage. This means that 2012-12-01 is always December 1st, 2012 and there’s no chance of reading the date wrong.

The second reason is sorting. When dates are sorted as text they are ordered by the first part of the date first. This means that MM/DD/YYYY sorts by month, DD/MM/YYYY sorts by day, and YYYY-MM-DD sorts by year. Ideally you want dates sorted chronologically which means it’s better to have the largest part first. YYYY-MM-DD does this while the other formats will mix dates up.

Consider the dates April 2nd 2012, April 3rd 2012, June 15th 2012, April 17th 2013, and June 2nd 2013. The following table shows these dates sorted according to the various date formats.

With YYYY-MM-DD format everything is in order. All the 2012 dates come before the 2013 dates, All the April dates come before the June dates within the same year. With MM/DD/YYYY we have 2012 dates before and after the 2013 dates. With DD/MM/YYYY we have 2013 dates before 2012 dates and June dates before April dates.

Also I personally think the dashes look better.