There is a difference between how dates are written in British and American English.
In British English dates are usually written in the day-month-year format, for example:
6 October 2017
In American English dates are usually written in the month-day-year format:
October 6, 2017
(note the comma between the day and the year)
In British English we can also use the abbreviated form as follows:
(different punctuation marks may be used: 6.10.17 or 6-10-17)
Caution is required here, however, as Americans usually put the month first:
As you can imagine, this can lead to ambiguity as the above date might be understood as 10 June 2017 instead of 6 October 2017.
In an attempt to avoid ambiguity resulting from the different ways of writing dates around the world, an ISO standard was adopted in 1988. This uses the year-month-day format as follows: 2017-10-6. However, this format is not widely used in Britain or the US.
How to say dates
6 October 2017 is said as follows:
the sixth of October twenty-seventeen (note “the” and “of”)
October 6, 2017 is said as follows:
October sixth, twenty-seventeen
23 April 2005 is said as follows:
the twenty-third of April two thousand and five
The year 2000 is said as “two thousand”.
We tend to say “two thousand and…” up to 2009.
2010 may be said as “two thousand and ten” or “twenty-ten”.
From 2011 onwards we tend to say “twenty-eleven”, “twenty-twelve” etc.
Years before 2000 are said as in these examples:
1984 — nineteen eighty-four
1902 — nineteen oh two
1848 — eighteen forty-eight
1492 — fourteen ninety-two
1066 — ten sixty-six
As we use ordinal numbers (first, second, third, fourth, etc.) when we say dates, sometimes we add the endings of ordinal numbers when we write dates, as follows:
6th October 2017
October 6th, 2017
This style used to be more popular, but it seems to be rather out of fashion now. If you do use it, remember to add the correct ending (st, nd, rd or th):
1st, 2nd, 3rd, 4th, 5th, 6th, then use th until 21st, 22nd, 23rd, 24th, etc.
Abbreviations of months
All the names of the months have short forms except May and June:
Jan, Feb, Mar, Apr, Jul, Aug, Sept, Oct, Nov, Dec
Remember we always capitalise months, whether we write them in full or abbreviate them. Some style guides may add a full stop/period after the abbreviation, but it is generally OK not to use one.
Abbreviations of days
All the names of days have short forms:
Mon, Tues/Tue, Wed, Thurs/Thu, Fri, Sat, Sun
For Tuesday and Thursday, Tues and Thurs are common, but for the sake of consistency I advocate the three-letter style – bolded above.
Remember we always capitalise days, whether we write them in full or abbreviate them. Some style guides may add a full stop/period after the abbreviation, but it is generally OK not to use one.