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:
6/10/17
(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:
10/6/17
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.
Common Mistakes in Business English 
How to say e.g. 1800 in British and American. I’m slightly confused by the American use of “… hundreds” instead of “… century”. And am I correct: “the turn of the 20th century” is e.g. 1898-1902?
Joela – 1800 is said as “eighteen hundred”. If someone talks about “the eighteen hundreds” (the 1800s) they would usually be referring to the entire 19th century, i.e. from 1800 to 1899. However, they could also be referring to the first decade of the 19th century, i.e. the years 1800-1810.
We are now in the 21st century (the 2000s or “two thousands”); however the 2000s can also mean the decade 2000-2010, as opposed to the 2010s, which is the current decade (the “twenty tens”).
The phrase “the turn of the 20th century” can be confusing. Back in the 20th century we used the phrase “the turn of the century” to refer to the late 1890s to the early 1900s. Now, I guess the same phrase would refer to the late 1990s to the early 2000s.
In British English “the turn of the 20th century” refers to the 1890s-1900s period, although not everyone will necessarily know this. So the 1990s-2000s period is “the turn of the 21st century”.
In American English there is apparently no general agreement. The Chicago Manual of Style states that “the turn of the 19th century” could be understood to mean “the turn of the 19th century into the 20th century”, i.e. the 1890s-1900s period.
Yeah, I totally agree!
Good post. I learn something new and challenging on websites I stumbleupon everyday.
It’s always helpful to read through articles from other writers and use something from their websites.
Thank you, very valuable information, Barnaby. Note that Canadian English discourages us using the ordinal numbers format: March 15th, 1993 (source: https://www.btb.termiumplus.gc.ca/tcdnstyl-chap?lang=eng&lettr=chapsect5&info0=5.14). It is, however, allowed when the day and month only are given: March 15th.
Also, it is curious that even though you are mentioning above that 6 October 2017 is rather a British format and October 6, 2017 is rather a US format, both are used, I would say, very frequently here in Canada..
To avoid the confusion between month and date order when using numbers, we are encouraged to write the month in letters.
That’s it for now, thank you for sharing the rules and your thoughts too!
Thanks for your comments Marina. Anything else you can add on Canadian English would be much appreciated!
Is it fine to say “two thousand something” as well as saying “twenty something” for all of the 2010s years 2010-2019? For example: Is it ok to express the current year by saying “two thousand eighteen” as well as saying “twenty eighteen”? Because I have heard 2018 as well as all the other 2010s years said in both ways.
I think it’s fine to use both ways, but it seems to be becoming increasingly popular to use “twenty something”. I guess we were saying “two thousand (and) something” because 2000 had long been “the year two thousand”, and we have Arthur C Clarke and Stanley Kubrick to thank for “two thousand and one”. (And “twenty oh one” sounds awfully cumbersome.)
But when we get to 2020 I can’t imagine anyone will call it “two thousand twenty” because “twenty twenty” slips so easily off the tongue. As will “twenty twenty one” etc etc.
Ok thanks. Are you British or American if I don’t mind asking?
British living in Poland.
Hi. You mention that when writing day-month-year writing the day as an ordinal number (1st, 2nd, 3rd) used to be more popular. Is that true? I remember writing days that way also and I’m curious when it changed. I know that you’re British. I used to live in the U.S. I found this blog post when I was researching about whether days were ever written as ordinal numbers. You are probably the only person who is saying anything about it 🙂
I don’t think it changed at any precise time – it’s a gradual thing, and some people still use ordinal numbers. Maybe it’s related to using computers and the general trend of reducing unnecessary typing.