Writing date and time formats

Writing date and time formats

Worldwide there are different spellings for a date and also for times. This regularly causes confusion. Sometimes you can tell from the spelling which country it comes from - but sometimes not.

Some Europeans start to despair already with the AM and PM times. But at the latest with the different spellings British English and American English get mixed up.

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Ways of writing the date

In many European countries the date has a clear structure, which is also quite easy to recognize. The 31.12.2021 is easy to understand: It is the 31st day of the 12th month in the year 2021. Points are used as separators, which makes this date format also visually easy to recognize. But not everywhere dots are used as separators. Depending on the country, they are sometimes slashes or hyphens. Then the 31.12.2021 becomes the 31/12/2021 or also the 12/31/2021. The order in which the day, month and year are given depends on the country concerned.

US American format: 12/31/2021

The US-Americans already have a deviation in the spoken word order, it is the "december 31st". Accordingly, the day is written after the month. Already Canadians and most Central and South Americans use a different spelling, in which hyphens are also used, but day and months are in reverse order. In the rest of the world it becomes a guessing game. For example, in the Philippines, which was occupied by the US Americans for around 40 years, the US format is just as common.

British-English format: 31/12/2021

This arrangement of the individual numbers corresponds to the German format, so the day is written first and then the month. Due to the slashes that are also used here, it is not clear whether the format is US English or British English. Therefore, sometimes dots are used or the name of the month is written out. But there is still an uncertainty, because this is not consistently followed. In addition, some countries also use a hyphen instead of a slash.

Finally a standardization by ISO 8601: 2021-12-31

Due to increasing digitization, a format that has been used rather rarely so far has become more and more popular in the last few decades: 2021-12-31, meaning first the year, then the month and finally the day. By this descending order even the hyphens could be removed (if you always write month and day with 2 digits) and still you would be able to recognize the date clearly. Even more so, the date can be sorted alphabetically as well as numerically. Already in 1988 this standard was tried to establish, only a few years ago it finally made it into the international ISO 8601. It has hardly become established in everyday life yet.


If a date is not separated by dots ("31.12.2021") or written in the rather recent form "2021-12-31", confusion is likely to occur. The new standard according to ISO 8601 with a written out 4-digit year is of course recommended, because otherwise the year could again be confused with the day of the British variant. Apart from that, the only thing left to do is to mark the individual date components: "Dec 31, 2021" or "31st Dec 2021" are hardly longer, but they are understandable.

Times with AM, PM, MN and NN

Fortunately, the times are not as confusing as the often different ways of writing the date. As an internationally understandable format, it is becoming more and more common to use the 24-hour format "05:30". It is important here to write the hour with two digits, i.e. with a leading zero. This turns the time into the early morning at half past five. Accordingly, half past five in the evening would be "5:30".

The 12-hour system is mainly used in the English-speaking countries. The USA, Canada and Australia. Great Britain itself is excluded from this and uses the 24-hour format that is common in Europe.

AM and PM: Morning and afternoon.

For a European, "12:30" is clearly lunchtime, while 00:30 means a time shortly after midnight. In the English-speaking world, the 12-hour format is much more widespread and there is no such thing as a zero hour. Both times are written as "12:30". To make it clear that you mean the hour after midnight or the hour after noon, you use the Latin abbreviations AM and PM,

AM = Ante meridiem = morning from 00:01 to 11:59
PM = Post meridiem = afternoon from 12:01 to 23:59

So "12:30 am" is half past 12:30 at night, and "12:30 pm" is half an hour past noon. At all hours from 1-9, the recognition is even a bit easier, because in order to stand out from the 24-hour format also optically, leading zeros are left out. The time "17:30" then becomes an easily distinguishable "5:30 pm".

MN and NN: Midnight and noon

The spelling is somewhat inconsistent when it comes to the exact time at noon or midnight. Because "pm" actually stands for the Latin "post meridiem", i.e. AFTER noon, which would mean 12 o'clock at night. In practice, 12 o'clock at noon is often erroneously called "12 pm", although this "pm" does not begin until a second later. In order to prevent this, the additional indication "nn" (noon) is only used for the exact 12 o'clock time.

There is another abbreviation "mn" (midnight), but it is rarely and often wrongly used. If you would use "12 midnight" as time specification, it would not be clear which date you mean. Because in the 12-hour format there is no zeroth hour and 00:10 is expressed as "12:10 am". So a "12 midnight" could be midnight at the beginning as well as at the end of a day. Correctly, the time at midnight is "12 am".

Some examples

24-hour format12-hour format
00:0012:00 am or 12:00 mn
00:3012:30 am
05:305:30 am
12:0012:00 nn
12:3012:30 pm
17:305:30 pm
23:5911:59 pm

24 o'clock does not exist

A day has 24 hours and starts with the first second at 00:00:00. So the 24 hours are finished with the completion of the last second, which starts at 23:59:59. The time 24:00:00 does not exist in the 24-hour system nor in the one with 12 hours. The next second is the first second of the next day and therefore 00:00:00. With such an explanation it is easy to remember why a "12 pm" cannot exist at night.
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