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 which country it comes from by looking at the notation — but sometimes not.

Some Europeans already start to despair with the A.M. and P.M. times, as well as the different spellings between British English and American English that 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 31.12.2023 format is easy to understand: It is the 31st day of the 12th month in the year 2023. Points are used as separators, which makes this date format visually easy to recognize. But dots are not used as separators everywhere. Depending on the country, they are sometimes slashes or hyphens. Then the 31.12.2023 becomes the 31/12/2023 or 12/31/2023. The order in which the day, month and year are given depends on the country.

US American format: 12/31/2023

The US-Americans already have a deviation in the spoken word order, it is "December 31st." Accordingly, the day is written after the month. Central and South Americans use a different notation, in which hyphens are also used, but day and month are in reverse order: Instead of 12/31 it is 31/12. In the rest of the world, it becomes a guessing game. For example, in the Philippines, which was occupied by the Americans for around 40 years, the US format is just as common.

British-English format: 31/12/2023

This arrangement of the individual numbers corresponds to the European 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 uncertain because this is not followed consistently. In addition, some countries also use a hyphen instead of a slash.

Finally, standardization with ISO 8601: 2023-12-31

Writing date and time formats Due to increasing digitization, a rarely-used format has become more and more popular over the last few decades: 2023-12-31, meaning year first, then the month and finally the day. In this descending order, even the hyphens could be removed (if you always write month and day with two digits) and you would still be able to recognize the date clearly. Even more, the date can be sorted alphabetically as well as numerically. This standard was tried in 1988 but only made it into the international ISO 8601 a few years ago. It has hasn’t really become established in everyday life yet.


If a date is not separated by dots ("31.12.2023") or written in the rather recent format "2023-12-31," there is likely to be confusion. The new standard according to ISO 8601 with a written out four-digit year is recommended because otherwise, the year could be confused with the day in the British variant. Apart from that, the only thing left to do is to mark the individual date components: "Dec 31, 2023" or "31st Dec 2023" aren’t much longer, but they are understandable.

Times with AM, PM, MN and NN

Fortunately, the times are not as confusing as the 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 "17:30" or "5:30 pm." The 12-hour system is mainly used in English-speaking countries, the USA, Australia and the English-speaking parts of Canada. 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 A.M." is half past 12:30 at night, and "12:30 P.M." is half an hour past noon. This is easier is read for the hours from 1-9 because leading zeros are left out to distinguish from the 24-hour clock. The time "17:30" then becomes the easily distinguishable "5:30 P.M."

MN and NN: Midnight and noon

The notation 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 P.M.," although this "pm" does not begin until a second later. In order to prevent this, the additional notation "nn" (noon) is only used for the exact 12 o'clock time.

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

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 12-hour system. 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 "12 P.M." cannot exist at night.
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