There are different ways to express dates in English, and they are different in British English and American English. Let's have a look at some common ways:

We can express dates in numbers, with words, or using a mixture of both.

When writing dates, you can also use the contracted forms of the months. You can learn all of them on the list:

Here are a few examples:

Let's see the days of the month:

There are three common ways to tell the date. Compare these three sentences:

There are different ways of writing dates, depending on the variety of English we are using, the level of politeness, formality or informality of the context, and even personal preference.
We have mentioned some ways of expressing dates, the longer ways are used in more formal writings, they are more polite:

The shorter versions are usually used for letters between friends, informal business letters, memos, etc.

Let's go through some of the differences between American and British English:

The structure of dates in American English is Month/Day/Year. In British English, the structure is Day/Month/Year.
In both styles, the days and years are written numerally and the month is spelled out, here you can see some examples:

Since we usually use the ordinal numbers in speech, we consider them unnecessary in American English formal writings:

In British English, ordinals are used in dates, but not in formal writings:

In American English, we use commas to separate the day from the year.

In British English, commas are mostly considered unnecessary and therefore are omitted in formal writings:

In both American and British English, when only the month and the year are mentioned, it's better not to use commas.

When we fully write dates using numbers, we can use a hyphen (-), a dot (.), or a slash (/) to separate them.

Century is s period of 100 years. For example, the period from the beginning of 1700 until the end of 1799 is called a century. There are two common ways to refer to a century: the first is to simply mention the period, such as the 1700s, while the second is to refer to it as the eighteenth century or 18th century. It is important to note that although these two ways of referring to the century may seem different, they are actually referring to the same period of time.

It is important to note that the number in the name of a century is always one higher than the number of the year that starts the century. For example, we are now in the 21st century, but the years start with the number 20 (2000-2099), same goes for the 18th century which began with the year 1700, so its years start with the number 17 (1700-1799).

There are some recommended ways to write centuries, one is to use all lowercase words, for instance: the seventeenth century. We could also use ordinal numbers, such as the fifth century or 17th century. Centuries are only capitalized if they start a sentence or form part of a title.

We can use a hyphen if an ordinal number and the word 'century' are used as a noun, in this case, they form a compound adjective which needs a hyphen:

Decades are a duration of 10 years. We can write them in different ways. However, it is better to use numerals for decades, using all four digits + 's' and no apostrophe.

Writing the first decade of the century can be confusing since there is no way you can tell 1800s is referring to the century or the decade; therefore, it's better to rewrite the sentence:

Let's have a look at the following table:

BC and AD are initials referring to years in Georgian calendars. BC is used to refer to the years before birth of Jesus Christ, and AD refers to the years after birth of Jesus Christ.

Some people use BCE or CE instead of BC and AD for religious neutrality. This will express the same period, just with religious neutrality.

Since the different styles of expressing dates can be confusing and sometimes can result in very expensive mistakes, ISO is used to prevent problems. 'ISO' is an internationally agreed way to express dates, this is the standard way to show dates on important situations like purchasing airplane tickets, business letters, contracts, and so on.
The structure is YYYY-MM-DD
For instance: 23 September 2019 will be shown as 2019-09-23.

If the date refers to the day of an event, we use the preposition on to refer to the date. Here are a few examples:

The proposition used when referring to the year is in, but remember, in this case, you are not allowed to use the day. For example:

When you are referring to the month as an approximate date, you should use the preposition 'in'. Check out the examples: