Years

Dates are ubiquitous in a wide range of written texts. For something so straightforward, they can also generate a lot of uncertainty when it comes to citing date ranges, decades and eras. The following guide represents Australian practice.

Single years
Use all 4 digits in body text
2020
1901
In body text, it is clearest to show all 4 digits of a year.
In 2000, our region was declared polio free.
In 00, our region was declared polio free.
If you must abbreviate the year, use an apostrophe to show the missing digits. Make sure it’s an apostrophe and not a right-facing quote mark, which your word processor might insert automatically.

Few now remember the Y2K threat of ’99.

Few now remember the Y2K threat of ‘99.

Of course, you can always abbreviate years in dates that use the DD-MM-YY format where space is limited, such as in tables or file labels.

Spans
To show a span of years, use an en dash (without spaces) or the word ‘to’ 
1931–35
1858 to 1860

If your span uses an en dash, you can shorten the second year to 2 digits, but only if the meaning is clear.

2011–13
1999–01
Financial years
Use an en dash and abbreviate the second year to 2 digits
2017–18
2003–04

In a financial context, also use an en dash (–) for financial years, and not a hyphen (-) or a forward slash (/).

The 2019–20 annual report
The 2019/20 annual report
Decades
Use numerals but no apostrophe
2010s
1990s

Perhaps the most common mistake when formatting dates is to add an apostrophe when pluralising a decade. This is because adding the letter ‘s’ to a numeral looks like either a contraction or a possessive, where an apostrophe would normally be used. But this is not the case, so you should simply add an ‘s’ to form a plural.

The ‘Noughties’ is another name for the 2000s.
The Privacy Act was introduced in the 1980’s.
Centuries
Use numerals with a lower case ‘c’
the 5th century
19th century laws

For centuries, follow the regular rules for ordinal numbers and format using numerals rather than words. Don’t use superscript for the suffixes on ordinal numbers.

the 21st century
the 21st century

Where an ordinal number is part of a compound adjective, the ASG recommends leaving out a hyphen because there’s little risk that a word–number compound will be misread.

This is an 18th century building.
Calendar eras
Use ‘BCE’ and ‘CE’, not ‘BC’ and ‘AD’
2020 CE
300 BCE

If your text is historical, you might need to add calendar eras to distinguish dates.

Prefer ‘BCE’ (Before the Common Era) and ‘CE’ (Common Era). These are equivalent to ‘BC’ (Before Christ) and ‘AD’ (Anno Domini).

The common era references are replacing BC and AD in common usage because they are more neutral and not tied to religion.

See also:   Dashes - – —,  Forward slashes /,  Ordinal numbers