Each week proofreader Hannah Jones discusses and offers a remedy to common problems we encounter when writing. Today she demonstrates the use of apostrophes with time periods.
A common stumbling block for many writers is whether to use an apostrophe in phrases such as five years time/five year's time. Which is the correct usage?
An apostrophe should be used in phrases where a time period modifies a noun (e.g. notice):
two weeks' notice
a month's holiday
five years' time
Note that, just as in possessive constructions, the apostrophe comes before the s for singular nouns and after the s for plural nouns:
a day's work (singular)
20 years' experience (plural)
However, an apostrophe is not used when a time period is modifying an adjective (e.g. old):
80 years old
five days long
six months pregnant