Cambridge Grammar says

We use an apostrophe -s construction (in a year’s time, in two months’ time) to say when something will happen.

Sometimes, I see people use "5 days' leave" or "On New Year’s Day"

Why not "5 day leave" or "On New Year Day" or "in a year time"?


The question addresses Inanimate Possessives.

  • As a rule, nouns referring to inanimate things should not be in the possessive. Use an “of” phrase instead.

  • the bottom of the barrel (NOT: the barrel’s bottom)

  • the wording of the agreement (NOT: the agreement’s wording
  • the lower level of the terminal (NOT: the terminal’s lower level)

However, in reference to time and measurement, and in phrases implying personification, possessive form has become accepted usage:

  • a day’s notice
  • an hour’s work
  • two years’ progress (plural possessive)
  • two weeks’ salary (plural possessive)


Time periods are sometimes put into possessive form, to express the duration of or time associated with the modified noun:

  • the Hundred Years' War
  • a day's pay
  • two weeks' notice

The paraphrase with of is often un-idiomatic or ambiguous in these cases.


  • So, the pay belongs to the day? The notice belongs to the two weeks? The work belongs to the hour? Somehow, none of this is convincing. There are far more apostrophes that are wrong than are correctly used, and I believe here are some! – Tim Jun 19 '17 at 13:15
  • What's wrong with the first 3? `the barrel's bottom", "the agreement's wording", "the terminal's lower level" all sound right (the first is a little iffy, but still sounds ok) – Adrian Nov 29 '17 at 19:41

's means "of".

So "five days' leave" means "a leave of five days". "New Year's Day" means "the day of the new year". With such named days, usage has varied so the apostrophe is rarely used.

An alternate for the former case is to omit the "of" and make the duration an adjective by adding a hyphen: A five-day leave.

  • 1
    When I was at school (well over half a century ago) I was told that the apostrophe was to replace the missing letters in such as "John his book" - "John's book"; "New Year its Day" - "New Year's Day". But I have seen an alternative explanation on this site, but sadly have forgotten what it is. – WS2 Apr 15 '17 at 6:35
  • Further to the above, according to @Cerberus it is a shortened form of the old genitive case ending -es. See - english.stackexchange.com/questions/9467/… – WS2 Apr 15 '17 at 6:41
  • 's does indeed often mean 'of', or with reference to something belonging to. As i the dog's tail. The taILbelongs to the dog. However5, in your answer, you infer that the leave belongs to the days, and the day belongs to New Year. Doesn't sound too feasible. – Tim Jun 19 '17 at 13:12

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