When to use them, when to leave them out
First, look it up in the dictionary and go with what they say. If you’re still not sure, read this.
There are two situations where you’ll likely to need a hyphen.
When an adjective is made up of more than one word
We call these compound adjectives. This is how they work:
An adjective describes a noun, like ‘the written word’.
A compound adjective does the same thing, but it’s made up of more than one word, like ‘round-the-clock support’.
A compound adjective usually gets a hyphen when it comes before a noun, like in ‘a well-honed piece of writing’.
But if the first word ends in ‘ly’, like in ‘a specially designed workshop’, you don’t need a hyphen.
When it comes after the noun, the compound adjective usually doesn’t get a hyphen. So, we say an easy-to-remember number, but the number is easy to remember. Same goes for up to date—if it’s before a noun it needs a hyphen. A document is up to date but it’s an up-to-date document.
After a prefix
If you’re adding a prefix like ‘pre’, ‘un’, ‘non’ or ‘anti’ to a proper adjective (that’s an adjective made from a proper noun [one with a capital letter] like American, Japanese, Victorian), use a hyphen: un-American, non-EC countries. Long-established words like ‘preamble’ and ‘degrade’ don’t need a hyphen as the prefix is seen as fully fused.
Use a hyphen with prefixes or suffixes (such as ‘-like’) when you’ve repeated letters in a word, but you pronounce them separately, as in shell-like or anti-inflammatory. Because shelllike looks weird.
Also use a hyphen if there’s a risk of mispronouncing a word. So, you’d hyphenate co-worker, for example, to stop people tripping up over ‘cow’ when they read it. But coordinator doesn’t need one.
And we hyphenate words that are spelled the same but can have very different meanings or different pronunciations (called homographs, fact-fans) like ‘recreation’ (fun) and ‘re-creation’ (creating again).
Some examples of the difference a hyphen can make:
A man-eating chicken—a chicken that eats humans.
A man eating chicken—a man who’s eating chicken.
She re-covered the sofa—she put a new cover on the sofa.
She recovered the sofa—from where?
Still confused? Follow these two rules.
If you can avoid using a hyphen, do.
If you think there’s any risk of ambiguity, stick one in.
More interesting hyphen stuff: The hyphen is an endangered species in English. In 2007, the sixth edition of the Shorter Oxford English Dictionary removed the hyphens from 16,000 entries including ‘figleaf’, ‘potbelly’ and ‘pigeonhole’.
The Oxford University Press style manual points out that ‘If you take hyphens seriously, you will surely go mad’. So, don't sweat it too much.
Words we don’t hyphenate