How to Use Apostrophes With Numbers, Letters, Words


Adding s to pluralize numbers and acronums like 401kA New York Times headline about 401(k) investment options prompted me to review guidelines for using an apostrophe when making plurals of letters and numbers:

Pushing Aside 401(k)’s for Mandatory Savings Plans

A quick search led to a headline on about 409(k)s, this one without the apostrophe:

401(k)s: Starting to Invest

There are multiple scenarios that require an apostrophe decision: to add or not to add. Consider these:

When you add an s to a number or numbers to make them plural, you do not need an apostrophe:

She said both size 9s were too small.
Temperatures dropped into the low 20s last night.
There were two 747s sitting on the tarmac.

When you add an s to a single letter to make it plural, you add an apostrophe:

Mind your p’s and q’s.
The Oakland A’s played the Minnesota Twins on Saturday.
He reviewed the contract to be sure he had dotted all the i’s and crossed all the t’s.

Note the confusion that could result if there were not an apostrophe in the second and third examples:

The Oakland As played the Minnesota Twins on Saturday.
(Without the apostrophe, As is a word)
He reviewed the contract to be sure he had dotted all the is and crossed all the ts. (Again, without the apostrophe, is forms a word.)

With multiple letters, don’t use an apostrophe:

She knew her ABCs by the time she started nursery school.
Four VIPs joined Prince Charles in his box at the opera.
Someone vandalized the bank’s downtown ATMs.

When you want to make a word plural, an apostrophe is not necessary:

He cluttered his presentation with too many ands.
Don’t worry about past would-haves and should-haves.
How many pleases does your child say in a day?

There can be exceptions Here’s one:

What are the do’s and don’ts of electronic résumés and cover letters?

Does 401(k) need an apostrophe to make it plural? I suspect the New York Times writer or editor who inserted the apostrophe was following the guideline to add an apostrophe to a single letter.

And the CNN Money writer or editor likely was following the guideline to avoid an apostrophe with multiple numbers.

I don’t consider either one wrong. The Associated Press Stylebook, my preferred resource for punctuation, does not provide a specific guideline related to making 401(k) plural.

Yet as a ruthless editor, I’d be inclined to not insert an apostrophe to make 401(k) plural.

Does your organization follow a style guide? I’ll revisit style guides and their role in a future post. Stay tuned!

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Kathy Watson

Kathy Watson has a love/hate relationship with grammar; she loves words and the punctuation that helps them make sense, yet she hates those pesky rules. A self-proclaimed ruthless editor, she prefers standard usage guidelines of The Associated Press Stylebook. Her easy-to-use Grammar for People Who Hate Rules helps people write and speak with authority and confidence. She encourages and welcomes questions and comments. (Email)