GrammarPhile Blog

3 Rules for Using Percentages

Posted by Terri Porter   Jan 28, 2016 7:00:00 AM

percent signI’ve had a love affair with words and grammar pretty much my entire life. Math? Not so much. It’s useful, yes. Important too. But having to apply it is like going to the dentist — something I need to do even if I’m less than thrilled about it. So it’s with the greater good in mind that I tackle the use of percent, percentage, percentage points and related questions. You’re welcome.

Percent vs. Percentage

Although some sources (the mercurial Merriam-Webster’s being one of them) suggest that percent and percentage are interchangeable, the more traditional approach is to use percent with a number and percentage with no number:

A surprisingly high percentage of college freshmen drop out.

More than 25 percent of college freshmen drop out.

No style guide that we know of supports using numerals with percentage. For that reason, the following construction is incorrect:

The percentage of college freshman who drop out is higher than 25.

You’d either need to add “percent” at the end of the sentence or rewrite to avoid using “percentage/percent” in the same sentence. The latter approach is preferable but not always possible, as in sports stories. For example:

Tater and Tot had the highest field goal percentages for the night, shooting 63 and 68 percent, respectively.

Percent vs. Percentage Points

Suppose you encounter the following news item:

Interest rates jumped from 6 to 9 percent.

Would you say interest rates increased by 3 percent or by 3 percentage points? The latter is correct. Here’s why …

Percent change is the ratio of two values (the difference between the new value and the old value, divided by the old value). Using the above example, (9-6)/6 = .50. So you could correctly say either of the following:

Interest rates increased by 50 percent.

Interest rates increased by 3 percentage points.

The easy way to remember which term to use is this: If you’re just subtracting one percentage from another (9% – 6%), use percentage points to talk about the difference.

Words vs. Symbols

Whether to spell out percent or use the % symbol is largely a matter of style, as is using numerals versus spelling out the numerical values.

The Chicago Manual of Style, for instance, says that percent is usually used in nontechnical contexts, while % is more common in scientific and statistical copy. Numerals are used in all instances with percent except at the beginning of a sentence.

The AP Stylebook always spells out percent because the symbol doesn’t translate between AP and newspaper computers. It also always uses numerals with percent except at the beginning of a sentence.

Both the AMA and APA style guides say to use % with numerals in all cases except at the beginning of a sentence.

Some clients have their own style. The important point is to apply whatever style you choose consistently.

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Topics: percentage points, percentage, percent, percent sign

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