If you just googled “When to use percent or percentage,” you’ve come to the right place. Here’s what you need to know:
“Percent” and “percentage” are sometimes used interchangeably, especially when people are speaking informally. But these words actually have slightly different meanings (“percent” is one part of a hundred; “percentage” is a part of a whole) and are different parts of speech; “percent” is an adverb and “percentage” is a noun.
The Chicago Manual of Style, 17th Edition, our preferred style guide (mainly because anything over 1,100 pages must be right), has this to say on the issue:
“Despite changing usage, Chicago continues to regard percent as an adverb (“per, or out of, each hundred,” as in 10 percent of the class)—or, less commonly, an adjective (a 10 percent raise)—and to use percentage as the noun form (a significant percentage of her income). The symbol %, however, may stand for either word.” (3.82)
In summary: Use percent with a number and percentage with no number. For example:
- A surprisingly high percentage of people are bored by grammar.
- More than 45 percent of people think 1,100 pages is too long for any book.
We don’t know of any style guides that prescribe using numerals with percentage. So don’t write anything like this:
- The percentage of people who google “Is The Chicago Manual of Style really from Chicago” is higher than 23, a statistic we made up on the spot.
You’d either need to add “percent” at the end of the sentence or rewrite it to avoid using “percentage/percent” in the same sentence. But sometimes, using both in a sentence is unavoidable, as in this example:
- Diddle and Dumpling had the highest field goal percentages for the night, shooting 43 and 48 percent, respectively.
Percent vs. Percentage Points
Maybe you’re writing about interest rates that jumped from 6 to 9 percent (ouch). Would you say interest rates increased by 3 percent or by 3 percentage points? The second is correct. Here’s why:
A percent change is the ratio of two values (the difference between the new value and the old value, divided by the old value; this is because we’re trying to find out (1) how much more or less the new value is compared to the old value and (2) what fraction of the old value the difference is). 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, use percentage points to talk about the difference.
Also, we’re sorry for lots of math in a grammar blog. Atrocious, we know, but it really does add up.
Numbers vs. Numerals
There are three simple rules to guide you when deciding when to spell out numbers before percentages or use numerals:
- Write percentages as numerals…
- …except at the beginning of a sentence.
- Don’t use any space between the numeral and the % symbol.
Writing Percent or the % Symbol
Remember that the % symbol can stand for either “percent” or “percentage.”
If you’re not writing technical content, the word “percent” is generally used; in scientific and statistical copy, the % symbol is more common.
Hyphenating Percent in Compounds
The only time you need to hyphenate a percent is in number ranges. Otherwise, leave compounds open, as in:
- 8 percent
- A 13 percent increase
- A 50–70 percent decrease (CMOS, 7.89 section 1)
AP, AMA, APA and Other Style Guides
Different strokes for different folks…and style guides. Since other people have different takes, here’s a quick overview of some popular style guide approaches:
- AP: Always spell out “percent” because the symbol doesn’t translate between AP and newspaper computers. Always use numerals with “percent” except at the beginning of a sentence.
- AMA: Use numerals and the percent symbol for specific percentages, with no space between the numeral and the symbol. Spell out the numeral and the word “percent” at the beginning of sentences.
- APA: Use “percentage” when there’s no numeral (e.g., 5.2% versus “a high percentage”). Use numerals paired with a percent symbol in table headings, figure labels, and legends as well.
- You: Do whatever you want, as long as it’s clear, consistent, and concise.
This post is an updated version of 3 Rules for Using Percentages by ProofreadNOW.com’s Terri Porter.
