Which is correct?
Car dealerships and credit-card companies like to advertise “0% interest,” which is understandable enough but mathematically a bit odd. It makes you wonder whether marketers are uncomfortable with an ad that proclaims “No interest!”
The word percent is a 16th-century invention, from the Latin words per and centum, or 100. In the UK, it’s usually written per cent, while Americans in the last few decades have shifted to the closed-up percent.
Either way, it still means “per 100.” That’s useful for expressing a relationship in a standardized way. But zero per 100 is just a longish way of saying zero. There’s nothing wrong with zero percent interest, but careful writers don’t make readers do unnecessary math. Zero interest or no interest are clear ways to get the idea across.
If you must include the zero, style guides offer conflicting advice: zero is normally written out, but numbers with percentages are written as numerals. In the wild, 0 percent slightly leads zero percent. That’s according to Google hits, but news sites are more than twice as likely to write out the word zero. The ask-the-editor columns of The Chicago Manual of Style and the Associated Press Stylebook disagree on the solution: AP says to write out zero percent, while CMOS favors 0 percent using the numeral.
You can avoid the issue by remembering that zero percent—just like zero per million or zero per 14—still means zero, and that’s all you really need to write.
This article was written by Mark Allen, a freelance copy editor who is known as @EditorMark on Twitter.