Q. Hi, CMOS editors: Would you hyphenate “five times” in “a five times increase”? And if so, would it be “five-times” or “five-time”?
A. We would write “a fivefold increase,” assuming you mean to say that something has grown by a factor of five (e.g., increasing from 10 to 50). And though you could say instead that this same thing grew to five times the original amount, “five times” isn’t normally used as a modifier in the way that “fivefold” is; “five-time increase” won’t work either, unless you mean that something increased on five separate occasions (which says nothing about how much it increased overall).
Another thing to keep in mind: A fivefold increase is 500 percent of the original, but it’s only a 400 percent increase, not a 500 percent increase. For example, 50 is 500 percent of 10 (or five times as much), but that’s an increase of only 40, which is 400 percent of the original 10.