Shares of energy firms in the index declined 1.6% as oil prices slumped (source)

I somehow feel like there should be a preposition after "declined" marking the degree of the decline. Shouldn't it be "declined by 1.6%"? For example, I would write:

Stocks declined by 20%.

Google seems to suggest that both are common. However, it also seems that some of the search results are headlines or false positives, which makes it hard to tell which one is correct/idiomatic. Is the preposition "by" needed/optional? Is there a difference in meaning?

What about

Stocks fell 20%
Stocks fell by 20%

  • 1
    If you go to Google and click on the News tab, then search for "declined 20 percent", you'll get plenty of bona fide results.
    – user3395
    Oct 20, 2018 at 1:17

1 Answer 1


I think you are right in that Stocks fell by 20% and Stocks declined by 20% are a little more common in the business world and might seem more natural to the ear. When it comes to reporting the numbers in business, people appreciate clarity, and adding the "by" could be seen as being a little clearer. But as @userr2684291 says, it is still correct and common to omit the "by."

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