The general guideline is to use the percentage symbol with numerals and to use the word percent with spelled-out numbers.
In statistical copy that calls for frequent use of numbers, it’s appropriate to use numerals, and so the percentage symbol would be used, as in the following example, drawn from a report on a census of language enrollments:
Japanese enrollments increased by 3.1%, from 66,771 in 2013 to 68,810 in 2016; Korean enrollments increased by 13.7%, from 12,256 in 2013 to 13,936 in 2016. (Looney and Lusin 3)
In prose that does not make extensive use of numbers, as in the example below,
Published 14 November 2018