The general guideline is to use the percentage symbol with numerals and to use the word percent with spelled-out numbers. Section 1.4. 1 of the MLA Handbook offers further guidance on when to use numerals and when to spell out numbers in your work.

Do you write percentages in words?

Words and Numbers

As with any numbers, percentages can be written as either words or numbers: ... Numbers up to ten are usually written as words, while larger numbers are written as numerals. When a percentage is written as a word, it should be followed by “percent”

What is the correct way to write percentage?

Use the symbol % to express percent in scientific and technical writing, except when writing numbers at the beginning of a sentence. When you write out the word, use the form percent instead of the older form per cent.