A perfect score of 100 is great – but is that written 100%, 100 per cent or 100 percent? I’m all for 100%.
The Style manual for authors, editors and printers (Sixth edition, 2002) noted that the spaced form of per cent is the most commonly used in Australia, but percent is the dominant form in the United States.
Using the % symbol with numerals, particularly in statistically oriented text such as reporting survey results, makes the numbers stand out and makes it easier to compare numbers. The % symbol should always be used in tables.
The Style manual supports this use: “Where numerals are generally being employed for numbers, it is preferable also to show percentages in numerals with the symbol”.
The words per cent or percent are still used as an unnecessary sign of more formal writing, but let’s change that. As always in editing, the aim is to communicate clearly and make it easy for readers to understand the text and the numbers.
So it is not wrong to use the % symbol. But be consistent: don’t use 100 per cent in half your document and 100% in the other half.