Dictionary.com Word FAQs
Should I write per cent or percent?
Each person should choose a dictionary that will serve as a general guide for spelling and punctuation. By following one dictionary for these matters, your writing will be more consistent. Per cent is the way the phrase was originally written (c. 1568), literally meaning 'by the hundred' and it was written with a period after it - per cent. - as an abbreviation of per centum. The one-word form, percent, is a US creation which was first used around 1883. You will not find many people writing this as two words nowadays.