percent is a noun, thus a more accurate translation of it will be tanto por ciento that is also a noun (RAE) and a synonym of porcentaje, another translation of percent. You could also include porciento, another noun that is a synonym of porcentaje, mostly used in the Caribbean. (RAE DPD). You should separate this entry from per cent, and adverb and pair it alone with por ciento, another adverb. I see a lot of people translating percent incorrectly as percent as por ciento without paying attention to this distinction.