1560–70; short for Medieval Latin per centum by the hundred. See per, cent

Percent is from the Latin adverbial phrase per centum meaning “by the hundred.” The Latin phrase entered English in the 16th century. Later, it was abbreviated per cent. with a final period. Eventually, the period was dropped and the two parts merged to produce the modern one-word form percent. The two-word form per cent is still used occasionally, but its use is diminishing. The percent sign ( % ) is used chiefly in scientific, tabular, or statistical material and only with numerals preceding it: 58%; a range of 30% to 40%.
In the senses “rate or proportion per hundred” and “proportion in general” percent and percentage are frequently interchangeable. With a preceding number, only percent occurs ( a 16 percent decline ); with no preceding number, either occurs, but percentage is much more common: a certain percentage (or percent ) of the land.