To turn a number into its equivalent percentage, a person should move the decimal point two places to the right and then add the percent sign. For example, to turn the number 7 into a percentage, a person would move the decimal point two places to the right, which requires the addition of two 0s after the 7, and the percentage is expressed as 700 percent. In the case of .35, moving the decimal point two places to the right expresses the number in its percentage form as 35 percent.
Percentage equivalents need not be confined to whole numbers. For example, the number .0572 can be expressed as 5.72 percent. As another example, .0001 becomes .01 percent, which is 1/100 of 1 percent.
The use of percentages in computations existed prior to the invention of the decimal system and can be traced back to Ancient Rome. Taxes levied by the Roman emperor Augustus on certain goods were calculated as 1/100 of the sale amount. These tax computations were similar to the modern tax percentage calculations. The modern term "percent" is derived from the Latin phrase "per centum," which means "by the hundred."
By the Middle Ages, similar calculations based on fractions containing 100 as a denominator were not uncommon. The use of percentages to express interest rates was a standardized practice by the 1600s.