In Ancient Rome, long before the existence of the decimal system, computations were often made in fractions which were multiples of 1/100. For example Caesar Augustus levied a tax of 1/100 on goods sold at auction known as centesima rerum venalium. Computation with these fractions was similar to computing percentages. As denominations of money grew in the Middle Ages, computations with a denominator of 100 become more standard and from the late 15th century to the early 16th century it became common for arithmetic texts to include such computations. Many of these texts applied these methods to profit and loss, interest rates, and the Rule of Three. By the 17th century it was standard to quote interest rates in hundredths.

The word percent comes from the Latin phrase per centum meaning by the hundred or for every hundred or out of 100. For example, suppose that a school has exactly 100 students, 50 males and 50 females. You can say that 50 out of 100 students are males or you can shorten it to simply 50 percent.

Any amount can be written as either a percent, or a fraction or decimal. A percent can be reduced, added, subtracted, multiplied, and divided like any fraction or decimal.