Percentage

Percentage is a method of expressing a number by comparing it to one hundred. When something is said to be 25 percent, it means 25 out of 100, equivalent to the fraction 25/100 or the decimal 0.25. The standard symbol used is %.

Percentages are used to simplify comparison of numbers that have different bases. For example, 18 students out of 40 and 30 students out of 75 cannot be compared directly, but when converted to percentages—45% and 40%—the comparison becomes clear.

How to calculate

The basic method is to divide the part by the total, then multiply the result by 100. If the part is 12 and the total is 50, the calculation is (12 ÷ 50) × 100 = 24%. Similarly, when a percentage and total are known, the part can be found by multiplying the percentage by the total and then dividing by 100.

Increase and decrease

Percentage change is calculated by finding the difference between the new value and the old value, then dividing by the old value. If a value rises from 200 to 250, the increase is 25%. Decrease is calculated in the same way, but the result is negative or described as a decline.

Common confusion

It is important to distinguish between 'percentage points' and 'percentage change'. If a rate rises from 4% to 6%, this is an increase of two percentage points, but it is also a 50% increase relative to the previous rate. Similarly, a percentage increase and a percentage decrease of the same amount do not cancel out: a value that increases by 50% and then decreases by 50% does not return to its original level.

Uses

Percentages are widely used in finance (interest, taxes, price changes), statistics (election results, employment, disease rates), and health research. They are also related to similar concepts such as per mille (‰), used for very small numbers.