Calculate percentages without guessing
Percentages describe a part of a whole using a scale of 100. Use the first tab to find a percentage of an amount, such as 15% of 200. The second tab tells you what percentage one value represents of another. The third compares an old value with a new value and shows the increase or decrease.
Where percentages are useful
A discount, a change in enrollment, or a share of a total may all use percentages, but the starting value matters. A move from 100 to 120 is a 20% increase because 100 is the starting point. Returning from 120 to 100 is a 16.67% decrease because the starting point is now 120. These changes do not cancel each other as percentages.
Check the denominator
For “what percent” and “percent change,” the second value or old value cannot be zero. The calculator flags that case instead of producing an undefined result. When reporting a percentage, include the original numbers so readers can see what was compared.