Keep this page as a quick reference when a percentage problem uses a different base or comparison value.
Percentage of a number
Formula: base × percentage ÷ 100. Example: 25% of 80 is 20.
Percentage change
Formula: (new value − original value) ÷ original value × 100. Example: moving from 80 to 100 is a 25% increase.
Discount and error
A discount subtracts a percentage of the original price. Percentage error compares the absolute difference with a reference value. Keep the reference value visible so the result is not misread.
- Name the original value.
- Do not confuse percentage points with percentage change.
- Round only after calculating the full result.
Frequently asked questions
What value is the base?
The base is the value the percentage is applied to. In percentage change, it is usually the original value.