Percentage change
The rate of change expressed as a percent of the base value
Core Idea
Percentage change shows how much a value increased or decreased relative to its base value. It is not the same as the raw difference. The key question is always "change compared to what?"
For example, going from 100 to 120 means the raw change is 20, but the percentage change is 20 / 100 = 20%. If the base value changes, the interpretation changes too, even when the raw change stays the same.
When the comparison is about change over time, the same idea is often described as a growth rate. The label changes with the context, but the calculation still depends on the base value.
Why It Matters Here
In Mathbong's NCS numeracy posts, percentage change connects discount, profit-rate, and data-interpretation problems. It also works closely with index number reading, because many problems switch back and forth between relative change and actual values.