Calculating Percent Change

Change: 18.00 − 15.00 = 3.00 18.00 - 15.00 = 3.00 18.00 − 15.00 = 3.00
Divide by the original: 3.00 15.00 = 0.20 \frac{3.00}{15.00} = 0.20 15.00 3.00 ​ = 0.20
Convert to a percent: 0.20 × 100 % = 20 % 0.20 \times 100\% = 20\% 0.20 × 100% = 20%

Introduction

Welcome to Percentages in News and Statistics, the fourth course in your learning path! By now you have built a solid foundation: you can convert between percents, decimals, and fractions, handle discounts and taxes, and work with simple and compound interest. That is an impressive toolkit. In this course, we shift our focus to how percentages appear in the real world of news headlines, survey results, and everyday data. This first lesson introduces one of the most common uses of percentages you will encounter in reports and daily life: percent increase and percent decrease. By the end, you will be able to look at any pair of "before" and "after" values and calculate exactly how much something went up or down in percentage terms.

Imagine you read that a city's average rent rose from $1,200 to $1,260 per month. The dollar change is easy to find, but is a $60 jump a big deal or a small one? On a $1,200 rent it might feel modest, yet the same $60 increase on a $300 rent would be enormous. Percent change gives us a single number that captures the size of a change relative to where we started. That is why news articles, economists, and employers all rely on it: it puts changes on an equal footing so we can compare them fairly. Whenever you see a headline like "Gas prices up 8%," the writer used exactly the technique you are about to learn.

\text{Percent Change} = \frac{\text{New Value} - \text{Original Value}}{\text{Original Value}} \times 100\%

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