Things cost more today than they used to. In the 1920's, a loaf of bread cost about a nickel. Today it costs more than \$1.50. In general, over the past 300 years in the United States the overall level of prices has risen from year to year. This phenomenon of rising prices is called inflation.

While small changes in the price level from year to year may not be that noticeable, over time, these small changes add up, leading to big effects. Over the past 70 years, the average rate of inflation in the United States from year to year has been a bit under 5 percent. This small year-to-year inflation level has led to a 30-fold increase in the overall price during that same period.

Inflation plays an important role in the macroeconomic economy by changing the value of a dollar across time. This section on inflation will deal with three important aspects of inflation. First, it will cover how to calculate inflation. Second, it will cover the effects of inflation calculations using the CPI and GDP measures. Third, it will introduce the effects of inflation.

### Calculating inflation

Inflation is the change in the price level from one year to the next. The change in inflation can be calculated by using whatever price index is most applicable to the given situation. The two most common price indices used in calculating inflation are CPI and the GDP deflator. Know, though, that the inflation rates derived from different price indices will themselves be different.

#### Calculating Inflation Using CPI

The price level most commonly used in the United States is the CPI, or consumer price index. Thus, the simplest and most common method of calculating inflation is to calculate the percentage change in the CPI from one year to the next. The CPI is calculated using a fixed basket of goods and services; the percentage change in the CPI therefore tells how much more or less expensive the fixed basket of goods and services in the CPI is from one year to the next. The percentage change in the CPI is also known as the percentage change in the price level or as the inflation rate.

Fortunately, once the CPI has been calculated, the percentage change in the price level is very easy to find. Let us look at the following example of "Country B."