What's the highest inflation rate in U.S. history?

Inflation is the rate at which the general level of prices for goods and services rises and results in a decrease in purchasing power of a country's currency.

Inflation is calculated using the yearly change in the consumer price index (CPI), which was first introduced in 1913. CPI data before 1913 is estimated using a variety of methods and sources.

Since the founding of the United States in 1776, the highest year-over-year inflation rate observed was 29.78 percent in 1778. In the period of time since the introduction of the CPI, the highest inflation rate observed was 19.66 percent in 1917.

Year-over-year inflation is calculated by subtracting the value of the CPI at the beginning of the year, and subtracting the value at the end of the year. This result is divided by the value of the CPI at the beginning of the year and multiplied by 100. CPI data since its formal introduction as an index has been widely viewed as an accurate description of consumer prices in the United States. CPI data before 1913 is more problematic due to under-reporting, over-reporting, lack of data and different reporting standards utilized.

Before the introduction of the U.S. Federal Reserve by the Federal Reserve Act in 1913, the U.S. economy grew in fits and starts. Periods of rapid inflation and growth in asset prices were followed by severe shocks and panics. Between 1775 and 1913, the United States experienced four separate periods of double-digit inflation.

The U.S. Federal Reserve is mandated to act in an effort to moderate inflation using policy measures where it will intervene in currency, debt and equity markets to achieve this goal. Since the 1980s, the United States has enjoyed a lengthy period of low inflation, with U.S. Federal Reserve chairs often noting concerns regarding deflation rather than inflation. In the years following the 2008 financial crisis, the Fed has kept interest rates at historically-low levels and initiated a bond-buying program (since discontinued) known as quantitative easing to help stimulate the economy – although not without its share of outspoken critics.