In 2023, the United States accounted for 15.56 percent of global gross domestic product (GDP) after adjusting for purchasing power parity (PPP). This share was expected to decrease to 14.72 percent by 2029, which is roughly a seventh of the global total. What is PPP? The easiest way to understand purchasing power parity is the Big Mac Index, a measure developed by The Economist. The index tracks the price of the McDonald’s Big Mac burger, sold at each of its thousands of restaurants worldwide. Countries where the Big Mac is most expensive have higher purchasing power, meaning one can buy more for each unit of that currency. To calculate PPP, economists use a group of goods to calculate the ratio of the price of this group in each country. This ratio is then used to convert all countries into a standardized price level, on parity with each other. Why use PPP? A U.S. dollar in the United States does not have the same purchasing power as a dollar in China, even after considering the exchange rate. For this reason, adjusting for PPP gives an idea of what the rest of the world could buy in the United States, if prices were the same as in their home country. However, some economists argue that using PPP for comparisons between countries is inaccurate because it changes the price level differently for each country. Still, because it accounts not only for country-specific effects but also inflation and exchange rate fluctuations, PPP is a very popular metric.