Economics
Purchasing Power Parity and the Big Mac Index
Quick fact
The Big Mac Index was introduced by The Economist in 1986 and has been published annually ever since, making it a long-standing, lighthearted economic indicator.
Why this is interesting
Why does a Big Mac cost more in some countries than others? The Big Mac Index turns this familiar burger into a window into global currency economics.
Read the full explanation
Understanding Purchasing Power Parity and the Big Mac Index
Imagine you're traveling and buy a Big Mac in two different countries. If the exchange rate were 'fair', the price should be roughly the same when converted to a common currency, because the burger is essentially the same product. This is the idea behind purchasing power parity (PPP). The Big Mac Index takes this theory literally: it compares the local price of a Big Mac (in local currency) with the US price, then calculates the 'implied' exchange rate. If the actual exchange rate differs, that suggests the currency is undervalued or overvalued. For example, if a Big Mac costs $5 in the US and 10 yuan in China, the implied PPP exchange rate is 2 yuan per dollar. If the actual rate is 6 yuan per dollar, the yuan is considered undervalued by about 67%. This simple comparison makes the abstract concept of PPP tangible and accessible to anyone who has ever ordered a burger.
A deeper explanation
PPP rests on the 'law of one price', which states that identical goods should sell for the same price in different markets after accounting for exchange rates. In theory, if prices differ, arbitrage opportunities would arise—buying cheap and selling where it's expensive—driving prices to converge. However, real-world frictions such as transportation costs, tariffs, and non-tradable inputs (rent, labor) prevent full convergence. The Big Mac Index is therefore a heuristic, not a precise measure. It works because the Big Mac is a globally standardized product, yet its local price reflects local costs and market conditions. By comparing these prices, the index offers a practical and memorable demonstration of PPP's predictions. It also highlights that PPP is a long-run concept; short-run exchange rates are heavily influenced by capital flows and speculation. Thus, the index not only illustrates PPP but also underscores its limitations in the real, messy economy.