The Big Mac PPP exchange rate between two countries is obtained by dividing the price of a Big Mac in one country (in its currency) by the price of a Big Mac in another country (in its currency).
For these reasons, the index enables a comparison between many countries' currencies. The Big Mac was chosen because it is available to a common specification in many countries around the world as local McDonald's franchisees at least in theory have significant responsibility for negotiating input prices. In the Big Mac index, the basket in question is a single Big Mac burger as sold by the McDonald's fast food restaurant chain. One suggested method of predicting exchange rate movements is that the rate between two currencies should naturally adjust so that a sample basket of goods and services should cost the same in both currencies (PPP). The working-time based Big Mac index might give a more realistic view of the purchasing power of the average worker, as it takes into account more factors, such as local wages. UBS Wealth Management Research has expanded the idea of the Big Mac index to include the amount of time that an average worker in a given country must work to earn enough to buy a Big Mac. The index also gave rise to the word burgernomics. The Big Mac index was introduced in The Economist in September 1986 by Pam Woodall as a semi-humorous illustration and has been published by that paper annually since then.