From a Burger to an Economic Theory
In September 1986, Economist journalist Pam Woodall was looking for a way to explain a dense exchange-rate theory to ordinary readers without losing them in graphs and formulas. Her solution was both simple and durable: use a product sold in nearly identical form almost everywhere in the world — McDonald's Big Mac — as a ruler for comparing currencies. Ever since, The Economist has published what it calls the "Big Mac Index," and over time it grew into something economists half-jokingly call "burgernomics."
What Is Purchasing Power Parity?
The theory behind the index is purchasing power parity (PPP): the idea that, over the long run, exchange rates should move toward a level where an identical basket of goods costs the same amount in any two countries. If a product is cheap in one country and expensive in another once converted into a common currency, that gap suggests the exchange rate has drifted from its "true" value. PPP had been debated by economists for over a century, but explaining it required complex baskets of goods that were hard to compare across countries. Woodall's trick was to shrink that basket down to a single, universally recognizable item.
Why a Burger?
A Big Mac is manufactured to a largely standard recipe — bun, patty, cheese, lettuce, pickles, special sauce — in roughly 120 countries, so its ingredients barely vary from place to place. Its price also bakes in local rent, wages, electricity, and packaging costs, which makes it a rough proxy for a country's broader cost structure, not just a food price. In a world where building a genuinely comparable consumer basket is difficult and expensive, one product made almost identically everywhere offers a fast, if crude, comparison.
How the Index Is Calculated
The method is straightforward. The Economist collects the local-currency price of a Big Mac from McDonald's outlets around the world, converts each price into US dollars at the current market exchange rate, and compares the result to the average Big Mac price in the United States.
A Worked Example
Suppose a Big Mac costs $5 in the US, but in another country it costs the equivalent of $4 once converted. That currency is then considered roughly 20% "undervalued" by the index — the current exchange rate doesn't fully reflect the price gap, and PPP theory predicts the currency should appreciate over time. If the local price converts to more than $5, the currency is judged "overvalued."
The GDP-Adjusted Version
The index's most common criticism is that it compares rich and poor countries on the same line, even though labor costs are naturally lower in poorer economies, which pulls local prices down. To address this, The Economist has published a "GDP-adjusted" version since 2011. It statistically models the expected relationship between a country's per-capita income and its Big Mac price, then measures how far a currency deviates from that expected line — allowing countries as different as Vietnam and Norway to be compared on a basis adjusted for income level, not just raw price.
What the Index Actually Shows
Over the decades, the index has revealed some consistent patterns. Wealthy, high-income economies like Switzerland and Norway tend to show up as "overvalued," while emerging-market currencies frequently appear "undervalued." This isn't random: it reflects what economists call the Balassa-Samuelson effect — in richer countries, high productivity in tradable sectors drives up wages economy-wide, which raises the price of non-tradable services like rent and labor, and therefore the price of a burger.
Limitations and Criticism
Neither the index's creators nor its users have ever claimed it is a precise measurement tool. A Big Mac's price is shaped by far more than beef, bread, and lettuce — local rents, taxes, labor costs, competitive pressure, and McDonald's own market-specific pricing strategy all play a role. Import tariffs on beef, or cultural and religious dietary norms (in India, for instance, the Big Mac is made with chicken rather than beef and sold as the "Maharaja Mac"), complicate direct comparisons further. Exchange rates themselves are driven by interest rates, capital flows, political risk, and central-bank policy — far more than the price of a fast-food sandwich. Economists generally treat the index as an illustrative teaching tool rather than a serious forecasting instrument, and no one seriously recommends basing investment decisions on it alone.
The Legacy of Burgernomics
What began as a semi-serious experiment now appears in central-bank reports and university economics textbooks. The Economist still updates the index twice a year, in January and July, and it remains a frequently cited illustration of purchasing power parity in academic work. Its success inspired imitators — a Starbucks "tall latte index" and even iPhone-price comparisons have been floated — but none achieved the same staying power. Woodall's decades-old shortcut, reducing one of economics' most abstract ideas to a product everyone recognizes, remains one of the most enduring examples of popular economic explanation.