The Big Mac Index at 40 Is More Metaphor Than Measure

When you travel abroad, at some point you have probably had the same reaction as many other travellers: how can things be so expensive, or so cheap? Go out for pizza in Zurich or a beer in Oslo, and prices may feel startlingly high. Try buying a cup of coffee in Mexico City or a souvenir in Buenos Aires, and they may seem surprisingly low.

Exchange-rate economics is complex, but a substantial body of research finds that, over the longer term, exchange rates are anchored by relative price levels. This idea is embodied in purchasing power parity theory, which states that the exchange rate is proportional to the ratio of price levels in two countries.

Official PPP measures used by the World Bank, IMF and OECD for comparing real GDP and living standards still rely on the same underlying logic: market rates undervalue the domestic purchasing power of many emerging-market currencies. India’s economy looks larger on a PPP basis precisely because local services, food and labour are cheaper. That does not mean the rupee can buy the same volume of imported oil, service the same amount of dollar debt or purchase the same quantity of foreign capital goods.

Absolute PPP, under which identical goods should cost the same after conversion into a common currency, is a useful long-run conceptual anchor, not a short-term trading signal. Deviations can persist for years because of capital flows, interest-rate differentials, policy, risk premia and the Balassa-Samuelson effect, under which richer economies tend to have higher prices for non-tradable goods and services. Relative PPP, which holds that exchange-rate changes should broadly track inflation differentials, is also only a rough, long-horizon guide.

Burger Logic
A simple way of making PPP comparisons was introduced in 1986 by The Economist. The index was first published in September 1986, so 2026 marks its 40th anniversary.

The choice of McDonald’s was grounded in the company’s global reach. It serves close to 70 million people a day in more than 100 countries. In the 2023 Forbes Global 2000 ranking, McDonald’s retained its position as the world’s largest restaurant chain by revenue, with sales of about $23.4 billion and a market value of $216.5 billion.

The Big Mac is also mostly produced to the same specifications across the world. In theory, therefore, the cost of producing it should be reasonably comparable across markets.

The inputs involved in producing a Big Mac span several parts of the local economy, including advertising, agriculture, transport and labour. The burger could therefore be considered much closer to a “basket of goods” than it appears. Although economists usually use a broader basket to determine purchasing power, a burger comes surprisingly close.

The index has also evolved. In 2011, The Economist introduced an alternative version adjusted for GDP per capita, addressing the tendency of the original index to make currencies in poorer countries appear systematically undervalued.

In July 2022, it was further updated to use the US price supplied by McDonald’s as its reference point. The methodology for the GDP-adjusted index was also revised to incorporate the IMF’s historical GDP data. In keeping with the culinary theme, this adjusted measure is referred to as the “gourmet version”.

By plotting a line of best fit between GDP per capita and the price of a Big Mac, the adjusted index seeks to provide a more realistic estimate of a currency’s fair value.

The approach has inspired other single-product comparisons. The Starbucks Index, also known as the Tall Latte Index, was originally popularised by The Wall Street Journal and later tracked by The Economist. It compares the local price of a standard tall latte across countries. Like the Big Mac, a Starbucks coffee combines a globally recognised brand with heavy local non-tradable inputs, including store rent, local labour and utilities.

The iPhone index, by contrast, reflects the quality of local infrastructure required to produce high-technology and luxury goods, revealing a different set of comparisons.

Useful Limits
The law of one price is expected to hold only when homogeneous goods are traded freely and without cost across countries. Although the Big Mac may be regarded as a broadly homogeneous good, it cannot be regarded as a freely traded one.

Many of its ingredients are sourced globally through McDonald’s supply chain. Yet a large share of the cost of producing a Big Mac, including wages, rents and utilities, is location-specific (Parsley and Wei, 2007, 2008).

Trade barriers, taxes and subsidies can also distort prices in ways that are not directly related to currency valuation. Differences in productivity and income levels add another layer of distortion. The resulting price gap may therefore reflect structural features of an economy rather than currency “mispricing” that traders can exploit.

Another major limitation is that the Big Mac is not a perfectly standardised product across countries. Local tastes, ingredients and production methods can vary, affecting the final price. In some countries, McDonald’s positions itself as a premium brand; in others, it is considered a budget option.

The index is also heavily influenced by labour costs in each country and measures the effect those costs have on PPP. That bias helps explain why many emerging-market currencies appear undervalued on the index.

Over the long run, PPP can provide a broad anchor for exchange rates. Allowing for the limitations of a non-traded good, Big Mac prices may also display some tendency towards convergence. That does not, however, give the index reliable forecasting power, irrespective of how far a currency appears to have moved from its long-run norm.

Consider, for example, the real effective exchange rate measures computed by the BIS. Like the Big Mac Index, movements in the BIS indices are highly persistent: highly valued currencies tend to remain highly valued, while low-valued currencies tend to stay low-valued. Measures of persistence for the Big Mac Index are similar in magnitude to those derived from the more comprehensive BIS measures.

That persistence is precisely what limits the index’s usefulness as a market signal. A currency shown as undervalued can remain so for years, offering little guidance on either the timing or direction of its next move.

The index endures because its branding is clever and its intuition memorable. It makes PPP tangible, but it does not make it precise. Forty years on, the Big Mac Index remains more metaphor than measure: a fast-food illustration that explains an economic theory but can mislead when treated as market reality. Economists, policymakers and investors should regard it as a teaching device, not a valuation model.