An economic theory stating that exchange rates should adjust so that identical goods cost the same in different countries when priced in a common currency. PPP provides a long-term benchmark for assessing whether currencies are overvalued or undervalued.
How PPP Works
Purchasing power parity is based on the law of one price: in an efficient market, identical goods should sell for the same price everywhere when converted to a common currency. If a basket of goods costs $100 in the U.S. and 90 EUR in Europe, PPP suggests the fair exchange rate should be approximately 1.11 USD/EUR.
PPP as a Valuation Tool
When the actual exchange rate deviates significantly from the PPP rate, the currency may be considered overvalued or undervalued. The OECD publishes PPP exchange rates annually, and traders use them as a long-term anchor for currency analysis.
PPP works best over long time horizons (5-10 years). In the short term, exchange rates are driven by Interest Rate Differential differences, Capital Flow, and market sentiment, which can keep currencies away from PPP for extended periods. The Big Mac Index is a simplified, popular version of PPP comparison.
Limitations
PPP does not account for non-tradable goods (haircuts, rent), trade barriers, transportation costs, or differences in product quality. It is a theoretical benchmark, not a short-term trading signal.
Related Terms
Big Mac Index
An informal measure of purchasing power parity created by The Economist magazine, comparing the price of a McDonald's Big Mac across countries to estimate whether currencies are overvalued or undervalued against the dollar.
Exchange Rate
The price of one currency expressed in terms of another currency. EUR/USD at 1.0850 means 1 euro equals 1.0850 US dollars.
Inflation
A sustained increase in the general price level of goods and services, reducing purchasing power. Central banks target specific inflation rates (typically 2%) and adjust monetary policy to achieve that target.
Interest Rate Parity (IRP)
An economic theory stating that the difference in interest rates between two countries should equal the difference between the forward and spot exchange rates. IRP ensures no arbitrage opportunity exists between currency and interest rate markets.
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