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.
How Interest Rate Parity Works
Interest rate parity links the forex spot market, forward market, and interest rate markets. If a country offers higher interest rates, its currency should trade at a forward discount (be expected to depreciate) by an amount that offsets the interest rate advantage. This prevents investors from earning risk-free profits by borrowing in one currency and lending in another.
Covered vs. Uncovered IRP
Covered interest rate parity (CIP) uses forward contracts to eliminate exchange rate risk and holds very tightly in practice due to arbitrage. If CIP is violated, institutional traders quickly exploit the discrepancy. Uncovered interest rate parity (UIP) assumes the expected future spot rate will offset the Interest Rate Differential, but this version frequently fails in practice because currencies can trend for years.
The failure of uncovered IRP is precisely what makes the Carry Trade profitable: high-yielding currencies often appreciate rather than depreciate as the theory predicts.
Practical Implications
IRP determines the forward exchange rate used in forex forward contracts and swaps. Understanding IRP helps traders evaluate whether forward points represent fair value or an opportunity.
Related Terms
Interest Rate Differential
The difference in interest rates between two countries or currencies. Interest rate differentials are one of the primary drivers of exchange rate movements and form the basis of carry trade strategies.
Purchasing Power Parity (PPP)
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.
Carry Trade
A strategy where a trader borrows in a low-interest-rate currency and invests in a higher-interest-rate currency to capture the interest rate differential. Carry trades profit from both the rate spread and potential currency appreciation.
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.
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