Interest Rate Parity

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Definition of 'Interest Rate Parity'

Interest rate parity (IRP) is a theory in international finance that states that the difference in interest rates between two countries is equal to the difference in the exchange rates between their currencies. In other words, if the interest rate on a one-year deposit in the United States is 5% and the interest rate on a one-year deposit in the United Kingdom is 4%, then the exchange rate between the U.S. dollar and the British pound should be £1 = \$1.02.

There are a few reasons why IRP might not hold in practice. First, there are transaction costs involved in converting one currency into another. Second, investors may be willing to accept a lower interest rate in one country in order to avoid the risk of currency fluctuations. Third, governments may intervene in the foreign exchange market to prevent the exchange rate from moving too far from its equilibrium level.

Despite these limitations, IRP is a useful concept for understanding the relationship between interest rates and exchange rates. It can be used to forecast future exchange rates and to make decisions about international investments.

* IRP is based on the law of one price, which states that identical goods should sell for the same price in different markets. In the case of IRP, the law of one price implies that a U.S. dollar should be worth the same amount of goods in the United States and the United Kingdom.
* The interest rate differential between two countries is the difference in the interest rates on one-year deposits in those countries.
* The exchange rate between two currencies is the price of one currency in terms of the other.
* IRP can be expressed as follows:

```
(1 + r1) / (1 + r2) = E(S1 / S2)
```

where r1 is the interest rate in the United States, r2 is the interest rate in the United Kingdom, and E(S1 / S2) is the expected future exchange rate between the U.S. dollar and the British pound.

* If IRP holds, then the exchange rate between the U.S. dollar and the British pound will be equal to the ratio of the interest rates in the two countries.
* If IRP does not hold, then the exchange rate will be different from the ratio of the interest rates.

IRP is a useful concept for understanding the relationship between interest rates and exchange rates. However, it is important to remember that IRP does not always hold in practice.

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