Interest Rate Parity

Last updated on 09/12/2021 1 By indiafreenotes

Interest rate parity (IRP) is a theory according to which the interest rate differential between two countries is equal to the differential between the forward exchange rate and the spot exchange rate.

Interest rate parity is a no-arbitrage condition representing an equilibrium state under which investors interest rates available on bank deposits in two countries. The fact that this condition does not always hold allows for potential opportunities to earn riskless profits from covered interest arbitrage. Two assumptions central to interest rate parity are capital mobility and perfect substitutability of domestic and foreign assets. Given foreign exchange market equilibrium, the interest rate parity condition implies that the expected return on domestic assets will equal the exchange rate-adjusted expected return on foreign currency assets. Investors then cannot earn arbitrage profits by borrowing in a country with a lower interest rate, exchanging for foreign currency, and investing in a foreign country with a higher interest rate, due to gains or losses from exchanging back to their domestic currency at maturity. Interest rate parity takes on two distinctive forms: uncovered interest rate parity refers to the parity condition in which exposure to foreign exchange risk (unanticipated changes in exchange rates) is uninhibited, whereas covered interest rate parity refers to the condition in which a forward contract has been used to cover (eliminate exposure to) exchange rate risk. Each form of the parity condition demonstrates a unique relationship with implications for the forecasting of future exchange rates: the forward exchange rate and the future spot exchange rate.

Economists have found empirical evidence that covered interest rate parity generally holds, though not with precision due to the effects of various risks, costs, taxation, and ultimate differences in liquidity. When both covered and uncovered interest rate parity hold, they expose a relationship suggesting that the forward rate is an unbiased predictor of the future spot rate. This relationship can be employed to test whether uncovered interest rate parity holds, for which economists have found mixed results. When uncovered interest rate parity and purchasing power parity hold together, they illuminate a relationship named real interest rate parity, which suggests that expected real interest rates represent expected adjustments in the real exchange rate. This relationship generally holds strongly over longer terms and among emerging market countries.

Interest rate parity (IRP) plays an essential role in foreign exchange markets by connecting interest rates, spot exchange rates, and foreign exchange rates.

IRP is the fundamental equation that governs the relationship between interest rates and currency exchange rates. The basic premise of IRP is that hedged returns from investing in different currencies should be the same, regardless of their interest rates.

IRP is the concept of no-arbitrage in the foreign exchange markets (the simultaneous purchase and sale of an asset to profit from a difference in the price). Investors cannot lock in the current exchange rate in one currency for a lower price and then purchase another currency from a country offering a higher interest rate.

The formula for IRP is:

where:

F0 = Forward Rate

S0 = Spot Rate

ic = Interest rate in country c

ib =Interest rate in country b

Assumptions

Interest rate parity rests on certain assumptions, the first being that capital is mobile – investors can readily exchange domestic assets for foreign assets. The second assumption is that assets have perfect substitutability, following from their similarities in riskiness and liquidity. Given capital mobility and perfect substitutability, investors would be expected to hold those assets offering greater returns, be they domestic or foreign assets. However, both domestic and foreign assets are held by investors. Therefore, it must be true that no difference can exist between the returns on domestic assets and the returns on foreign assets. That is not to say that domestic investors and foreign investors will earn equivalent returns, but that a single investor on any given side would expect to earn equivalent returns from either investment decision.

Important

Interest rate parity is an important concept. If the interest rate parity relationship does not hold true, then you could make a riskless profit. The situation where IRP does not hold would allow for the use of an arbitrage strategy. For example, let us look at the scenario where the forward exchange rate is not in equilibrium with the spot exchange rate.

If the actual forward exchange rate is higher than the IRP forward exchange rate, then you could make an arbitrage profit. To do this, you would borrow money, exchange it at the spot rate, invest at the foreign interest rate and lock in the forward contract. At maturity of the forward contract, you would exchange the money back into your home currency and pay back the money you borrowed. If the forward price you locked in was higher than the IRP equilibrium forward price, then you would have more than the amount you must pay back. You have essentially made riskless money with nothing but borrowed funds.

Interest rate parity is also important in understanding exchange rate determination. Based on the IRP equation, we can see how changing the interest rate can affect what we would expect the spot rate to be at a later date. For example, by holding the foreign country interest rate steady and increasing the home country’s interest rate, we would expect the home country currency to appreciate in relation to the foreign currency. This would affect the expected exchange rate.