What is interest rate parity in simple terms?

If capital can move freely, investing in any currency should give the same return once exchange rate changes are taken into account.

What is the difference between CIP and UIP?

CIP is the parity condition when currency risk is removed with a forward contract; UIP leaves the risk unhedged and uses expectations of the future exchange rate. CIP has generally held well, while UIP often fails in the short run.

Interest Rate Parity

📈 Economics By CampusDown Wiki Editorial Team Last updated October 26, 2026

Interest rate parity is an international finance theory holding that, with free capital mobility, returns on assets denominated in two currencies must be equal once exchange rates are taken into account, so the interest rate differential between two countries equals the forward premium or discount or the expected change in the exchange rate. John Maynard Keynes (1923) set it out systematically.

Contents

1. Covered interest parity (CIP)
2. Uncovered interest parity (UIP) and the forward discount puzzle
3. Carry trades and recent research
4. FAQ
5. References

Covered interest parity (CIP)

Consider an investor comparing two strategies: depositing euros in the euro area for a year, or buying dollars at the spot rate, depositing them in the United States and converting back to euros after a year. If the future exchange rate is locked in today with a forward contract, neither strategy carries currency risk, so the returns must be equal for there to be no arbitrage. This condition is covered interest parity, approximately: forward premium = domestic interest rate − foreign interest rate. In other words, a high-interest currency trades at a forward discount. Keynes (1923) described this relationship in A Tract on Monetary Reform, and Frenkel and Levich (1975) found that once transaction costs are considered, CIP generally holds and little arbitrage profit remains. CIP came to be regarded as one of the most reliable relationships in international finance.

Uncovered interest parity (UIP) and the forward discount puzzle

When currency risk is not hedged with a forward contract, expectations of the future spot rate enter. Under uncovered interest parity, with risk-neutral investors the interest differential equals the expected rate of currency depreciation, so a high-interest currency is expected to depreciate by that amount. Combined with purchasing power parity and the Fisher effect, this relationship became a foundation of exchange rate theory, and Dornbusch's (1976) overshooting model uses UIP as a core assumption. Yet Hansen and Hodrick (1980) and Fama (1984) showed that in actual data high-interest currencies tend not to depreciate as predicted and often appreciate instead, the forward discount or Fama puzzle. Froot and Thaler (1990) and Engel (1996) surveyed attempts to explain it through risk premia or errors in expectations, and Chinn and Meredith (2004) reported that UIP fits better at long horizons.

Carry trades and recent research

The short-run failure of UIP implies that carry trades, borrowing in low-interest currencies to invest in high-interest ones, earn positive returns on average. Brunnermeier, Nagel and Pedersen (2008) argued that these returns compensate for crash risk, steady gains punctuated by sharp losses in crises, and Lustig and Verdelhan (2007) explained the risk premium by the greater exposure of high-interest currencies to consumption growth risk. After the 2008 global financial crisis, even the long-robust CIP broke down systematically. Du, Tepper and Verdelhan (2018) attributed persistent CIP deviations to tighter bank regulation that raised balance sheet costs and constrained arbitrage. Together with the impossible trinity and the term structure of interest rates, interest rate parity is a core framework for analyzing links among monetary policy, capital flows and exchange rates.

FAQ

What is interest rate parity in simple terms?: If capital can move freely, investing in any currency should give the same return once exchange rate changes are taken into account.
What is the difference between CIP and UIP?: CIP is the parity condition when currency risk is removed with a forward contract; UIP leaves the risk unhedged and uses expectations of the future exchange rate. CIP has generally held well, while UIP often fails in the short run.

Sources reviewed: 2026-10-26

References

Keynes, J. M. (1923). A Tract on Monetary Reform. London: Macmillan.
Fisher, I. (1930). The Theory of Interest. New York: Macmillan.
Frenkel, J. A., & Levich, R. M. (1975). Covered interest arbitrage: Unexploited profits? Journal of Political Economy, 83(2), 325–338.
Dornbusch, R. (1976). Expectations and exchange rate dynamics. Journal of Political Economy, 84(6), 1161–1176.
Hansen, L. P., & Hodrick, R. J. (1980). Forward exchange rates as optimal predictors of future spot rates: An econometric analysis. Journal of Political Economy, 88(5), 829–853.
Fama, E. F. (1984). Forward and spot exchange rates. Journal of Monetary Economics, 14(3), 319–338.
Froot, K. A., & Thaler, R. H. (1990). Anomalies: Foreign exchange. Journal of Economic Perspectives, 4(3), 179–192.
Engel, C. (1996). The forward discount anomaly and the risk premium: A survey of recent evidence. Journal of Empirical Finance, 3(2), 123–192.
Taylor, M. P. (1995). The economics of exchange rates. Journal of Economic Literature, 33(1), 13–47.
Chinn, M. D., & Meredith, G. (2004). Monetary policy and long-horizon uncovered interest parity. IMF Staff Papers, 51(3), 409–430.
Brunnermeier, M. K., Nagel, S., & Pedersen, L. H. (2008). Carry trades and currency crashes. NBER Macroeconomics Annual, 23, 313–347.
Lustig, H., & Verdelhan, A. (2007). The cross-section of foreign currency risk premia and consumption growth risk. American Economic Review, 97(1), 89–117.
Du, W., Tepper, A., & Verdelhan, A. (2018). Deviations from covered interest rate parity. Journal of Finance, 73(3), 915–957.

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This article was last updated on October 26, 2026. It is based on widely recognized original works and textbooks; when citing it in a paper, please check the original sources listed in the references.