# Covered and Uncovered Interest Parity > Interest rate parity links exchange rates and interest rates. Learn covered and uncovered parity, the arbitrage behind them and the forward premium puzzle. Source: https://learn.tradelabsai.com/forex/interest-rate-parity/ Track: Forex · Level: Advanced · Updated: 2026-10-03 Publisher: TradeLabs AI (https://tradelabsai.com). Education, not financial advice. Cite as: TradeLabs Learn, "Covered and Uncovered Interest Parity", https://learn.tradelabsai.com/forex/interest-rate-parity/ Interest rate parity is the relationship that links spot exchange rates, forward exchange rates and interest rates in two currencies. Its covered form says that forward rates must reflect interest rate differences, or arbitrage would be possible; it holds closely in practice. Its uncovered form says that expected exchange rate changes should offset interest differences, so investors cannot earn more simply by holding higher yielding currencies; in practice, it often fails, which is why carry trades have been profitable on average. ## Covered interest parity (CIP) ``` F / S = (1 + r_quote × T) / (1 + r_base × T) ``` Investing in the domestic currency must give the same return as converting to the foreign currency, investing there and locking in the conversion back with a forward. If not, there is a riskless arbitrage, known as covered interest arbitrage. **Example: Covered interest arbitrage** Spot USD/JPY is 150.00. One year rates: US 5.0%, Japan 0.5%. CIP forward = 150.00 × (1.005 / 1.05) ≈ 143.57. Suppose a dealer quotes the one year forward at 145.00. An arbitrageur: 1. Borrows ¥150,000,000 at 0.5% (owes ¥150,750,000 in a year). 2. Converts to $1,000,000 at spot. 3. Invests the dollars at 5.0%, growing to $1,050,000. 4. Sells $1,050,000 forward at 145.00, locking in ¥152,250,000. Profit: ¥152,250,000 minus ¥150,750,000 = ¥1,500,000, without any exchange rate risk. Trades like this push the forward back towards 143.57. See [Cash-and-Carry Arbitrage](https://learn.tradelabsai.com/futures/cash-and-carry-arbitrage/). Before 2008, CIP held almost exactly for major currencies. Since then, small persistent deviations, measured by the cross currency basis, have appeared because of bank balance sheet constraints and demand for dollar funding. See [Cross-Currency Basis](https://learn.tradelabsai.com/forex/cross-currency-basis/). ## Uncovered interest parity (UIP) UIP drops the forward hedge and says the expected future spot rate should offset the interest difference: ``` expected % change in spot ≈ interest rate difference ``` If US rates are 4.5 points higher than Japanese rates, UIP predicts the dollar should weaken against the yen by about 4.5% a year on average, removing any advantage from holding dollars. ## The forward premium puzzle Many studies, starting with Eugene Fama's 1984 paper, found that UIP fails over short to medium horizons: high interest rate currencies have tended not to depreciate as predicted, and have sometimes appreciated. This is known as the forward premium puzzle. Explanations include: - **Risk premiums:** high yield currencies tend to crash in global downturns, so investors demand extra return. - **Peso problems:** rare large depreciations that may not appear in short samples. - **Slow moving capital and behavioural factors.** This failure is the foundation of the carry trade. See [Carry Trades in Forex](https://learn.tradelabsai.com/forex/carry-trades-in-forex/) and [Carry Factor](https://learn.tradelabsai.com/research/carry-factor/). ## CIP vs UIP | | Covered interest parity | Uncovered interest parity | |---|---|---| | Uses a forward hedge | Yes | No | | Enforced by arbitrage | Yes | No; it is an expectation | | Holds in practice | Closely, with small basis deviations | Often fails over short horizons | | Main use | Pricing forwards and futures | Theory of exchange rate expectations | ## Practical uses - **Pricing forwards and futures:** CIP gives the fair forward rate. See [FX Forwards and Forward Points](https://learn.tradelabsai.com/forex/fx-forwards-and-forward-points/). - **Hedging costs:** CIP shows whether hedging a foreign investment adds or subtracts return. - **Spotting funding stress:** deviations from CIP signal dollar funding pressure. - **Carry strategies:** UIP failures create opportunities, with crash risk. ## Frequently asked questions ### What is interest rate parity? A relationship stating that the difference between forward and spot exchange rates equals the interest rate difference between the two currencies, so returns are equalised. ### What is the difference between covered and uncovered interest parity? Covered parity uses forward contracts to remove currency risk and is enforced by arbitrage; uncovered parity relies on expected exchange rate moves and often fails in practice. ### Why does uncovered interest parity fail? Possible reasons include risk premiums for crash risk, rare large depreciations and behavioural factors, which together allow carry trades to earn returns on average. Next, learn what deviations from covered parity reveal in [Cross-Currency Basis](https://learn.tradelabsai.com/forex/cross-currency-basis/). ## Continue learning - Next lesson: [Cross-Currency Basis](https://learn.tradelabsai.com/forex/cross-currency-basis/) - Previous lesson: [Currency Futures](https://learn.tradelabsai.com/forex/currency-futures/) - Related: [Currency Futures](https://learn.tradelabsai.com/forex/currency-futures/): Currency futures are exchange traded contracts to exchange currencies at a set rate on a future date. Learn CME contract sizes, quotes, margin, rolls and uses. - Related: [FX Forwards and Forward Points](https://learn.tradelabsai.com/forex/fx-forwards-and-forward-points/): An FX forward fixes an exchange rate for a future date. Learn how forward rates and forward points are calculated from interest rates, with examples and uses. - Related: [Cross-Currency Basis](https://learn.tradelabsai.com/forex/cross-currency-basis/): The cross currency basis measures deviations from covered interest parity. Learn why it exists, why it is often negative and what it says about dollar funding. - Related: [Carry Trades in Forex](https://learn.tradelabsai.com/forex/carry-trades-in-forex/): A forex carry trade buys a high yielding currency funded by a low yielding one. Learn how it earns, famous unwinds, funding currencies and how to manage crash risk. - Related: [Interest Rate Differentials](https://learn.tradelabsai.com/forex/interest-rate-differentials/): The gap between two countries' interest rates is a major driver of exchange rates. Learn why differentials move currencies, how to track them and their limits. - Related: [Cash-and-Carry Arbitrage](https://learn.tradelabsai.com/futures/cash-and-carry-arbitrage/): Cash and carry arbitrage buys an asset and sells its futures when futures are rich versus carry costs. Learn the formula, gold, index and crypto examples, and risks.