Covered Interest Parity

Covered interest parity (CIP) is the no-arbitrage condition under which investing in one currency should produce the same maturity value as converting into another currency, investing there, and locking the return conversion with an FX forward. The currency exposure is “covered” because the future exchange rate is contracted at the start.

Key Takeaways

• CIP compares two funded and fully hedged cash-flow paths with the same start and maturity dates.
• The spot quote, forward quote, interest rates, compounding, transaction sides, and calendars must all be consistent.
• Under frictionless assumptions, the interest-rate differential is offset by the forward premium or discount.
• Real-world CIP deviations can persist because funding, hedging demand, credit, liquidity, collateral, and bank balance-sheet capacity are costly.
• A measured gap is not automatically an executable, risk-free arbitrage.

Covered Interest Parity Formula

Assume the exchange rate is quoted as domestic-currency units per unit of foreign currency:

S = domestic currency / foreign currency

Let:

• S = spot rate;
• F = forward rate for the same pair and maturity;
• r_d = domestic interest rate;
• r_f = foreign interest rate; and
• T = time in years.

With simple interest:

1 + r_d x T = (1 + r_f x T) x F / S

Rearranging:

F = S x (1 + r_d x T) / (1 + r_f x T)

For one-year annual effective rates, the T terms drop out. If the pair is quoted in the opposite direction, the formula must be inverted. Professional calculations commonly use discount factors for exact dates rather than simplified annual rates.

The Two Covered Paths

The diagram uses a simplified one-year CAD/USD example and excludes spreads, fees, credit, taxes, and collateral costs.

    flowchart LR
	    A["Start: CAD 1,000,000 today"]
	    A --> B["Domestic path: invest CAD at 4%"]
	    B --> C["Receive CAD 1,040,000 in one year"]
	    A --> D["Foreign path: convert at spot 1.3500 CAD/USD"]
	    D --> E["Receive USD 740,740.74"]
	    E --> F["Invest USD at 5%"]
	    F --> G["Receive USD 777,777.78 in one year"]
	    G --> H["Sell USD forward at 1.33714 CAD/USD"]
	    H --> I["Receive about CAD 1,040,000 in one year"]
	    C --> J["Covered maturity values match"]
	    I --> J

The domestic path and the foreign covered path end with the same currency on the same date. That common endpoint is essential. Comparing a CAD result today with a USD result next year would not establish parity.

Worked Calculation

Assume:

• spot USD/CAD: 1.3500 CAD per USD;
• one-year CAD rate: 4.00%;
• one-year USD rate: 5.00%; and
• one-year forward USD/CAD: 1.33714 CAD per USD.

Domestic path

CAD 1,000,000 x 1.04 = CAD 1,040,000

Foreign covered path

Convert CAD to USD at spot:

CAD 1,000,000 / 1.3500 = USD 740,740.74

Invest in USD:

USD 740,740.74 x 1.05 = USD 777,777.78

Sell the future USD proceeds forward:

USD 777,777.78 x 1.33714 = approximately CAD 1,040,000

The higher USD interest rate is offset by the lower CAD-per-USD forward rate. An investor does not lock in an extra return merely by moving to the higher-rate currency and covering the exchange risk.

What If the Forward Rate Differs?

Suppose the executable forward were 1.3450 instead of the simplified parity rate of 1.33714. Before costs, the foreign covered path would appear to produce:

USD 777,777.78 x 1.3450 = CAD 1,046,111.11

That exceeds the domestic path by about CAD 6,111. A textbook response would be to borrow CAD, convert to USD, invest USD, and sell the USD proceeds forward.

In practice, this conclusion is incomplete until the analyst uses:

• the CAD borrowing rate, not an unrelated deposit rate;
• the USD lending rate available to that counterparty;
• spot ask and forward bid for the actual trade directions;
• matched value dates and day-count conventions;
• credit, collateral, and balance-sheet charges;
• settlement and operational costs; and
• a size for which every price is executable.

The apparent gain may shrink, disappear, or compensate for risks and constraints omitted from the screen calculation.

CIP and the Cross-Currency Basis

The cross-currency basis is an adjustment showing how the cost of obtaining one currency synthetically through FX swaps or cross-currency swaps differs from direct cash-market funding after accounting for the ordinary rate differential.

Under an idealized CIP relationship, that basis would be near zero. In real markets it can remain nonzero. BIS research documents persistent deviations after the global financial crisis and relates them to factors such as:

• strong one-sided demand for currency hedges;
• limited dealer and arbitrageur balance-sheet capacity;
• funding-liquidity constraints;
• credit and counterparty considerations;
• regulatory and capital costs; and
• transaction and market-liquidity costs.

A nonzero basis therefore carries information about the relative cost of currency funding and hedging. It should not be reduced to “markets are irrational” or “free money is available.”

CIP, FX Forwards, and FX Swaps

CIP can be implemented or observed through related instruments:

The instruments must reference compatible dates and cash flows. A three-month FX forward cannot directly hedge a one-year investment without rollover or maturity mismatch.

Why “Covered” Does Not Mean Risk-Free in Practice

The forward removes uncertainty about the exchange rate applied to the planned foreign-currency maturity amount, assuming the contract performs. Other risks remain:

• the borrower may not obtain funding at the modeled rate;
• the investment or counterparty may default;
• collateral calls may create liquidity pressure;
• spot and forward orders may execute at worse prices;
• settlement of one currency leg may fail;
• the investment amount or maturity may not match the hedge;
• laws, controls, sanctions, or taxes may affect the trade; and
• closing or resizing the structure can be costly.

Covered describes the currency-rate leg, not every economic, legal, or operational risk.

CIP vs. Uncovered Interest Parity

Covered parity uses a contracted forward rate. Uncovered parity uses an expected future spot rate and leaves the currency position open.

See Interest Rate Parity for the umbrella comparison.

How to Test Covered Interest Parity

1. Choose domestic and foreign currencies and state the quote direction.
2. Select a common valuation date and maturity date.
3. Obtain executable domestic borrowing and lending rates.
4. Obtain executable foreign borrowing and lending rates.
5. Use the spot bid or ask required by the initial conversion.
6. Use the forward bid or ask required to hedge the maturity proceeds.
7. Apply consistent day-count and compounding conventions.
8. Calculate both cash-flow paths in the same maturity currency.
9. Deduct transaction, credit, collateral, tax, operational, and balance-sheet costs.
10. Confirm that all legs can be executed at the assumed size and timing.

Common Mistakes

• Comparing midpoint rates instead of executable sides.
• Using the same interest rate for borrowing and lending.
• Reversing the exchange-rate quote without inverting the formula.
• Comparing instruments with different maturities or credit risk.
• Ignoring holidays, value dates, and day counts.
• Calling a forward premium a prediction.
• Calling a gross theoretical basis an arbitrage profit.
• Assuming the forward contract eliminates default and settlement risk.

Risks and Limitations

• Funding risk: Modeled rates may not be available to the participant.
• Execution risk: Prices can move or lack sufficient depth.
• Credit risk: Deposits, securities, and counterparties can differ in risk.
• Collateral risk: Margin terms can change cash requirements.
• Settlement risk: Both currency legs may not settle simultaneously.
• Basis risk: Instruments, dates, or underlying exposures may not match.
• Model risk: Simplified formulas omit discount factors and conventions.
• Legal and policy risk: Controls and enforceability vary across markets.

Related Terms

• Interest Rate Parity: The umbrella framework covering covered and uncovered relationships.
• Interest Rate Differential: The difference between comparable rates in two currencies.
• Forward Points in Currency: The spot-to-forward adjustment visible in FX quotes.
• Currency Hedging: Techniques for offsetting exchange-rate exposure.
• Counterparty Risk: Risk that a party fails to perform its obligation.

Authoritative Sources

• BIS: Covered interest parity lost
• BIS: The failure of covered interest parity
• Federal Reserve: Credit migration and covered interest rate parity

FAQs

Educational Use

This article is for financial education only. It is not investment, trading, tax, legal, or accounting advice and does not recommend a currency, funding trade, hedge, or arbitrage strategy.