Interest Rate Parity Calculator

Interest Rate Parity (IRP) theory states that the difference in interest rates between two countries should equal the differential between their forward exchange rates and spot exchange rates. The calculator utilizes standard day-count conventions (typically 360 days) to convert annual rates into period rates. The price rate and base rate adjustments are computed as: Price Rate = Annualised Price Rate  (Days / 360) and Base = Annualised Base  (Days / 360). From there, the covered forward rate is calculated using the formula: Currency Forward Covered = Spot Price  ((1 + Price Rate) / (1 + Base)), while the uncovered rate uses linear approximation: Currency Forward Uncovered = Spot Price  (1 + (Price Rate - Base)).

Imagine you are analyzing a currency pair with a spot price of 1.2800 GBP/USD. The annualised base interest rate is 4.0% (0.04) and the annualised price rate is 6.0% (0.06). You want to find the 90-day forward exchange rate. First, calculate the 90-day period rates based on a 360-day year: Base = 0.04  (90 / 360) = 0.0100, and Price Rate = 0.06  (90 / 360) = 0.0150. Next, apply the covered forward rate formula: 1.2800  ((1 + 0.0150) / (1 + 0.0100)) = 1.2800  (1.0150 / 1.0100) = 1.28634. Thus, the covered 90-day forward price is approximately 1.2863 GBP/USD.

When applying interest rate parity models, always ensure that your day-count conventions align with market standards (such as Actual/360 for many money market instruments). Keep in mind that real-world transaction costs, liquidity constraints, and capital controls can cause minor deviations from theoretical parity. Utilizing covered interest parity helps lock in guaranteed returns without taking on unhedged foreign exchange risk.