Interest Rate Parity Calculator

Quickly determine if currencies are in parity using the Interest Rate Parity Calculator. Compute forward rates, premiums, and deviations from spot values to analyze FX arbitrage and investment opportunities.

By CalcMastery Editorial Team

Interest Rate Parity Calculator

Calculate forward exchange rates using Covered Interest Rate Parity (CIP). The formula: Forward Rate = Spot Rate × (1 + Foreign Rate)^T / (1 + Domestic Rate)^T, where T is the time period. Determines if forward rates are at parity or show premium/discount.

Calculate Forward RateVerify Parity

Current exchange rate (units of foreign currency per unit of domestic currency, e.g., EUR/USD = 1.10 means 1 EUR = 1.10 USD).

%

Annual interest rate for domestic currency (typically expressed as percentage per year, e.g., 2.5% for USD).

%

Annual interest rate for foreign currency (e.g., 1.0% for EUR). In IRP, if foreign rate < domestic rate, forward should trade at premium.

years

Custom time period for forward rate calculation in years (e.g., 0.25 for 3 months, 0.0833 for 1 month).

Market forward exchange rate to compare against IRP-implied forward rate.

Results

  • IRP-Implied Forward Rate—
  • Forward Premium/Discount (Absolute)—
  • Forward Premium/Discount (%)— %
  • Parity Status—
  • Deviation from IRP—
  • Deviation (%)— %
  • Interest Rate Differential— %
  • Time Factor— years

Enter your inputs above to calculate the results.

Interest Rate Parity Formula

F = S × ((1 + id)) / ((1 + if))

Where:

  • F = forward exchange rate
  • S = spot exchange rate
  • id = domestic interest rate
  • if = foreign interest rate

    • Forward Premium or Discount

Forward Premium / Discount (%) = (F − S) / S × 100
  • If the result is positive, the currency is at a forward premium.
  • If the result is negative, it’s at a forward discount.

Example

Given:

S = 1.1

,

id = 2.5%

,

if = 1%
F = 1.1 × 1.025 / 1.01 = 1.0839
Forward Discount = (1.0839 − 1.1) / 1.1 × 100 = -1.4634%

So, the domestic currency trades at a 1.46% forward discount.

How to Use the Interest Rate Parity Calculator

Select “Calculate Forward Rate” mode.

This option lets you find the forward exchange rate implied by the spot rate and interest rates.

Enter the following values:

  • Spot Exchange Rate – current exchange rate between the two currencies.
  • Domestic Interest Rate – annual interest rate in your home country.
  • Foreign Interest Rate – annual interest rate in the foreign country.
  • Time Period – choose the time frame (e.g., 1 year).

Get the results

The calculator will compute the IRP-Implied Forward Rate, forward premium or discount, and show if the currency trades at a forward premium or discount.

Review the results.

  • A Forward Discount means the domestic currency is expected to depreciate.
  • A Forward Premium means it’s expected to appreciate.
  • You can also view the interest rate differential and parity deviation if verifying parity.

Frequently Asked Questions

What does the term “Interest Rate Parity (IRP)” mean?

IRP is a financial theory which states that the difference between two countries’ interest rates equals the difference between the forward and spot exchange rates of their currencies.

What does the calculator compute?

It computes the forward exchange rate implied by IRP — i.e., the rate at which currencies should trade in the future given current spot rate and interest rate differential.

Why is the implied forward rate important?

Because if the actual forward rate deviates from the IRP-implied rate, then arbitrage (risk-free profit) may exist — meaning the market may be out of equilibrium.

Can I use this IRP calculator for any currencies?

Yes — as long as you have the correct spot rate and interest rates for the two currencies. But be aware of market constraints: capital controls, transaction costs, and risk may break the ideal IRP relationship in practice.

What limitations should I be aware of when using this calculator?

Key limitations:

  • Assumes free capital mobility and no transaction costs.
  • Assumes perfect substitutability of assets and stable expectations.
  • Doesn’t capture unexpected events, risk premiums, or market frictions that distort actual forward rates.
If the output forward rate is higher than the actual market forward rate, what does that imply?

It suggests that the domestic currency might be expected to depreciate less (or the foreign currency to appreciate more) than market is pricing — which could imply an arbitrage opportunity or extra risk premium is built into the market rate.

Do I need to adjust for compounding frequency or time periods shorter than one year?

Yes. If your interest rates are expressed for a period not equal to the forward horizon in your calculator, you need to convert them consistently (e.g., convert to same basis or period). Many calculators assume a 1-year basis unless noted.

How do I interpret the result from this IRP calculator?

Use it as a theoretical benchmark. If the actual forward rate is close to the calculated rate, markets are roughly in IRP equilibrium. Significant divergence may signal potential arbitrage, risk, or market disequilibrium — but it’s not guarantee of profit (due to real-world frictions).

Is this calculator useful for uncovered interest rate parity scenarios?

Partially — you can use the same structure, but uncovered IRP deals with expected future spot rates rather than hedged forward rates, and it’s much less reliable in practice (many more assumptions).