How to Calculate Swap Rates

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Written By
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Written By
Dan Buckley
Dan Buckley is an US-based trader, consultant, and part-time writer with a background in macroeconomics and mathematical finance. He trades and writes about a variety of asset classes, including equities, fixed income, commodities, currencies, and interest rates. As a writer, his goal is to explain trading and finance concepts in levels of detail that could appeal to a range of audiences, from novice traders to those with more experienced backgrounds.

Calculating swap rates, especially in the context of interest rate swaps, involves understanding the principles of fixed income and derivatives markets.

Interest rate swaps are financial derivatives that allow two parties to exchange interest rate payments, typically one fixed rate for one floating rate, based on a notional principal amount.


Key Takeaways – How to Calculate Swap Rates

  • Determine the Notional Principal
  • Identify the Fixed and Floating Rate Specifications
    • Fixed Rate
    • Floating Rate
  • Calculate the Payment Periods
  • Calculate Fixed Leg Payments
  • Calculate Floating Leg Payments
  • Netting Off Payments
  • Swap Rate Determination
  • Example Calculations: We give example calculations below.
  • Quantitative Methods: What to do when the calculation isn’t straightforward.


Here’s a deeper outline on how to calculate swap rates for an interest rate swap:

1. Determine the Notional Principal

This is the hypothetical principal amount on which the interest payments will be calculated.

It doesn’t change hands in an interest rate swap but serves as a base for the interest calculations.


2. Identify the Fixed and Floating Rate Specifications

Fixed Rate

This is agreed upon at the inception of the swap and remains constant throughout the life of the swap.

Floating Rate

Typically indexed to a benchmark, like (in previous eras) LIBOR (London Interbank Offered Rate) or SOFR (Secured Overnight Financing Rate), and resets at predetermined intervals.


3. Calculate the Payment Periods

Interest rate swaps have payment periods, often quarterly, semi-annually, or annually.

The frequency of payments will affect the swap rate calculation.


4. Calculate Fixed Leg Payments

Fixed leg payments are calculated by multiplying the notional principal by the fixed rate, then adjusting for the payment frequency.

For example, for a notional principal of $1 million, a fixed rate of 5% annually, and semi-annual payments, the calculation is:


Fixed Leg Payment = $1,000,000 * 5% * 612 = $25,000


5. Calculate Floating Leg Payments

The floating leg payment is recalculated for each period based on the prevailing rate of the underlying benchmark.

It’s calculated similarly to the fixed leg – it adjusts the interest rate according to the current benchmark plus/minus a spread, if any.


Floating Leg Payment = Notional Principal * (Benchmark Rate + Spread) * Payment Frequency


6. Netting Off Payments

The actual cash flow exchanged is often the net difference between the fixed and floating leg payments, depending on the terms agreed upon.


7. Swap Rate Determination

The swap rate is essentially the fixed rate that makes the value of the fixed leg equal to the value of the floating leg at the inception of the swap.

It reflects the market’s expectations of future interest rates and is influenced by factors such as:

  • the yield curve
  • expectations of inflation, and
  • the creditworthiness of the parties

In practice, determining the swap rate involves complex financial modeling and requires solving for the rate that equalizes the present value of the fixed payments to the present value of the expected floating payments.


Financial Modeling Considerations

In real-world applications, calculating swap rates is technical and requires access to current financial data and the use of financial models.

Financial professionals use software and models that incorporate various market factors, including yield curves, spreads, and the credit risk of counterparties.

Due to the complexity and the requirement for real-time data, practitioners typically refer to market quotations provided by financial institutions or use financial modeling software that integrates current values of relevant variables, rather than manually calculating swap rates.


How Do You Read Swap Rates Like “2y5y” and “5y5y”? What Do They Mean?

Swap rates like “2y5y” and “5y5y” refer to forward swap rates.

  • The first number indicates the period until the start of the swap.
  • The second number specifies the length of the swap.

For example, “2y5y” means a swap that will start in 2 years and last for 5 years.

Similarly, “5y5y” denotes a swap beginning in 5 years with a 5-year duration.

These rates are used to gauge future interest rate expectations and are used by traders, investors, and financial professionals planning or hedging interest rate exposure for future periods.


How to Calculate Swap Rates

As an example:

How to calculate 2y5y swap rate based on 2y swap and 5y swap?

To calculate the 2-year forward starting in 5 years (2y5y) swap rate based on the 2-year (2y) swap rate and the 5-year (5y) swap rate, this involves finding a rate that equates the investment returns of two strategies over the same period.


  • R_2_y as the 2-year swap rate
  • R_5_y as the 5-year swap rate
  • R_2_y_5_y as the 2-year forward swap rate starting in 5 years

We need to calculate the R_2_y_5_y, the rate for a swap that starts in 5 years and lasts for 2 years, based on the given rates.

The principle behind the calculation is that the compounded return of investing at the 5-year rate should be equivalent to investing at the 2-year rate for 2 years and then investing at the unknown 2y5y rate for the next 2 years within the 5-year period.

The general approach is:

  1. Convert the swap rates from percentages to decimals.
  2. Use the relationship between the compounded returns of the two strategies to set up an equation.
  3. Solve the equation for R_2_y_5_y

The direct formula to calculate R_2_y_5_y considering the compound interest formula would typically look something like this:


(1+R_5_y)^5 = (1+R_2_y)^2 × (1+R_2_y_5_y)^3


We rearrange it to solve for R_2_y_5_y as follows:


R_2_y_5_y = ((1+R_5_y)^5 / (1+R_2_y)^2)^(1/3) – 1


Let’s do the calculation with hypothetical rates for a 2-year swap rate of 1% (0.01) and a 5-year swap rate of 2% (0.02).

You can use the provided formula to calculate the 2-year forward starting in 5 years (2y5y) swap rate based on a 2-year swap rate and a 5-year swap rate:


R_2_y_5_y = ((1+R_5_y)^5 / (1+R_2_y)^2)^(1/3) – 1



  • R_2_y is the 2-year swap rate (in decimal form)
  • R_5_y is the 5-year swap rate (in decimal form)

You can plug in the specific rates for R_2_y and R_5_y into the formula to get the R_2_y_5_y.

(Be sure the rates are converted to decimal form before performing the calculation.)

Some code:

R_2y = 0.01
R_5y = 0.02

R_2y5y = ((1 + R_5y)**5 / (1 + R_2y)**2)**(1/3) - 1

We get 2.67%.

Let’s try a more challenging example:

5y10y calculation based on a 2y and 30y swap

Calculating the 5-year forward starting in 10 years (5y10y), based on a 2-year (2y) swap rate and a 30-year (30y) swap rate involves a more complex extrapolation because we’re working with non-sequential maturities and the desired forward period doesn’t directly follow from the available rates.

However, we’ll guide you through a general approach to estimate this rate by leveraging the information from the 2-year and 30-year swaps to get an indicative rate for the periods involved.

The formula we’ve been using for forward rate calculation is based on the principle that the investment in a shorter-term rate combined with the forward rate should equate to the investment in a longer-term rate over the same total period.

But without a direct 5y or 10y swap rate, we must infer or estimate the forward rate through alternative means or assumptions.


  • R_2_y as the 2-year swap rate
  • R_30_y as the 30-year swap rate
  • R_5_y_10_y as the desired 5-year forward rate starting in 10 years

We don’t have direct rates for 5y and 10y, which complicates directly computing R_5_y_10_y.

To estimate or approach the calculation, you might consider using interpolation methods to estimate the 5-year and 15-year (since 5y10y is essentially 15 years into the future) swap rates first, based on the 2-year and 30-year rates, then applying the forward rate formula.

But accurately interpolating swap rates requires a curve or a model that reflects how swap rates evolve over different maturities, which might not be straightforward without specific financial modeling software or a detailed yield curve.

An alternative approach is to use market data for 5-year and 15-year rates if available, or to consult financial platforms that might offer calculated forward rates based on current market data.

For educational purposes, if we had the rates for a 5-year swap and a 15-year swap, the formula for calculating the forward rate (Rf) over a period T_1 to T_2 using rates RT_1 and RT_2 is generally expressed as:


(1+RT_2)^T_2 = (1+RT_1)^T_1 × (1+Rf)^(T_2-T_1)


This equation could be rearranged to solve for Rf, the forward rate, if we had the specific rates for T_1 and T_2.

But without direct rates or a clear method to interpolate/extrapolate these rates, providing a specific calculation for 5y10y based on 2y and 30y rates directly isn’t feasible.

For precise calculations, especially in professional or trading contexts, using financial modeling software or platforms that offer yield curve analyses would be necessary.


To estimate a 5y10y swap rate based on 2y and 30y swap rates:

  • Interpolation and Extrapolation – If market data for swap rates closer to the 5y and 15y (since 5y10y is 15 years into the future) points are available, spline interpolation or the Nelson-Siegel model can be used to estimate these rates.
  • Modeling – Using the Vasicek, CIR, or HJM model, one can derive theoretical forward rates, including the 5y10y rate, by fitting the model to the known 2y and 30y rates and any other available market data.

We’ll look a bit deeper at this issue in the following section.

Related: 300+ Quant Interview Q&A


Quantitative Methods for Swap Rate Calculation

Above, we looked at a forward rate such as a 5-year forward starting in 10 years (5y10y) based on a 2-year (2y) and a 30-year (30y) swap rate.

This typically involves using quantitative methods that can interpolate or extrapolate the rates between and beyond the given maturities.

Here are several quantitative methods that could be applied:

1. Linear Interpolation

Linear interpolation is a simple method to estimate rates for maturities not directly quoted but lying between two known values.

While straightforward, it may not always provide the most accurate estimates for longer maturities due to the non-linear nature of interest rate curves.

2. Polynomial or Spline Interpolation

Spline interpolation, including cubic spline interpolation, allows for a smoother and more flexible curve that better fits the term structure of interest rates between known data points.

This method can effectively estimate rates for maturities inside the range of known rates and can be adapted for extrapolation.

3. Nelson-Siegel Model

The Nelson-Siegel model and its extension, the Svensson model, are parametric curve-fitting methods used to describe the entire yield curve with a few parameters.

These models can estimate the entire yield curve from short to long maturities.

They provide a basis for calculating any forward rate.

4. Bootstrapping

Bootstrapping is a method to derive a zero-coupon yield curve from the prices of a set of coupon-bearing products.

From the zero-coupon yield curve, one can derive forward rates.

However, this method requires a broader set of data points than just two swap rates.

5. Vasicek or Cox-Ingersoll-Ross Models

These are one-factor short-rate models used to describe the evolution of interest rates through time.

By fitting these models to market data, one can simulate future paths of short rates and derive forward rates.

These models incorporate assumptions about the volatility and mean reversion of interest rates.

6. Heath-Jarrow-Morton (HJM) Framework

The HJM framework is a multi-factor model of forward rates that directly models the entire forward rate curve instead of just the short rate.

It can incorporate different volatilities for different maturities, so it’s a flexible model for deriving forward rates.


Each method has its strengths and limitations.

The choice of method depends on the:

  • available data
  • specific requirements for accuracy and smoothness of the yield curve, and
  • complexity the users are prepared to manage


FAQs – How to Calculate Swap Rates

What is the first step in calculating swap rates?

The first step is determining the notional principal, which is the hypothetical amount upon which the interest payments of the swap are based.

How are fixed and floating rates defined in the context of interest rate swaps?

The fixed rate is a constant interest rate agreed upon at the start of the swap, which doesn’t change.

The floating rate is typically tied to a benchmark interest rate (like SOFR) and fluctuates over the life of the swap, adjusting at predetermined intervals.

What role do payment periods play in calculating swap rates?

Payment periods determine the frequency of interest payments, which can be quarterly, semi-annually, or annually.

The frequency impacts how interest calculations are performed and thus affects the swap rate calculation.

How do you calculate payments for the fixed leg of an interest rate swap?

Payments for the fixed leg are calculated by multiplying the notional principal by the fixed rate and then adjusting for the payment frequency.

For instance, with a notional principal of $1 million, a 5% fixed rate, and semi-annual payments, the payment would be $25,000 (2.5% * 2) for each period.

How are floating leg payments calculated?

Floating leg payments are recalculated each period based on the prevailing rate of the benchmark index, adjusted for any spread.

The calculation is similar to that of the fixed leg, using the current benchmark rate plus or minus the spread, multiplied by the notional principal and adjusted for the payment frequency.

What is meant by “netting off” payments in the context of swap rates?

Netting off payments refers to the practice of exchanging only the net difference between the fixed and floating leg payments.

Instead of both parties paying each other the full amounts, they only pay the difference, which minimizes the cash flow required.

How is the swap rate determined?

The swap rate is the fixed rate that equates the present value of the fixed leg payments to the present value of the expected floating leg payments at the swap’s inception.

It’s determined through financial modeling.

It reflects market expectations of future interest rates, influenced by the yield curve, inflation expectations, and credit risk.

How are swap rates determined in practice?

Due to the complexity and need for real-time data, professionals use sophisticated financial models and software that integrate current market data.

Calculating swap rates manually is impractical in a real-world setting; thus, market quotations and specialized financial modeling tools are commonly relied upon.

How do you read swap notation?

To understand swap notation, let’s use some examples:

  • “2y5y”
    • “2y” – Indicates the swap will start two years from now.
    • “5y” – Describes the duration of the swap agreement, which lasts for five years.
  • “5y5y”
    • “5y” – Implies the swap’s start five years in the future.
    • “5y” – Indicates a five-year swap agreement.

Give a specific example of why I would want a 2y5y swap?

You might want a 2y5y swap to lock in today’s interest rates for a loan you plan to take in 2 years.

This way you can be sure you have stable interest payments for its 5-year duration and hedge against the risk of increased borrowing costs.

Why are swaps important?

Forward swap rates are important indicators for:

  • Future Interest Rate Expectations – Traders/investors analyze these rates for clues about where they believe interest rates are heading.
  • Hedging Risk – Businesses and financial institutions use forward swaps to hedge their interest rate exposure. For example, locking in a fixed rate for a future period protects them against rising rates.