Interest Rate Swap Definition: An interest rate swap is a contract in which one party pays a fixed interest rate and the other pays a floating rate, both calculated on the same notional amount in the same currency. Only the net difference changes hands on each payment date, so a borrower can turn a floating-rate loan into a fixed-rate one without refinancing. The swap gains value for the fixed-rate payer when market rates rise and loses value when they fall.
What Is an Interest Rate Swap?
Most loans charge either a fixed rate that never changes or a floating rate that resets every few months. Borrowers do not always hold the kind they want. A company with a floating-rate bank loan may lose sleep over rising rates, while a bank with fixed-rate mortgages on its books may worry about the opposite.
An interest rate swap lets each of them change the shape of their payments without touching the original loan. It is the most common kind of swap, and by notional value the largest derivative market in the world. The standard version, called a plain vanilla swap, has one fixed leg and one floating leg.
The floating leg follows a benchmark interest rate. For decades that benchmark was LIBOR, a rate built from bank submissions. After banks were fined for manipulating it, regulators replaced it, and new US dollar swaps now reference SOFR, a rate based on actual overnight lending backed by Treasury securities.
How Does an Interest Rate Swap Work?
Once the concept is clear, the mechanics come down to three numbers: the notional, the fixed rate and the floating rate on each reset date. The fixed rate is set so that the swap is worth zero on day one, meaning it equals what the market expects the floating rate to average over the swap’s life. From then on, every change in expectations moves the swap’s value.
Consider a company with a $50 million, five-year loan at SOFR plus 1.5%. To remove the rate risk, it enters a swap: it pays a fixed 4% on $50 million and receives SOFR. The SOFR it receives cancels the SOFR it pays the bank, so its all-in cost becomes 4% plus 1.5%, or a fixed 5.5% ($2.75 million a year).
Now test it. If SOFR rises to 5%, the loan costs 6.5%, or $3.25 million, but the swap pays the company the 1% gap between 5% and 4%, which is $500,000. Total cost: $2.75 million. If SOFR falls to 2%, the loan costs only $1.75 million, but the company pays $1 million on the swap, and the total is again $2.75 million.
The company gives up the chance to benefit from falling rates in exchange for certainty. That trade is the core of hedging with swaps.
Traders measure swap risk in basis points through a number called DV01, the dollar value of a one-basis-point move. For a $50 million five-year swap, DV01 is roughly $22,500: every 0.01% change in five-year rates moves the swap’s value by about that much.
Interest Rate Swap vs. Bond
Receiving fixed in a swap behaves much like owning a fixed-rate bond funded with floating-rate borrowing. Both gain when rates fall. What they need up front is very different.
| Receive-Fixed Swap | Fixed-Rate Bond | |
|---|---|---|
| Cash needed at start | Only collateral or margin | Full purchase price |
| Principal at risk | None, the notional is never paid | Full principal if the issuer defaults |
| Main exposure | Interest rate moves | Rate moves plus issuer credit risk |
| Income | Fixed rate minus floating rate | Coupon payments |
| Leverage | High, since exposure far exceeds cash posted | None unless bought with borrowed money |
This is why pension funds and insurers use swaps to match long-dated liabilities. They get the rate exposure of a long bond while keeping their cash invested elsewhere.
Why Are Interest Rate Swaps Important for Traders?
Swap rates at each maturity form a swap curve, a close cousin of the government yield curve. When a central bank surprises the market, two-year swap rates often move first, because they price the expected path of policy rates over that window. Traders read the gap between two-year and ten-year swap rates the same way they read the slope of Treasury yields.
The biggest risk is not the swap formula but the collateral behind it. Cleared swaps are marked to market every day, and the losing side must post cash. That leverage turned into a crisis in the UK in September 2022: after the government’s mini-budget on 23 September, 30-year gilt yields jumped by more than a percentage point in days.
British pension funds that used swaps and borrowed gilts to hedge their liabilities faced sudden margin calls. To raise cash, they sold gilts, which pushed yields higher and triggered more calls. On 28 September the Bank of England stepped in with up to £65 billion of gilt purchases to stop the spiral, even though the hedges had worked on paper.
Key Takeaways
- An interest rate swap exchanges fixed payments for floating payments on the same notional, and only the net difference is paid on each date.
- Borrowers use swaps to turn floating-rate debt into fixed-rate debt, giving up the benefit of falling rates in exchange for predictable costs.
- The fixed rate is set so the swap starts at zero value, so later moves in rate expectations create gains for one side and losses for the other.
- Receiving fixed in a swap resembles owning a bond with borrowed money: similar rate exposure, no principal paid, and far more leverage.
- Daily collateral calls are the practical risk, because a hedge that is correct on paper can still force selling when it needs cash.
Who pays whom in an interest rate swap?
On each payment date the two amounts are compared and only the difference is paid. If the floating rate is above the fixed rate, the fixed-rate payer receives the gap; if it is below, the fixed-rate payer pays it.
What replaced LIBOR in interest rate swaps?
In the US, new swaps reference SOFR, the Secured Overnight Financing Rate, which the New York Fed has published since April 2018. The main US dollar LIBOR settings stopped after 30 June 2023, and older contracts moved to SOFR-based fallbacks.
Can an interest rate swap lose money even if it is a hedge?
Yes, the swap itself can show a loss, but for a true hedge that loss is offset by a gain on the loan or bond it protects. The real danger is the cash needed for collateral calls while the swap is under water, which can arrive before the offsetting gain turns into cash.
What is a swap spread?
A swap spread is the gap between a swap's fixed rate and the yield on a government bond of the same maturity. It reflects bank credit risk, supply and demand for bonds, and balance-sheet costs, and it can even turn negative.
