Interest Rate Swap: Fixed for Floating Rate Exchange

Key Takeaways

• An interest rate swap exchanges a fixed periodic payment for a floating one on a notional principal that never changes hands; only the net difference is settled each period.
• IRS notional outstanding reached $469 trillion at mid-2024, making it the single largest segment of the global derivatives market according to ISDA and BIS data.
• A common mistake is thinking the notional is exchanged, unlike a currency swap, a plain vanilla IRS involves no principal transfer at any point.
• A corporate borrower paying SOFR plus 1.50% on a $100 million loan can layer a pay-fixed swap on top, converting the floating obligation to a predictable fixed all-in cost.

What It Is

An IRS has two counterparties and two legs. One party agrees to pay a fixed rate on a notional principal. The other pays a floating rate, reset periodically against a reference benchmark like SOFR. The notional itself is never exchanged. Only the net interest payment changes hands each period.

The size of this market is enormous. According to ISDA's review of BIS data, interest rate swap notional outstanding was $469.2 trillion at mid-year 2024, making up more than 80 percent of all interest rate derivatives globally. Most standardized IRS transactions in the US are now required to clear through a central counterparty under post-Dodd-Frank rules.

The Intuition

Companies and banks borrow at whatever rate the market gives them, but that rate may not be the one they want to carry. A firm that issued floating-rate debt might prefer the certainty of fixed payments. A pension fund holding fixed-rate bonds might want floating exposure to match its liabilities. Rather than redoing the debt, they swap the cash flows.

Think of it as a side contract laid on top of an existing loan. The underlying borrowing stays in place. The swap just converts the economics. If the fixed payer of the swap is also paying floating on a real loan, the net effect is that they now pay fixed overall.

How It Works

At inception the swap is priced so both legs have equal present value, which means the swap is worth zero to either side. That fixed rate is called the swap rate. As market rates move, one leg becomes more valuable than the other and the swap develops a mark-to-market value.

Cash flows are computed on each reset date:

fixed payment = fixed rate * notional * day-count fraction
floating payment = reference rate * notional * day-count fraction
net payment = fixed payment - floating payment

Only the net amount is actually exchanged. Day-count conventions matter. USD fixed legs typically use 30/360, while the floating SOFR leg uses ACT/360. Different conventions produce slightly different dollar amounts even at the same headline rate.

Post-LIBOR, USD swaps reference compounded SOFR. Valuation uses SOFR-based OIS discounting, reflecting the shift to a multi-curve framework after the 2008 crisis.

Worked Example

A corporate borrower has a $100 million floating-rate loan paying SOFR plus 150 basis points. Management dislikes the rate uncertainty and enters a 5-year swap to pay 4.00 percent fixed and receive SOFR on a $100 million notional.

In a quarter where SOFR averages 4.50 percent, the swap flows are:

Fixed leg: 4.00% * $100M * 0.25 = $1.00M paid out. Floating leg received: 4.50% * $100M * 0.25 = $1.125M received. Net on the swap: +$125,000 received.

Meanwhile the loan costs 4.50% + 1.50% = 6.00% * $100M * 0.25 = $1.50M paid.

Combined cash outflow: $1.50M - $0.125M = $1.375M, which equals 5.50 percent annualized, or the original 4.00 percent swap rate plus the 1.50 percent loan spread. The borrower has locked in an all-in fixed cost regardless of where SOFR goes.

Common Mistakes

1. Ignoring day-count conventions. The fixed and floating legs usually use different day-count rules, and the mismatch produces dollar differences that are not obvious from the quoted rates. Always check whether the contract uses 30/360, ACT/360, or ACT/365 before modeling cash flows.

2. Thinking the notional changes hands. The principal in a plain vanilla IRS is never paid. It is only a scaling factor for computing interest. Confusing this with a currency swap, where principal does move, is a frequent error.

3. Assuming the swap eliminates all risk. A swap replaces rate risk with counterparty risk. Central clearing via a CCP greatly reduces that risk for standardized trades, but uncleared bespoke swaps still leave exposure to the dealer. Collateral, margin, and CVA adjustments exist because of this.

4. Confusing an IRS with a rate future. A Eurodollar or SOFR future locks in a single forward rate for one period. An IRS locks in a stream of rates over multiple periods. They are complements, not substitutes, and hedges that mix the two need careful attention to tenor.

5. Forgetting the timing of net payments. Because only net payments move each period, a payer of fixed in a falling rate environment will actually owe money on the swap even though their underlying loan became cheaper. That is the point, but clients surprised by the first margin call did not understand it properly.

Frequently Asked Questions

Q: What is an interest rate swap in simple terms? An interest rate swap is a side agreement between two parties to exchange interest payment streams on the same notional dollar amount, one pays a fixed rate, the other pays a floating rate that resets periodically. No principal changes hands; only the net interest difference is paid each quarter.

Q: How does an interest rate swap affect investment decisions? Swaps let borrowers and investors separate their funding vehicle from their interest-rate preference. A company locked into floating-rate debt that worries about rising rates can pay fixed in a swap, effectively converting its exposure to fixed without renegotiating the original loan.

Q: What is a real-world example of an interest rate swap? A corporate borrower with a $100 million SOFR + 1.50% loan enters a 5-year pay-fixed swap at 4.00%. When SOFR averages 4.50% in a quarter, the loan costs 6.00% but the swap pays a net $125,000 to the borrower, reducing the all-in cost to 5.50%, exactly the 4.00% fixed rate plus the 1.50% loan spread.

Q: How can investors use interest rate swaps in a portfolio? Pension funds with long-dated fixed liabilities use receive-fixed swaps to match duration without selling assets. Asset managers who want to reduce portfolio duration in a rising-rate environment can pay fixed in a swap rather than selling bonds, avoiding transaction costs and potential tax consequences.

Q: How is an interest rate swap different from a rate futures contract? A SOFR or Eurodollar futures contract locks in a single short-term forward rate for one period. An interest rate swap locks in a fixed rate for a stream of payments over multiple periods, months or years. Swaps are the instrument of choice for hedging multi-year rate exposure; futures are better for near-term tactical hedges.

Sources

1. ISDA. "Key Trends in the Size and Composition of OTC Derivatives Markets in the First Half of 2024." https://www.isda.org/a/GpbgE/Key-Trends-in-the-Size-and-Composition-of-OTC-Derivatives-Markets-in-the-First-Half-of-2024.pdf
2. Bank for International Settlements. "OTC Derivatives Statistics at End-December 2023." https://www.bis.org/publ/otc_hy2405.htm
3. CFTC. "Weekly Swaps Report." https://www.cftc.gov/MarketReports/SwapsReports/index.htm
4. CME Group. "Pricing and Hedging USD SOFR Interest Rate Swaps with SOFR Futures." https://www.cmegroup.com/articles/2025/price-and-hedging-usd-sofr-interest-swaps-with-sofr-futures.html

Disclaimer

This article is educational content only and is not financial advice. Nothing here is a recommendation to buy, sell, or hold any security. Consult a licensed advisor before making investment decisions.