The mechanics of a vanilla swap
In the most common structure — a "plain vanilla" interest rate swap — Party A pays a fixed rate to Party B, while Party B pays a floating rate (typically SOFR in the US, or SONIA in the UK, replacing the old LIBOR benchmarks) to Party A, on the same notional amount. No principal changes hands. At each settlement date, the net payment flows from the party who owes more to the party who owes less. This netting dramatically reduces counterparty risk compared to exchanging gross amounts.
Why companies use swaps
A company that has issued floating-rate debt (which rises when rates rise) can use a swap to convert its obligation to a fixed rate, locking in its interest cost and removing refinancing risk. Conversely, a company with fixed-rate debt that believes rates will fall might swap to floating. Banks use swaps extensively to manage the duration mismatch between their fixed-rate long-term assets (mortgages) and short-term floating-rate liabilities (deposits).
Valuing a swap
At inception, a fairly priced swap has zero value — the present value of fixed cash flows equals the present value of expected floating cash flows. As time passes and interest rates move, the swap acquires positive value to one party and equal negative value to the other. The swap is valued by comparing the contracted fixed rate against the current market rate for a new swap of the same remaining tenor. If you're paying 3% fixed and new swaps of the same duration trade at 4%, your fixed leg is cheap — your swap has positive value to you.
Credit and collateral risk
OTC (over-the-counter) swaps historically created significant bilateral counterparty risk — if your counterparty defaults when the swap is deeply in-the-money to you, you lose that value. Post-2008 reforms (Dodd-Frank in the US, EMIR in Europe) required most standardised swaps to be centrally cleared through a CCP (central counterparty clearinghouse). Variation margin is exchanged daily so no large bilateral exposures build up. This fundamentally changed the risk profile of the swap market.
"Interest rate swaps are to corporate treasurers what seatbelts are to drivers — not exciting, but essential risk management infrastructure."
What this means for you
Understanding swaps is essential for: corporate treasury (managing debt structure); fixed income investing (swaps define the "swap curve" which prices corporate bonds and mortgages); and rates trading. When central banks move rates, the entire swap curve reprices, affecting billions in corporate debt costs and mortgage rates simultaneously. Swap spreads — the difference between swap rates and equivalent government bond yields — are also closely watched indicators of banking sector stress.