What Is an Interest Rate Swap?
Interest rate swap is an agreement between two parties to exchange interest payments — typically one fixed and one floating — calculated on a notional amount that is never itself exchanged. It converts the character of an existing obligation without replacing the underlying borrowing.
An interest rate swap changes what kind of interest you pay without changing who you borrowed from. It is the most-used derivative in the world and the least visible to anybody outside a treasury department.
How it works
One side pays a fixed rate and receives a floating one. The other does the reverse, and the two streams are netted so only the difference actually moves.
The notional is a calculation base, not a loan. A 100 million swap does not involve anybody handing over 100 million; it means the interest is computed on that figure.
Which is why swap market sizes are misleading. Quoted notionals run into the hundreds of trillions, while the amounts actually at stake are a small fraction of that.
Why not just refinance
Replacing a loan is expensive and slow. Break fees, legal costs, new covenants, and a lender who may not want to lend again on the same terms.
A swap leaves the loan entirely alone. The borrowing, the lender and the covenants are untouched; only the net interest character changes.
And it can be reversed or resized without any conversation with the lender at all, which is the flexibility the instrument is really selling.
A worked example
A company has a 100 million floating-rate loan and wants certainty about its interest cost for five years.
It enters a swap paying 4% fixed and receiving floating on a 100 million notional for five years.
Now trace the cash. The loan costs floating; the swap receives floating and pays 4%. The floating legs cancel, and the company’s net cost is 4% fixed regardless of what rates do.
If rates rise to 6%, the loan costs more and the swap pays more to the company, and the two offset. If rates fall to 2%, the loan costs less and the swap costs the company more — the certainty was bought, and that is what it costs when rates go the other way.
Where the swap rate comes from
It is the fixed rate that makes the two streams equal in value at the start. Neither side pays the other to enter; the rate is set so the swap is worth zero on day one.
That rate is built from expected future short rates, which are themselves read off the money and futures markets rather than forecast by anybody.
So the swap curve is a market-implied path for rates, and it is one of the most closely watched structures in finance because it prices a very large amount of other activity.
But it is not a prediction anybody is making. It is an arbitrage relationship, in the same way a forward price is — and reading the swap curve as a consensus forecast is the same category error as reading a futures curve that way.
The original data
On this site’s thirty-year fee measurement: 5 basis points costs 1.5% of the final balance, 20 costs 5.8%, 75 costs 20.2%, 150 costs 36.5%.
That table is the right scale for thinking about swap pricing. The bid-offer on a vanilla swap is measured in small fractions of a basis point on the fixed rate, and over a long-dated notional those fractions are large absolute amounts — which is why the market is dominated by institutions that can trade at those margins.
And direction runs average 2.01 bars with a longest of 11 on this site’s series — the reminder that a hedge is judged over its full life, not over a stretch where it happened to look clever or foolish.
What actually goes wrong with them
They are marked to market. A swap entered at zero value becomes an asset to one side and a liability to the other as rates move, and that liability appears on a balance sheet even though no cash is owed yet.
Collateral follows the mark. A swap moving against you generates margin calls, so a hedge that is working perfectly in economic terms can consume cash in the meantime.
And the hedge can outlive the exposure. If the underlying loan is repaid early, the swap remains — and what was a hedge becomes an outright position on interest rates that nobody decided to take.
That last one is the failure most worth guarding against, and it is purely administrative. The swap does not know the loan has gone, and nothing tells it.
When it fails
The characteristic failure is a hedge that outlasts what it was hedging. A borrower swaps to fixed, repays or refinances the loan early, and leaves the swap in place — often because unwinding it costs money at that moment. What remains is a naked position on rates, entered by an entity with no view on rates and no mandate to hold one, and it can run for years accumulating gains or losses entirely unconnected to the business. Nothing broke; a relationship between two instruments simply stopped existing and nobody closed the second one.
A second failure is treating notional as exposure. The amount at risk is the replacement value, not the calculation base.
A third is ignoring the collateral demand. A correct hedge still needs funding while it is in profit for the other side.
A fourth is mismatching the floating leg. If the loan and the swap reference different rates, the legs do not cancel and a basis swap exposure is left behind.
And a fifth is judging the hedge by whether rates moved your way. It was bought for certainty, and certainty is worth what it is worth whichever direction the market took.
Related
Basis swap covers the exposure left when two floating rates do not match. Constant maturity swap covers the version referencing a long rate. And clearing house covers where most swaps now sit.
The word notional does a lot of work here and almost nobody explains it. The trillions quoted in swap markets are not amounts anybody owes — they are the number the interest is calculated on, and the real exposure is a small fraction of it.
— Michael Whitman
This page is educational, not financial advice. Test every idea on your own charts before risking money.