What is an FX swap, and why is it the most-traded instrument in the world?
Ask a retail trader to name the biggest instrument in the biggest market and you will not hear the right answer. It is the FX swap — bigger than spot, bigger than forwards, bigger than every listed equity derivative. The BIS Triennial Survey has put FX swaps at over 40% of all FX turnover — about $4.0 trillion of a $9.6 trillion day in April 2025, ahead of spot at roughly 30%. Almost no retail participant has ever knowingly traded one, even though every retail position depends on one every night.
The structure
An FX swap is two trades agreed simultaneously with the same counterparty, in opposite directions, on two different value dates:
- Near leg — an exchange today (usually at spot value)
- Far leg — the reverse exchange on a later date, at a rate fixed now
Both rates are agreed at the outset. The far rate is the near rate plus the forward points. That is the entire instrument.
What it actually is
It is not a currency bet. Because the second leg reverses the first, you end up holding the same currency you started with, in the same amount. The exchange rate can do whatever it likes in between and your currency position is unchanged.
What an FX swap is, is collateralised borrowing in one currency against another. You lend one currency and borrow the other for a fixed period, with the currency you handed over serving as the collateral. The price of that borrowing is the forward points.
The worked example
A European company needs USD 10,800,000 for three months. It holds euros. It does not want to sell its euros permanently, and it does not want an unsecured dollar loan.
Using spot 1.0800 and the 3-month forward 1.08537 from the previous lessons:
- Near leg: sells EUR 10,000,000, receives USD 10,800,000
- Far leg (3 months): buys back EUR 10,000,000, pays USD 10,853,700
Cost of the funding: USD 53,700 over three months on USD 10,800,000.
Annualised: 53,700 ÷ 10,800,000 × 4 = 1.99% — which is, to within rounding, the 2.00% gap between the dollar rate and the euro rate.
That is the whole economic story. The company borrowed dollars at the dollar rate, and stopped earning the euro rate on euros it no longer held. The forward points charged it exactly the difference. No view, no forecast, no exchange-rate exposure — a funding transaction with an interest-rate price.
Note also what does not matter: the spot rate used for the near leg. Move it to 1.0900 and the far leg becomes 1.09542 — the points widen to 54.2, because they scale with spot — but the funding rate those points imply is 1.99% either way, identical rather than merely close, because the spot level cancels out of it. The price of an FX swap is the rate the points carry, not the near-leg level they are quoted against.
Who uses it, all day, every day
- Banks funding assets in a currency they do not raise deposits in. A bank with dollar loans and euro deposits closes the gap with FX swaps, rolled continuously.
- Asset managers hedging the currency of a foreign bond or equity portfolio. The hedge is a short forward, rolled every month or quarter — and rolling it is an FX swap.
- Corporates whose receivable slipped: the original forward matures before the money arrives, so the hedge is rolled forward with a swap.
- Retail brokers, every single evening, rolling client positions from one value date to the next. That roll is a tom-next FX swap — the shortest tenor there is — and its points become the "swap charge" on the account. Unit 3 computes it.
When the plumbing strains
Because FX swaps are how the world funds itself in dollars, they are also where a dollar shortage shows up first. The deviation from covered interest parity — the cross-currency basis — sits near zero in calm markets and widens sharply under funding stress, as in 2008 and March 2020. Central bank swap lines exist specifically to relieve that pressure, which is why the phrase is a genuinely significant headline rather than jargon.
One vocabulary distinction to keep straight: an FX swap has two legs and no interim interest payments. A cross-currency swap is the long-dated relative, exchanging principal at both ends and interest in both currencies throughout.
Try it now
- Spot for GBP/USD is in the table of majors below, and a short rate for each currency, SOFR for dollars and SONIA for sterling, under it. Compute the 3-month swap points and the annualised funding cost they imply.
- Redo the calculation with the rates from the first week of September 2024, below, keeping today's spot. The change in the annualised cost is what shifting monetary policy did to the price of funding across currencies.