Covered Interest Parity and Where Forward Points Come From
Every forward exchange rate in the world is built from two interest rates and a spot price. Nothing about it is a view on where the currency is heading.
That single fact explains the swap line on a trading account, the price of a hedge, and one useful piece of evidence a retail trader can borrow from the central banking world.
Key takeaways
- Covered interest parity says the gap between a forward rate and a spot rate must match what the two currencies pay in interest, because otherwise a riskless profit exists.
- Forward points are that gap expressed in price increments. They are an arithmetic output, not an opinion.
- A forward premium is a no-arbitrage price, not a forecast, and reading it as one is the most common error in retail material on this subject.
- The Bank for International Settlements reports that parity stopped holding reliably after the 2008 crisis, with failures carrying on from 2014 onward long after bank funding recovered.
- That residual gap is the cross-currency basis, and the BIS explanation rests on hedging demand meeting real limits to arbitrage rather than on any single crisis.
- The swap charged on a rolled position derives from forward points plus a broker markup, which is why it rarely matches a straight subtraction of one policy rate from another.
Table of contents
- What Covered Interest Parity Actually Claims
- How Forward Points Are Formed From Two Interest Rates
- Why a Forward Rate Is Not a Forecast of the Spot Rate
- What the Cross-Currency Basis Is and Why It Appeared
- How All of This Reaches the Swap Line on Your Account
- Who This Page Is Not For
- Frequently Asked Questions
What Covered Interest Parity Actually Claims
Covered interest parity is a statement about four prices observable at the same instant: a spot exchange rate, a forward rate for some future date, and a money market interest rate in each of the two currencies.
The claim is that these four cannot move independently. Borrowing one currency, converting at spot, lending in the second, and locking the return trip at today’s forward rate produces a fully hedged outcome with no exchange rate exposure left over.
If that sequence returned more than simply lending the first currency at home, the difference would be free money. The word covered refers to that hedge: the return conversion is contracted in advance rather than left open.
So parity is not a theory about behaviour or sentiment. It is an arbitrage boundary.
The relationship runs in a specific direction worth committing to memory. The currency paying more interest trades at a forward discount, and the currency paying less trades at a forward premium. That is the only arrangement under which the interest advantage and the exchange rate movement cancel out.
How Forward Points Are Formed From Two Interest Rates
The forward rate is the spot rate scaled by the ratio of the two interest factors over the period. Forward points are the forward rate minus the spot rate, restated in the increments a quote screen uses.
The figures below are deliberately round illustrative numbers rather than market quotes, chosen so the arithmetic can be followed rather than trusted.
Take a spot rate of 1.1000 on a pair whose base currency carries a three month rate of 2 percent and whose quote currency carries 4 percent. Over a 90 day period the forward rate works out at 1.105473.
Subtracting the spot rate leaves 0.005473, or roughly 55 forward points. The higher rate sits on the quote currency, so the pair trades at a forward premium.
The revealing step is annualising that premium. It comes back to 1.99 percent, the 2 point gap the two currencies started with, less a rounding remainder.
That is the whole mechanism. The forward premium is the interest gap wearing different clothing, converted from a percentage per year into price increments for one settlement date.
Two consequences follow. A longer dated forward carries more points than a short dated one, because the gap accrues over more time. And when two currencies pay the same rate, forward points collapse to roughly zero however volatile the pair is. Volatility never enters the calculation.
Why a Forward Rate Is Not a Forecast of the Spot Rate
A forward quote sits next to a spot quote, dated months ahead, showing a different number. The natural reading is that the market expects the pair to be there on that date. The natural reading is wrong.
Nothing in the derivation above involved an expectation. Four observable prices went in and one came out, bound by the requirement that no riskless profit remains available.
A forward premium of 55 points does not mean anyone expects the pair to rise 55 points. It means the quote currency pays 2 percent more per year, and the premium is what stops that yield advantage being harvested for free.
The distinction has a practical edge. If forwards were forecasts, a persistent discount would be a standing signal to sell the currency. It is not, and treating it as one inverts the relationship.
What a forward does encode is a cost of carry knowable today, useful precisely because it does not depend on anyone being right about the future.
A separate and far weaker relationship, uncovered interest parity, does make a claim about expected future spot rates. Conflating the two is what produces the forecast misreading.
What the Cross-Currency Basis Is and Why It Appeared
Everything above describes a relationship that is supposed to hold. The evidence says it has not.
In its Quarterly Review of September 2016, the Bank for International Settlements published an article whose title states the finding plainly: covered interest parity lost. The authors report a relationship that stopped holding reliably once the 2008 crisis arrived.
The more striking part is not the crisis itself. It is that the failures carried on from 2014 onward, at a point when bank balance sheets had been repaired and funding was readily available again.
The measured gap between the forward rate the market quotes and the rate parity implies is the cross-currency basis. When parity holds that gap is zero. It has not been reliably zero for well over a decade.
The BIS explanation combines two ingredients: persistent demand to hedge dollar exposure forward, and real limits on the arbitrage that would otherwise close the gap.
In BIS Working Paper 590, the same research group puts the second ingredient in commercial terms. Arbitrage consumes balance sheet capacity, so the institutions supplying it charge a premium for taking the other side of hedging demand.
Gaps not explained by dealing costs or bank credit risk are explained by that demand.
The 2016 review also sizes the sensitivity. On the authors’ estimates, when money market stress and forward hedging demand each rise by a percentage point together, the basis widens by something in the order of 45 basis points.
None of this is a historical footnote. The BIS Quarterly Review of December 2025 still cites the 2016 work as the operative explanation, and reports the basis narrowing through the 2022 to 2023 tightening phase as demand for dollar hedges fell away.
| Question | What parity implies | What the BIS documents |
|---|---|---|
| Size of the gap | Zero, beyond dealing costs | A persistent non-zero basis dating from the 2008 crisis |
| Whether it self-corrects | Arbitrage closes it immediately | Failures continued from 2014 onward, after bank funding had recovered |
| What drives any residual | Dealing costs and credit risk | Forward dollar hedging demand meeting arbitrage limits that consume balance sheet capacity |
| Current status | A settled textbook identity | Still the operative explanation in the Quarterly Review of December 2025 |
The practical reading is narrow but real. Parity is the right way to understand where forward points come from, but it is an approximation with a documented error term, not an identity that clears exactly.
How All of This Reaches the Swap Line on Your Account
Holding a spot position past the daily rollover does not settle it. The position is rolled to the next value date, and the price of that roll is a forward calculation over one day.
This is the step most explanations skip, and skipping it produces an avoidable confusion. The swap on an account derives from one day of forward points, not from a straight subtraction of one policy rate from another.
Those two numbers are related but not the same, and several things sit between them. Forward points are formed from tradeable money market rates rather than policy rates, which can diverge considerably.
The cross-currency basis then displaces the result further from the textbook figure. On top of that sits whatever markup the broker applies, and that markup is normally applied to both sides of the pair.
That last point answers a question which puzzles many traders. Parity implies that if one direction of a pair pays, the other should cost, yet plenty of accounts are charged in both directions.
The reason is not that parity has been repealed on that pair. A markup wide enough to cover the side that should receive turns a small credit into a small debit, while the relationship carries on underneath.
Two habits follow. Compare a broker’s quoted swap against the interest gap on the pair, and note the size of the difference rather than its direction alone, because that difference is the cost.
Treat any published swap table as a live commercial figure rather than a constant. It moves with money market rates, with the basis, and with the broker’s own pricing, none of which announce themselves.
This also puts a floor under the carry trade, where the whole proposition rests on the roll being a credit rather than a cost. It matters equally when comparing spot against currency futures and spot forex, where the same carry is embedded in the contract price instead of being charged nightly.
The rates driving all of it are set against a policy backdrop, which is where hawkish and dovish central bank language and the wider machinery of central bank balance sheet policy feed back into the swap line.
Who This Page Is Not For
Anyone who closes every position before the daily rollover can ignore all of it. No roll happens, no swap is charged, and forward points never touch the account.
It is equally of limited use to anyone looking for a directional signal. This explains a cost and a pricing identity, and offers no view on where any currency is going.
Traders whose accounts are structured without overnight interest will find the mechanism largely academic, since the charge is handled through a different arrangement entirely.
It earns its place in three situations: holding positions for days or weeks, comparing brokers on total holding cost rather than spread alone, or working out why a swap does not match the policy rate gap that appears to justify it.
Frequently Asked Questions
What is covered interest rate parity?
It is the condition that the gap between a forward exchange rate and a spot exchange rate must match what the two currencies pay in interest over the same period. If it did not hold, an investor could borrow one currency, convert at spot, lend in the second currency and lock the return trip forward, earning a profit with no exchange rate risk. The word covered refers to that hedge being contracted in advance.
Are forward points a prediction of where the pair will go?
No. Forward points are an arithmetic result derived from a spot rate and two interest rates, and no expectation enters the calculation at any stage. A forward premium exists to stop a yield advantage being harvested for free, not to signal that the pair will rise. A separate and much weaker relationship, uncovered interest parity, does make a claim about expected future spot rates, and confusing the two produces the forecast misreading.
Why does my broker charge me on both sides of the same pair?
Because a markup is normally applied to each direction independently. Parity implies that if one side of a pair pays, the other should cost, but a markup wide enough to cover the receiving side converts a small credit into a small debit. The underlying relationship still holds beneath the pricing; what has been added is a commercial spread around it.
What is the cross-currency basis?
It is the measured gap between the forward rate quoted in the market and the rate covered interest parity implies. When parity holds that gap is zero. The Bank for International Settlements reported in its Quarterly Review of September 2016 that parity stopped holding reliably after the 2008 crisis, with failures continuing from 2014 onward once bank funding had recovered, and its Quarterly Review of December 2025 still cites that work as the operative explanation.
Why is my swap not the difference between the two policy rates?
Because a swap derives from one day of forward points rather than from policy rates directly. Forward points are formed from tradeable money market rates, which can sit some distance from the policy rate; the cross-currency basis moves the result further from the textbook figure; and the broker then applies its own markup. All three effects push away from the simple policy rate comparison.
Sources checked 1 August 2026: Bank for International Settlements, BIS Quarterly Review September 2016, Covered interest parity lost: understanding the cross-currency basis, published 18 September 2016 — for parity ceasing to hold reliably after the 2008 crisis, for failures continuing from 2014 onward once bank funding had recovered, for the framework combining hedging demand with limits to arbitrage, and for the estimate that a one percentage point rise in the Libor to OIS spread together with a one point rise in forward hedging demand corresponds to a basis wider by roughly 45 basis points. Bank for International Settlements, BIS Working Papers no 590, The failure of covered interest parity: FX hedging demand and costly balance sheets, October 2016 and revised November 2018 — for gaps not attributable to dealing costs or bank credit risk being explained by demand to hedge the US dollar forward, and for arbitrageurs charging a premium in forward markets to take the other side of that demand where balance sheet capacity is costly. Bank for International Settlements, BIS Quarterly Review December 2025, Global FX markets when hedging takes centre stage — for the cross-currency basis narrowing during the 2022 to 2023 monetary policy tightening phase as demand for dollar hedges fell, and for that review continuing to cite the 2016 research as the operative explanation. The worked example uses illustrative round numbers for arithmetic clarity and is not a market quotation. No broker swap figure, money market rate or spot rate is stated here as a current market value, because those are per-broker and per-moment.
Disclaimer: This article is educational only, is not investment advice, and is not a recommendation to buy or sell any currency or other instrument. Swap and financing charges are set by each broker, vary by account type and jurisdiction, and change without notice. Trading leveraged foreign exchange and contracts for difference carries a high risk of losing money rapidly.