What Is Basis Risk?
Michael Whitman
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Trading since 2017, full-time since 2020
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YouTube creator, 137K subscribers
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Published 2026-09-14
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Updated
Basis risk is the danger that a hedge and the position it protects stop moving together, leaving an exposure the hedge was supposed to remove. It appears whenever the two instruments differ in maturity, grade, location or venue, which is almost always.
A hedge works by holding something that moves opposite to your position. Basis risk is what happens when “opposite” turns out to mean “mostly opposite, most of the time.”
How it works
The basis is the difference between the two prices. Your holding and your hedge each have a price, and the gap between them is the basis. If that gap were constant, the hedge would be exact.
The gap is not constant. It moves, and every movement in it is a gain or a loss the hedge was not supposed to produce.
Any difference between the two creates it. Different maturity, different grade of the same commodity, different exchange, different currency, different delivery point.
And you almost never get an exact match. The contract that would hedge your position precisely usually does not trade, so you use the nearest one that does.
The trade-off nobody states
A perfect hedge eliminates the risk and the return together. If your hedge moves exactly opposite to your holding, your net position is flat — you have converted an investment into a cash equivalent and paid fees for the privilege.
So nobody actually wants a perfect hedge. What people want is most of the downside removed and some of the upside kept, which requires the hedge to be imperfect on purpose.
Basis risk is therefore not a defect to be engineered away. It is the price of a hedge that leaves anything on the table, and the question is how much of it you are carrying rather than whether you have any.
A worked example
Take a $200,000 stock portfolio hedged with index futures. On a quiet day the holding moves 0.5%, or $1,000, and on a violent day it moves 8%, or $16,000.
Suppose the hedge tracks the holding to within 10% of its movement. On the quiet day the mismatch is about $100 — trivial.
On the violent day it is about $1,600, more than the whole of the quiet day’s move. The same 10% mismatch produced a negligible cost on an ordinary day and a meaningful one on the extreme day.
And the extreme day is when the hedge was needed. Basis risk scales with the size of the move, so it is smallest when it does not matter and largest when it does.
Large moves cluster, so those big mismatches arrive in runs rather than singly — which is how a tolerable basis becomes an intolerable one over a week.
Where it shows up
Commodities. A producer hedging with a futures contract for a different delivery location or a different grade carries basis risk on both differences.
Corporate holdings hedged with an index. The index and the individual company move together approximately, and the approximation is the exposure.
Cross-currency positions. Hedging an asset in one currency with an instrument in another introduces the exchange rate as a third moving part.
And any calendar mismatch. A position held for nine months hedged with a six-month contract leaves three months unhedged and a roll to negotiate in between.
The original data
The S&P 500 shows how large the tail gets. From a close of 1,565.15 on 9 Oct 2007 the index fell 56.8% to 676.53 by 9 Mar 2009, and since 1950 it has had 68 separate stretches of closing 5% or more below its prior record. A hedge that tracked the index to within 10% would have left roughly 5.7 points of that 56.8% fall uncovered — at the one moment protection was the whole point.
That distance between an ordinary pullback and a crisis is what makes basis risk asymmetric. A mismatch expressed as a percentage of the move is small in ordinary conditions and large in the tail, and the tail is the only condition a hedge exists for.
And the hedge costs a round trip of its own — entered and exited, sometimes rolled several times, each one paying the spread and any commission whether or not the protection was ever needed.
The hedge ratio
The amount of hedge per unit of holding is a choice, and it is where basis risk is actually managed. Hedging one-for-one assumes the two move identically; hedging less assumes the hedge moves more than the holding does.
The conventional approach is to size the hedge by measured sensitivity — how much the hedge historically moved for a given move in the holding. That ratio is estimated from past data, which means it carries every weakness of an estimate made over one period.
And the ratio drifts. The relationship that held last year need not hold this year, so a hedge sized once and left alone becomes progressively less matched as conditions change.
Rebalancing it costs money each time. So there is a genuine trade between a hedge that stays accurate and one that stays cheap, and every practical arrangement sits somewhere between the two.
How this connects
A basis swap is the version where the basis itself is the traded instrument. Both legs pay floating rates, and the spread between them is what changes hands rather than a side effect of a hedge.
Convenience yield drives much of the basis in commodities. The benefit of holding the physical good rather than a contract rises when supply is tight, and the gap between spot and futures prices moves with it.
A calendar spread takes this exposure on purpose. Long one maturity and short another, its whole result is the maturity basis a hedger is trying to avoid.
Each approach to expiration forces a decision, and rolling options or futures forward realizes whatever the basis happens to be on the day of the roll.
Currency hedges have their own version. Exchange rate risk is usually hedged in the forward market, and the forward price embeds an interest-rate differential that is itself a basis.
A pairs trading strategy is basis risk turned into the trade itself: long one instrument, short a related one, betting the gap narrows rather than protecting against it widening.
And a hedge fund running offsetting books meets it at scale, because a portfolio that looks market-neutral is often a stack of relationships that can all break at once.
When it fails
The characteristic failure is describing a position as hedged and then sizing it as though it were flat. The hedge removes most of the exposure, the residual looks negligible in normal conditions, and the position is increased on the strength of being protected. Then a large move arrives, the basis widens exactly when the move is biggest, and the residual on a much larger position is larger than the original unhedged exposure would have been. The hedge worked; the sizing decision it enabled did not.
A second failure is measuring the basis in calm conditions. It is stable most of the time, which is precisely why the measurement understates it.
A third is rolling a hedge without pricing the roll. Each roll realizes the current basis and takes on a new one.
A fourth is hedging with a correlated instrument rather than a related one. Correlation measured over a quiet period is not a mechanism, and it breaks under stress.
The question: The hedge lost too. How?
And a fifth is forgetting the hedge has a counterparty. An over-the-counter hedge that performs perfectly is worth nothing if the other side cannot pay, which counterparty risk covers.
Related
Counterparty risk covers the other way a correct hedge fails to pay. Volatility covers the move sizes the mismatch is measured against. And risk management covers sizing a position whose protection is approximate.
Basis risk is what people discover when the hedge they were confident about loses money alongside the thing it was hedging. It is not a failure of the idea — it is the gap between the instrument you wanted and the instrument that exists, and that gap is always there.
— Michael Whitman
This page is educational, not financial advice. Test every idea on your own charts before risking money.