Gross Basis

Disambiguation: This page covers gross basis — the raw (pre-carry) spread between a cash bond price and the futures invoice price. It is the starting point before subtracting repo carry. For the carry-adjusted measure used by practitioners, see Net Basis. For futures basis concepts outside the bond market, see Net Futures Basis.

What Is Gross Basis?

The gross basis is the spread between the spot price of a cash bond and the futures price multiplied by the bond's conversion factor. Formally: Gross Basis = Cash Price − (Futures Price × Conversion Factor). It captures the total carry differential between owning the physical bond and holding an equivalent futures position, before netting out financing costs such as repo. The conversion factor normalizes bonds in the deliverable basket to a hypothetical 6% coupon standard set by the exchange, making otherwise incomparable bonds, differing in coupon, maturity, and dollar value of a basis point, directly comparable against a single futures contract price. The bond with the lowest gross basis net of carry becomes the cheapest-to-deliver (CTD), the bond the short futures holder will almost always choose to deliver at expiration because it minimizes their cost. Understanding gross basis at this structural level is essential before engaging with net basis, the delivery option value, or any forward-price analysis of Treasury futures.

Why It Matters for Traders

Gross basis is the raw material of Treasury basis trades, one of the largest and most institutionally significant arbitrage strategies in global fixed income markets. Hedge funds, primary dealers, and relative-value desks systematically monitor basis levels to identify when cash bonds trade cheap or rich relative to futures, constructing long cash/short futures (positive basis) or short cash/long futures (negative basis) positions accordingly. The strategy's appeal lies in its apparent low directionality, in theory, the position converges to zero at futures delivery, but the funding and liquidity risks embedded in the trade are substantial and frequently underestimated.

Beyond pure arbitrage, gross basis functions as a real-time gauge of repo market stress and dealer balance sheet health. When financing costs spike, collateral becomes scarce, or dealers pull back from intermediation, as they did repeatedly post-2008 under Basel III and supplementary leverage ratio (SLR) constraints, the basis can widen dramatically and remain dislocated far longer than models predict. During periods of elevated term premium or acute risk-off sentiment, even small changes in the CTD bond's repo rate can shift the basis by a full point or more, directly affecting the P&L of leveraged basis positions and, in extremis, transmitting stress across the entire Treasury market.

How to Read and Interpret It

A positive gross basis, cash trading above futures × conversion factor, is the structurally normal condition, because bond holders receive coupon income and accrued interest that futures holders do not. Carry is positive for longs in an upward-sloping yield curve environment. In stable markets for 10-year Treasuries, gross basis typically runs between 0.5 and 3 points (where 1 point = 1% of par, or $10 per $1,000 face value), with the exact level driven by the carry component and residual delivery optionality.

When gross basis compresses sharply toward zero or turns negative, it is a warning signal: futures are trading rich relative to cash, often driven by short-squeeze dynamics in the futures contract, forced repo selling, or sudden dealer withdrawal from intermediation. Conversely, an unusually wide gross basis, cash trading far above fair value implied by futures, often reflects a flight-to-quality premium building in specific cash bonds that are held for collateral purposes and are effectively unavailable to deliver.

Traders isolate the net basis (gross basis minus carry) to strip out the predictable carry component and focus on the delivery option value and any residual richness or cheapness. A net basis near zero suggests the market is pricing the delivery option fairly; a consistently positive net basis implies the futures short's delivery options (timing, bond selection, and the wild card option) carry real value that the market is recognizing. Monitoring the spread between gross and net basis over time can reveal shifts in option premium that precede CTD switches.

Historical Context

The most dramatic gross basis disruption in modern history unfolded in March 2020, when the COVID-19 shock triggered simultaneous Treasury selling by foreign central banks liquidating reserves, risk-parity funds deleveraging, and leveraged basis traders facing margin calls. The gross basis on 10-year CTD bonds widened by more than 2.5 points in under two weeks, a multi-standard-deviation move that overwhelmed the risk models of most participants. Basis traders who had entered the trade at roughly 0.5–1.0 points of gross basis suddenly faced catastrophic variation margin as repo markets froze and futures prices fell faster than cash could adjust. Estimated losses across the basis trading community exceeded $10 billion before the Federal Reserve intervened with unlimited Treasury purchases, expanded overnight and term repo operations, and emergency SLR relief.

A more contained but instructive episode occurred in late 2018, when the Fed's quantitative tightening and year-end balance sheet window-dressing by banks caused gross basis on the 5-year CTD to widen by nearly 1.5 points over the December quarter-end period. Repo rates on CTD bonds briefly spiked to special rates well above general collateral, illustrating how collateral scarcity, rather than fundamental mispricing, can dominate gross basis dynamics for weeks at a time.

Limitations and Caveats

The gross basis framework rests on assumptions that can fracture under stress. CTD switches, where a shift in yield level or curve shape makes a different bond the cheapest to deliver, can render an existing basis position immediately uneconomic and in some cases create a loss on both legs simultaneously. The delivery option embedded in futures (the short chooses timing, bond, and in some contracts benefits from the wild card provision tied to end-of-day settlement) creates a premium that is notoriously difficult to price precisely, particularly during volatile rate environments.

Gross basis calculations are also highly sensitive to repo rate inputs. During stress, repo specialness can appear or disappear with little warning, changing the economics of the carry component materially. Regulatory constraints, particularly the SLR, which limits how much leverage dealers can use to intermediate the basis, mean that theoretical arbitrage boundaries are wider in practice than in pre-crisis eras, and dislocations can persist well beyond the horizons most traders can sustain.

What to Watch

• CTD identity and stability: track which bond sits at the bottom of the deliverable basket and model how far yields must move to trigger a switch; CTD transitions accelerate basis volatility
• Repo specialness on the current CTD: a spread between special and general collateral rates of more than 25–50 basis points is an early stress indicator worth monitoring in real time
• Open interest and roll dynamics: during quarterly futures rolls, basis compression or expansion tends to amplify as dealers manage inventory, anomalies here can create short-lived tactical opportunities
• SLR and balance sheet signals: Fed announcements on leverage ratio relief, quarter-end dealer window-dressing, and primary dealer positioning data (published weekly in the Fed's H.4.1 and SIFMA data) all affect the capacity to absorb basis dislocations
• Net basis versus gross basis spread: a widening gap signals rising delivery option premium, often a precursor to increased volatility in the futures contract itself

Gross Basis and the Embedded Delivery Option

The gross basis is not simply a carry number — it also embeds the value of the delivery option held by the short futures position. The short can choose:

• Which bond to deliver (the quality option)
• When during the delivery month to deliver (the timing option)
• Where the bond is held (the location or accrued-interest option, in some markets)

Quantifying the Delivery Option Premium

Gross basis = Net basis + Carry − Delivery option value

Rearranging: Delivery Option Value ≈ Gross Basis − Net Basis − Carry

Or more practically, since Net Basis ≈ Gross Basis − Carry:

Delivery Option Value ≈ −Net Basis

When net basis is positive, the CTD bond's gross carry exceeds its delivery option value — the futures contract is "fair." When net basis is negative, the market is paying for delivery optionality, and the futures price is bid above fair value.

Historical Delivery Option Premiums

Practical rule: When gross basis is unusually wide relative to its historical range for a given yield level, it signals either elevated delivery option premium (normal) or a squeeze developing in the CTD (abnormal). Checking dealer positioning in the repo market helps distinguish the two.