A calendar spread combines a long position in one futures contract month with a short position in another contract month of the same futures product. A standard calendar spread is typically constructed one-to-one, although non-standard ratio versions can also exist. Its economic exposure is the price relationship between the two expiries: if both months move by roughly the same amount, the spread changes little; if one month strengthens relative to the other, the spread moves even when both futures rise or both fall.
Why the two months do not cancel perfectly
Because the legs share the same product, much of their common outright price exposure offsets, but not all of it. Their relative price changes with the futures term structure. In storable commodities, that relationship can reflect inventory availability, storage and financing costs, seasonality, and delivery-specific constraints; in financial futures, different carry and forward-pricing mechanics may dominate. The spread should therefore not be read as a direct forecast of future spot prices.
Calendar spreads are also central to contract rolls. A trader who is long the expiring contract and wants to remain long can sell the nearby contract while buying a deferred one; a short position is rolled in the opposite direction. When an exchange lists the calendar spread as a single strategy order, the two legs can be executed together, avoiding the temporary outright exposure created by manually entering one leg before the other. Reduced directional exposure does not mean zero risk. Margin systems may recognize offsets between expiries, but the position retains basis risk because different contract months are not perfectly correlated.
The sign depends on the convention
A practical trap is assuming that “buying the spread” has a universal leg direction. It does not. Exchanges can use buy-near/sell-deferred conventions for some products and sell-near/buy-deferred conventions for others; the displayed spread can likewise be calculated as near minus deferred or deferred minus near. Across markets, a month-pair label alone is therefore not a universal statement of economic direction. This matters in charting and backtesting because the same relative relationship represented with the opposite subtraction convention produces a sign-inverted series. Before comparing spread histories, define the contract months, the long and short legs, any leg ratio, and the exact subtraction convention.