A futures contract usually trades at a different price from the asset it settles against. That spread, the basis, is a readable measure of what leveraged exposure currently costs.
What the basis is
The basis is the gap between a dated futures price and the current spot price, expressed as an annualized rate so contracts of different lengths can be compared.
A future trading above spot is in contango, and one trading below is in backwardation. The words describe the shape rather than any judgment about it.
The gap must close by expiry, because the contract settles against the spot price. That convergence is what makes the spread tradeable rather than merely observable.
Why a positive basis is normal
Holding an asset ties up capital, and someone taking the other side of a long future is effectively financing that position for the duration.
The spread therefore contains an interest component, and in a market where dollars earn a meaningful rate, a modestly positive basis is simply the cost of money.
What traders watch is the excess above that baseline, since it reflects demand for leveraged length beyond what financing costs alone would explain.
The cash and carry trade
A trader can buy spot and sell the future against it, locking in the spread regardless of which way the price moves afterward.
This trade is what keeps the basis anchored, because a wide spread attracts capital until the opportunity narrows to the prevailing cost of funding.
It is not risk free in practice. The position requires margin on both legs, and a sharp move can force additional collateral before the spread has converged.
Perpetual contracts show the same thing faster
Perpetual futures have no expiry and use periodic funding payments between longs and shorts to keep the contract near spot.
Funding is effectively a continuously observable basis, updating several times a day rather than sitting in a term structure that must be interpolated.
Persistently positive funding means longs are paying to maintain exposure, which is a direct statement about which side is crowded at that moment.
How the signal fails
Basis measures positioning, not direction. A crowded long position can persist for a long stretch while prices continue rising, and it can unwind without any price move.
Different venues produce different readings, and the ones with the thinnest books produce the noisiest numbers.
The reliable content is narrow: the basis tells you the current price of leverage and who is paying it, which is useful context rather than a forecast.