Basis (Futures)

The basis was calculated as spot price minus futures price (or futures minus spot, depending on the convention used). In a normally functioning contango market, spot was lower than futures (a negative basis by the spot-minus-futures convention), with the gap representing carrying costs. In a backwardated market, spot was higher than futures (positive basis by the same convention). At expiry, the basis converged to zero as futures contracts settled at the spot price — a process called basis convergence or price discovery.

For Nifty futures on NSE, the basis was derived from short-term interest rates and expected dividends. At any point in time, the theoretical basis for a contract expiring in T days was approximately: Futures Price = Spot × (1 + r × T/365) – PV(dividends), where r was the risk-free rate. When actual futures prices deviated from this theoretical level, arbitrageurs stepped in. If futures were overpriced relative to fair value, cash-futures arbitrageurs bought the spot basket and shorted futures. If futures were underpriced (a condition called discount or negative basis), reverse arbitrageurs sold spot and bought futures.

The basis in individual stock futures carried additional nuances. Near major corporate events — quarterly results, dividend announcements, merger-related news — stock futures frequently deviated from their theoretical fair values as speculators and hedgers pushed prices in different directions. A stock futures contract trading at a significant premium to spot suggested strong bullish sentiment or a squeeze of short sellers, while a persistent discount signalled hedging by institutions or anticipation of a price-weakening event.

Traders who focused on basis trading rather than directional trading sought to profit from mean reversion in the basis. If the basis widened significantly due to an event-driven dislocation and the trader believed it would narrow back to fair value, they would establish a position that profited from this normalisation. This was a form of statistical arbitrage that required precise execution, real-time monitoring, and adequate capital to maintain both legs of the trade simultaneously.

Basis risk was the residual risk that remained even after hedging a spot position with futures. A portfolio manager who hedged an equity portfolio with Nifty futures was protected against broad market moves but still exposed to basis risk — the risk that the portfolio's performance relative to the Nifty index (the tracking error or beta differential) would cause the hedge to be imperfect. Managing basis risk was an important dimension of institutional hedging programs and was distinct from the simpler concept of price risk.