What is arbitrage trading?

Arbitrage rests on a simple principle: the same asset should cost the same everywhere at the same moment. When it briefly does not — because of a lag, a temporary order imbalance, or a structural link — an arbitrageur buys the cheaper version and sells the dearer one simultaneously, locking in the difference regardless of which way the market then moves.

Crucially, both legs are executed together. That is what separates arbitrage from a directional trade: you are not predicting whether the price rises or falls, only that the gap between two prices for the same thing will close. When it works, the profit is the spread minus costs.

Cash-futures arbitrage. A stock’s futures price is linked to its cash price by a cost-of-carry relationship. When the futures trade richer or cheaper than that fair value, a trader can buy one leg and sell the other, capturing the mispricing as the two converge by expiry.

Cross-exchange arbitrage. The same share listed on both NSE and BSE can momentarily quote different prices. Buying on the cheaper exchange and selling on the dearer one captures the gap — if it survives transaction costs and the order actually fills on both sides.

Index arbitrage. The price of an index future and the basket of its underlying stocks should stay aligned. When they drift apart, large players trade the future against the basket to pull them back together.

Pure arbitrage is competitive precisely because it looks low-risk. Many participants watch the same gaps, so they close in fractions of a second, and the remaining spread is usually thin. After brokerage, exchange charges, taxes and the bid-ask spread on both legs, an apparent gap can vanish entirely.

This is why genuine arbitrage tends to be the domain of well-capitalised, automated participants who trade large volumes at very low per-trade cost. For most individuals, the gaps that survive costs are rare, and chasing them manually means the price has usually moved before both legs are filled.

Arbitrage is often called risk-free, but that is only true if both legs execute together at the expected prices. Execution risk — one leg fills and the other does not — leaves you with an unhedged, directional position. Liquidity risk means you may not be able to exit one side cleanly. And costs that look small can swamp a thin spread.

There is also the risk that the gap was not a true mispricing at all but reflected something real — a halted stock, a corporate action, or stale data. Treating every price difference as free money ignores why the difference exists. The discipline is to act only when the gap is genuine and the costs are covered.

Ordinary trading takes a view on direction: you buy because you expect the price to rise. Arbitrage takes no view on direction — it profits from two prices converging, whichever way the overall market moves. That makes its return profile different: many small, quick gains rather than a few large directional ones.

Because the edge per trade is so small, arbitrage depends on volume, speed and cost control rather than on being right about the market. It is a useful concept to understand because it explains why prices across NSE, BSE and the derivatives market stay broadly consistent — arbitrageurs constantly close the gaps that appear.