Arbitrage is buying and selling the same asset in two different markets at the same time to pocket a price difference. Buy where it's cheaper, sell where it's dearer, and lock in the gap with (in theory) no view on which way the price goes next.
What does a simple arbitrage look like?
Most Indian stocks trade on both NSE and BSE, and for a moment the two quotes can drift apart. Suppose Sundar Textiles (a fictional company) shows:
| Exchange | Price |
|---|---|
| NSE | ₹250.00 |
| BSE | ₹250.60 |
Divya buys 1,000 shares on NSE at ₹250.00 and simultaneously sells 1,000 on BSE at ₹250.60. Both legs done, she has locked in ₹0.60 × 1,000 = ₹600 (before charges) no matter what the stock does afterwards. Settlement across exchanges is smoother than it used to be thanks to interoperability of clearing corporations. See what is interoperability of exchanges and how does it affect my trading?
The catch: after brokerage, exchange charges, and taxes on both legs, a ₹0.60 gap may shrink to nearly nothing. Arbitrage profits live or die on costs and speed.
What is cash-futures arbitrage?
The same idea works between a stock and its own futures contract. A stock's futures price normally sits a little above its cash (spot) price; that gap is called the basis. Explained in spot price vs futures price and what is basis. If the futures price drifts too far above the cash price, an arbitrageur buys the stock in the cash market and sells the futures against it. Held to expiry, the two prices converge, and the excess gap becomes profit. This "cash and carry" trade is a staple of institutional desks and arbitrage mutual funds.
Why do these gaps close so fast?
Because arbitrage is self-destroying. Every arbitrageur who buys on NSE pushes that price up; every sale on BSE pushes that price down. The trades themselves squeeze the gap shut. With algorithmic traders scanning both exchanges continuously, a visible gap in a liquid stock survives seconds at most, usually less. That is why prices for the same stock on NSE and BSE track each other so closely all day: arbitrage is the invisible thread stitching markets together.
This is also arbitrage's public service. Bystanders get consistent prices everywhere without checking two exchanges; the arbitrageurs collect a sliver of profit for enforcing that consistency.
Can I do this as a retail trader?
You can understand it far more easily than you can profit from it. The gaps that remain in liquid stocks are thinner than retail transaction costs, and the wide gaps sit in illiquid counters where you may not fill both legs at the prices you saw, if one leg fills and the other doesn't, you're not arbitraging any more, you're just holding an open position. One practical footnote: intraday rules generally require squaring off on the exchange where you traded, so a genuine two-exchange arbitrage involves delivery on both legs, with the costs that brings.
Things to keep in mind
- True arbitrage needs both legs done at the seen prices; a missed leg turns a "riskless" trade into an ordinary risky one.
- Charges on two full trades often exceed the gap. Always compute the after-cost profit before admiring a price difference.
- In liquid stocks, algorithms have usually closed the gap before a human can act on it.
- Persistent large gaps in an illiquid stock are usually a warning about liquidity, not free money.
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