Pairs Trading in Indian Markets: A Worked HDFC and ICICI Example

What Pairs Trading Actually Means

Pairs trading is a market-neutral strategy. You buy one stock and short-sell another stock that historically moves with it, sizing the two legs so the position has very little net exposure to the overall market. If the Nifty falls 2 percent, both your long and your short tend to fall together, so the loss on one side is largely offset by the gain on the other. What you are really trading is the spread between the two stocks, not the direction of the market.

The bet is simple to state. Two related companies usually trade in a stable relationship to each other. Sometimes that relationship stretches because of a news flow, a block deal, index rebalancing or plain noise. Pairs trading assumes the stretch is temporary and that the two prices will revert toward their normal relationship. You go long the one that has become relatively cheap and short the one that has become relatively expensive, then wait for the gap to close.

Because you hold a long and a short at the same time, your profit does not depend on guessing whether the market goes up or down. It depends on convergence, the spread returning to normal. That is why the strategy is grouped with statistical arbitrage and spread trading rather than with directional trend following.

The HDFC Bank and ICICI Bank Pair

HDFC Bank and ICICI Bank are the two most liquid private banks on the NSE. They share the same regulator (RBI), the same broad loan book mix and the same interest-rate sensitivity, so their prices tend to move together over time. That shared driver is exactly what a pairs trader wants: a relationship strong enough to revert, but with enough day-to-day noise to create entry points.

The core tool is the price ratio: HDFC Bank price divided by ICICI Bank price. Suppose over the last six months HDFC averaged around Rs 1,650 and ICICI around Rs 1,100, giving an average ratio close to 1.50. You do not trade the ratio at 1.50; you wait for it to move far from 1.50 and then fade the move. To judge how far is far, traders convert the ratio into a z-score: how many standard deviations the current ratio sits from its mean. A common rule is to enter when the z-score reaches plus or minus 2, and exit when it returns toward 0.

A Fully Worked HDFC and ICICI Trade (Illustrative)

Here is a complete, numbers-first example. Treat every figure as illustrative, not a forecast. Assume the six-month mean ratio is 1.50 with a standard deviation that puts a ratio of 1.42 at roughly a minus 2 z-score. On the entry day the prices are: HDFC Bank Rs 1,562 and ICICI Bank Rs 1,100. The ratio is 1562 divided by 1100, which is 1.42. HDFC has become relatively cheap versus ICICI, so the trade is: long HDFC Bank, short ICICI Bank.

We size the two legs to be roughly rupee-balanced so the position is close to market neutral. Long leg: buy 100 HDFC Bank at Rs 1,562, which is Rs 1,56,200 of exposure. Short leg: sell 140 ICICI Bank at Rs 1,100, which is Rs 1,54,000 of exposure. The two notionals are within about 1.4 percent of each other, which is close enough for a retail pair. The short leg is taken in the futures segment or as an intraday short, because in the Indian cash market you cannot carry a naked short overnight.

Now the spread converges. Over the next few sessions the ratio climbs back from 1.42 toward its 1.50 mean. Say it reaches 1.50 with HDFC at Rs 1,650 and ICICI at Rs 1,100 (1650 divided by 1100 is exactly 1.50). You close both legs. The long leg gains (1650 minus 1562) times 100, which is Rs 8,800. The short leg: ICICI did not move, so that leg is flat at Rs 0. In this clean case the convergence came entirely from HDFC catching up, and your gross profit is about Rs 8,800.

In a more typical convergence both legs move. Suppose instead the ratio returns to 1.50 because HDFC rises to Rs 1,624 (up Rs 62) and ICICI falls to Rs 1,082 (down Rs 18). Long leg: Rs 62 times 100, which is Rs 6,200 profit. Short leg: you sold at Rs 1,100 and buy back at Rs 1,082, gaining Rs 18 times 140, which is Rs 2,520. Combined gross profit is about Rs 8,720, and crucially it held up even though both stocks moved, because the spread is what you were really trading. If you scale the same trade to roughly Rs 3 lakh per leg, the gross profit scales to roughly Rs 18,000.

Counting the Real Costs: STT, Brokerage and Taxes

Thin spreads make costs decisive. Pairs trading involves four trade legs in total (buy and sell on the long stock, sell and buy on the short stock), so transaction costs hit you twice as hard as a single-stock trade. The table below shows the main charges on the Rs 1.56 lakh long HDFC leg, assuming an intraday equity trade with a discount broker. The short ICICI leg carries similar charges.

Across all four legs of the HDFC and ICICI pair, round-trip costs typically run into a few hundred rupees on a roughly Rs 3 lakh-per-leg trade. On our Rs 18,000 gross example that is small, but on a trade that only captures Rs 1,500 to Rs 2,000 of convergence, costs can quietly swallow a third or more of the edge. That is why pairs traders favour highly liquid names like HDFC and ICICI: tight bid-ask spreads keep slippage low, which matters more than the headline brokerage.

On taxes, intraday equity legs are speculative business income and short F&O hedges are non-speculative business income; both are taxed at your income-tax slab rate, not at the flat capital-gains rates. If instead you hold the long leg as a delivery position for a few days and book it, the gain is a short-term capital gain taxed at 20 percent (plus cess). Long-term capital gains (holding over one year) are taxed at 12.5 percent above Rs 1.25 lakh of gains in a financial year, but pairs trades are rarely held that long. Always confirm your own classification with a tax professional.

How to Hold the Short Leg in India

India has a specific constraint: you cannot short a stock in the cash market and carry it overnight. A cash-market short must be squared off the same day. This matters because most pairs trades need a few days for the spread to converge, not a few hours. There are two practical ways around it.

• Use stock futures for the short leg. HDFC Bank, ICICI Bank and many large caps have liquid single-stock futures. You can hold a short future for the life of the contract, rolling at expiry. Lot sizes vary by stock and are revised periodically by the exchange, so check the current contract specification before sizing.
• Use index proxies. Because banking pairs are rate-sensitive, some traders express one leg through Bank Nifty futures (lot size 30) or Bank Nifty options, though this changes the pair from stock-vs-stock to stock-vs-index and adds basis risk.
• Keep both legs intraday. If your model fires and converges within the session, you can run both legs in the cash market and avoid the futures route entirely. This is cheaper on margin but limits you to fast-converging signals.

If you use futures, remember that margins apply to both legs. Even though the position is market-neutral in spirit, the exchange does not automatically net your long stock against your short future across segments, so plan for the combined margin. Some brokers and the exchange offer margin benefits on recognised hedged positions, but never assume it; check before you commit capital.

Finding and Validating a Pair

A good pair has an economic reason to move together, not just a coincidental chart shape. Same-sector leaders are the natural starting point: HDFC Bank and ICICI Bank in private banking, TCS and Infosys in IT services, or Reliance versus a sector index. The economic link (same demand drivers, same regulator, same input costs) is what gives you confidence the spread will revert rather than drift apart forever.

Validation is a two-step statistical job. First, measure correlation of daily returns over a meaningful window (six to twelve months) to confirm the two move together. Second, and more importantly, run a cointegration test on the price spread to confirm the spread itself is stationary and mean-reverting. Correlation alone is a trap: two stocks can be 0.9 correlated and still have a spread that wanders off and never comes back. Cointegration is the property that actually makes the convergence bet sound.

Entry, Exit and Stop Rules

A pairs trade needs all three rules defined before you enter, because once you are in two positions at once it is easy to freeze. A workable template using the z-score of the HDFC-to-ICICI ratio: enter when the z-score reaches minus 2 (long HDFC, short ICICI) or plus 2 (short HDFC, long ICICI); take profit when the z-score returns to roughly 0, meaning the ratio is back near its 1.50 mean; and place a hard stop if the z-score pushes beyond 3, because that is the market telling you the relationship may have broken.

• Entry: z-score at or beyond plus or minus 2. Long the relatively cheap leg, short the relatively expensive leg.
• Profit target: z-score back to roughly 0 (spread reverted to mean). Book both legs together.
• Stop loss: z-score beyond plus or minus 3, or a fixed rupee loss on the combined position, whichever comes first.
• Time stop: if the spread has not converged within a set number of sessions (say 10 to 15), exit. A trade that refuses to revert is a warning, not a discount.
• Event guard: stand aside around results, RBI policy, and index rebalancing dates that can shock one leg without the other.

Common Mistakes That Cost Indian Traders Money

The most expensive mistake is assuming correlation is permanent. The HDFC and ICICI relationship has shifted across cycles, and the HDFC Bank and HDFC Ltd merger in 2023 is a reminder that corporate actions can permanently change a stock's behaviour. A pair that worked beautifully last year can quietly stop reverting, and a trader who keeps adding to a losing spread on the belief that it must converge can lose far more than the small edge the strategy normally targets.

The second mistake is ignoring costs and the short-leg constraint. Because every pairs trade has four legs, plus STT on every sell, plus GST and stamp duty, the break-even move is larger than beginners expect. Add the fact that the short leg usually has to be a future (with its own margin and roll cost), and a strategy that looks like free money on a backtest can bleed in live trading. The third mistake is over-leveraging: market-neutral does not mean risk-free, and a leveraged spread that diverges can produce a margin call on both legs at the same time.

Risk Management and SEBI Rules

Pairs trading is legal and unremarkable from a regulatory standpoint, but you still operate inside SEBI and exchange rules. Short selling in the cash segment must be disclosed and squared intraday; carrying a short overnight is done through the F&O segment, which has its own margin, position-limit and expiry mechanics. Equity F&O contracts in India are cash-settled or physically settled depending on the instrument, and single-stock futures are physically settled at expiry, so you must close or roll before the contract expires to avoid delivery obligations.

For risk control, size each pair small relative to capital, cap the number of simultaneous pairs so a sector-wide shock cannot hit all of them at once, and keep a written stop on every trade. Maintain a trading journal that records the entry z-score, the ratio, both leg prices, costs and the exit, so you can tell whether your edge is real or just survivorship bias. Discipline, not prediction, is what keeps a market-neutral book alive.

Sources and Further Reading

For authoritative data and current contract specifications, lot sizes and charges, refer to NSE India, Zerodha Varsity and SEBI. Pairs trading shares ideas with statistical arbitrage and depends on stable correlation. Always confirm current rules, tax rates, STT and contract specifications on the official source before you trade. All figures here are illustrative and not a promise of returns.

Sources and Further Reading

For authoritative data and further reading on this topic, refer to NSE India, Zerodha Varsity and Investopedia. Always confirm current rules, rates and contract specifications on the official source before you trade.