Short selling turns the trade sequence around. You borrow shares and sell them, hoping to rebuy cheaper. Then you return them and keep the difference. Losses are uncapped, since a stock can rise without limit, so shorting needs machinery around it. In the US, Reg SHO requires brokers to locate borrowable shares before a short sale, because naked shorting is banned, and a large stock-lending market supplies them. Short interest per stock is published twice monthly via FINRA and the exchanges. India bans naked shorting too. Anyone can short intraday, as long as they square off by the close. But carrying a short overnight means borrowing through the exchange-run SLB (Securities Lending & Borrowing) mechanism, and SLB remains thin. Sustained shorting is therefore structurally harder in India, and analysts argue that's one reason overvaluation can persist longer there.
File one point away for Phase 8. Short sellers are involuntary quality inspectors. When you find a bear report on your company, read it before you read the bull case.
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What are futures and options (F&O)?
Futures & options (F&O) are side bets about prices. A future is a contract to buy or sell later at a fixed price. An option gives you the right to do so without the obligation. They exist for hedging and price discovery. They also enable cheap leverage, and that's where the damage happens. Know three facts now, with the mechanics coming in Phases 7 and 9. (1) India is the world's largest derivatives market by contracts traded. In recent years it has accounted for the substantial majority of global index-option contracts (check the current share in FIA data). (2) SEBI's own studies found that roughly 9 in 10 individual F&O traders lose money. Aggregate retail losses ran to tens of thousands of crores in FY24 alone. Read the studies on sebi.gov.in, since the numbers update. (3) In 2024–25 SEBI tightened the game with one weekly index expiry per exchange, larger minimum contract sizes and higher margins (check the current rulebook).
We'll be blunt about the lesson. F&O is a professional risk-transfer market wearing a lottery-ticket costume. Your edge will come from analysing businesses, and nothing in the derivatives casino changes a company's ROIC. When you do need the mechanics, the material on exchange-traded derivatives covers them. That means contract specifications, lot sizes, expiry and settlement, the margin regime, and how a listed derivative actually clears.
You're probably already wondering something. In a market this well-plumbed, don't prices already contain everything knowable? It's a fair question, and the portfolio-construction material takes it up properly. You'll get the efficient-market hypothesis in its three forms, along with the documented anomalies and what survived out-of-sample. You'll also get our own position on where an individual analyst's edge can come from.
4.9.1 The arithmetic of borrowed money: margin, and the price at which the call comes
Both halves of the material above run on borrowed money. Its arithmetic is short enough to do in your head once you've seen it twice. Two rulebooks set the parameters, and neither one sets the mathematics. In the US, Regulation T fixes initial margin at 50 percent of the purchase. FINRA's Rule 4210 sets a maintenance margin floor of 25 percent on long positions, and most brokers impose a house level of 30 percent or more above it. Both figures are perishable, so verify them against the current Reg T and FINRA rulebooks. In India, buying with borrowed money runs through a broker's SEBI-regulated Margin Trading Facility on an approved list of stocks. Margins are set by the exchange and revises them periodically, and the peak-margin regime from clearing and settlement applies on top (check on sebi.gov.in and the exchange circulars). The worked figures below use 50 percent initial and 30 percent maintenance.
How does buying on margin work?
Start with the position. Buy 500 shares of a ₹1,200 stock and the position is worth ₹6,00,000. Put up 50 percent and your own money is ₹3,00,000. Your broker lends the other ₹3,00,000, and your leverage ratio is 1 ÷ 0.50 = 2.0. Every 1 percent the stock moves is 2 percent of your capital. That ratio is both the appeal and the danger. It's fixed at the moment of purchase, because the loan is a rupee amount that stays put afterwards while the position moves.
Now the return. It has four parts, so count all of them. Sell a year later at ₹1,500 and the position is worth ₹7,50,000. Repay the ₹3,00,000 loan. Pay the interest, ₹3,00,000 × 9% = ₹27,000. Collect the dividends, ₹18 a share on 500 shares = ₹9,000. They're yours, because you own the shares even though the broker financed them. Your ending equity is 7,50,000 − 3,00,000 − 27,000 + 9,000 = ₹4,32,000 on ₹3,00,000 of capital, a return of +44.00%. Unlevered, the same trade returned (1,500 − 1,200 + 18) ÷ 1,200 = +26.50%. Leverage of 2.0 turned 26.50 into 44.00. Why not 53.00? Because of the interest, which you paid whichever way the stock went. Run the stock down to ₹900 instead and ending equity is 4,50,000 − 3,00,000 − 27,000 + 9,000 = ₹1,32,000, a return of −56.00% against the unlevered −23.50%. Losses lever up harder than gains, because the interest counts against you both times.
How do you work out the margin call price?
The number you most need is the price at which the broker calls. Derive it once and you won't need to memorise it. Let P₀ be your purchase price, N the shares, IM the initial margin and MM the maintenance margin. The loan is fixed at P₀ · N · (1 − IM). At any later price P, your equity is P · N − P₀ · N · (1 − IM), and the broker requires that equity to be at least MM of the position value P · N. Divide through by P · N and the share count vanishes. So the call price doesn't depend on how many shares you bought:
(P·N − P₀·N·(1−IM)) / (P·N) ≥ MM
1 − P₀(1−IM)/P ≥ MM
P ≥ P₀ · (1 − IM) / (1 − MM)On these numbers the call price is 1,200 × 0.50 ÷ 0.70 = ₹857.14, a fall of 28.57%. Check it. At ₹857.14 the position is worth ₹4,28,571 and the loan is still ₹3,00,000, so equity is ₹1,28,571, and 1,28,571 ÷ 4,28,571 = 0.30 on the dot. Below that price the broker asks for cash or sells enough of the position to restore the ratio, at whatever price the market is offering that morning.
Worked example: a short sale, with borrow fee and dividend
Shorting reverses every sign. Sell 300 shares short at $80 and the broker holds the $24,000 of proceeds. Add your own 50 percent deposit of $12,000 and the account holds $36,000, against a liability worth whatever the stock is worth. Buy back at $62 and the liability costs $18,600. Two charges belong to the short, and beginners forget both. First comes the stock-borrow fee, here 4 percent for the year on $24,000, or $960. It's charged on the borrowed stock's market value, so a real desk accrues it daily on the current value, and the opening value stops mattering. Second comes the dividend. Whoever bought the shares you sold is now entitled to it, and you must pay it across: $1.10 × 300 = $330. Profit is 24,000 − 18,600 − 960 − 330 = $4,110, or +34.25% on the $12,000 you actually put up. Run the same derivation with a growing liability in place of a shrinking asset, and you get the short's call price as P₀ · (1 + IM) / (1 + MM) = 80 × 1.50 ÷ 1.30 = $92.31, a rise of 15.38%. On identical margins, a short is called after a 15 percent move against it and a long after a 29 percent move. That's the arithmetic behind the old desk saying that shorts have less room than longs.
Two extensions are left for later on purpose. The listed-derivatives material works the futures margin arithmetic. There the exchange sets the initial and maintenance amounts per contract, with no link to a percentage of a purchase. The daily mark-to-market settles the gain or loss in cash instead of letting it accumulate. The governance-and-forensics material works the promoter pledge cascade. That's the same call-price mathematics applied to a controlling shareholder who has borrowed against the company's own stock. In a cascade, the forced sale that restores one lender's cover is what breaks the next lender's.