Conversion Arbitrage Strategy in Indian Markets: A Worked Example

What Conversion Arbitrage Actually Is

A conversion is a precise options structure, not a vague cash versus futures trade. You build three legs at once on the same underlying, strike and expiry: go long the underlying in the required quantity, buy one at the money put, and sell one at the money call. The long put plus short call together behave like a short futures position, called a synthetic short. So you own the stock and are synthetically short the same stock at a fixed strike. The position is fully hedged: whatever the stock does, you exit at the strike.

Because direction is neutralised, your result depends only on the price you paid to build the package, and profit is locked the moment you enter. It equals the strike, minus the stock price, plus the net premium collected, minus cost of carry and all charges. If the call you sell is fatter than the put you buy by more than it costs to hold the stock to expiry, the package prints a small fixed profit. That gap is the arbitrage.

This is the definition many shallow guides get wrong. Conversion arbitrage is not simply buying cash and shorting a future and waiting for them to converge. That is cash and carry, a related but different trade. A true conversion uses options to build the short leg, which is why put and call premiums, not just the futures basis, drive the edge.

Why the Mispricing Appears: Put Call Parity and Cost of Carry

The trade exists because of put call parity, which ties a call, a put and the underlying together. When the call gets bid up or the put gets cheap, the synthetic short trades above the real stock price, and a conversion captures that difference. It happens when call demand is heavy, when short selling the cash stock is hard, or when borrowing costs and dividends are mispriced into the options.

Your cost of carry is the money you tie up to hold the stock until expiry. Buy shares worth several lakh for 25 days and you lose the interest that capital could have earned, or you pay margin funding interest. The conversion only works if the options gap more than covers carry plus charges. Any dividend before expiry is a bonus to you as holder, and the options usually price it in, so check the ex dividend calendar.

A Fully Worked Example on Reliance

Let us run a concrete, illustrative example on Reliance Industries, a liquid NSE stock with active options. The F&O lot size for Reliance is 500 shares. Assume a monthly expiry 25 calendar days away. These numbers show the method, not a live quote, so always check the real chain before trading.

• Reliance cash price: 1,300 per share. You buy 500 shares, so capital used is 6,50,000 rupees.
• Chosen strike: 1,300 (at the money), same monthly expiry for both options.
• You SELL the 1,300 call and receive a premium of 32 per share.
• You BUY the 1,300 put and pay a premium of 20 per share.
• Net premium collected: 32 minus 20 equals 12 per share, that is 12 times 500 equals 6,000 rupees received.

At expiry your stock effectively exits at the 1,300 strike no matter where Reliance closes. Above 1,300 the call you sold is exercised; below 1,300 you exercise your put. Either way the exit is fixed at 1,300, so the stock leg is flat and your gross gain is the 6,000 rupees of net premium collected up front.

Now subtract cost of carry. You parked 6,50,000 rupees for 25 days. At 9 percent a year, that interest is 6,50,000 times 0.09 times 25 divided by 365, about 4,007 rupees. So before charges the position is 6,000 collected minus 4,007 carry, roughly 1,993 rupees of gross edge, and we have not paid a single charge yet. The raw gap looks attractive, but the carry eats most of it.

The Full Cost Stack: Brokerage, STT and Statutory Charges

Indian charges are where most paper conversions die. You have several charged legs: buy stock, sell stock at expiry, sell the call, buy the put, and settle both options. Below are realistic charges with a discount broker charging a flat 20 rupees per executed order.

The single biggest line is STT on the cash legs. Buying and selling 6.5 lakh of stock as delivery attracts 0.1 percent each side, 650 plus 650 equals 1,300 rupees, before anything else. Add brokerage, exchange charges, GST, SEBI fee and stamp duty and the round trip total lands near 1,750 rupees.

Net result, illustrative: gross premium 6,000, minus carry 4,007, minus charges about 1,750, equals roughly 243 rupees of net profit on 6,50,000 of capital tied up for 25 days. That is about 0.037 percent for the period, under half a percent annualised, so thin that a single rupee of slippage on any leg flips it to a loss. That is the honest reality of conversion arbitrage for a retail trader in India.

Lot Size and Why Indices Do Not Fit a Pure Conversion

A true conversion needs you to hold the underlying in the exact quantity the options control. For Reliance, one contract covers 500 shares, so you buy 500 shares to match one call and one put. For an index it breaks down, because you cannot buy the Nifty or Bank Nifty index itself in the cash market. Nifty options control 65 units, Bank Nifty 30, FinNifty 60 and Sensex 20, but there is no single cash instrument to hold against them.

• Nifty lot size 65 and Bank Nifty 30: no direct cash holding, so a textbook conversion is not possible on the index itself.
• FinNifty lot size 60 and Sensex 10: both index only, same limitation.
• Single stocks such as Reliance (500), HDFC Bank, TCS or Infosys have a real cash share you can buy in the lot quantity, so they are the practical candidates.
• Anyone claiming index conversions usually means a futures based or ETF based basis trade, a different structure with different risks.

Stock options in India are also American style, so the short call can be exercised early, especially around a dividend. Your stock then gets called away before expiry and the hedge breaks at an awkward moment. This early exercise risk is an often ignored reason conversions on single stocks are trickier than the textbook suggests.

Entry and Execution Rules That Actually Matter

Compute the locked profit before you place any order: strike, minus stock price, plus call premium, minus put premium, all times lot size, then subtract carry and your full charge estimate. Proceed only if that number is clearly positive. Execution must be near simultaneous, because if the call premium drops before you sell it your edge is gone, and most retail platforms lack a true single click conversion.

• Pick one liquid stock with tight option spreads and the strike nearest to spot.
• Quote all three legs together, never leg in slowly, the gap closes in seconds.
• Compute locked profit per share, multiply by lot size, subtract carry and charges.
• Confirm no dividend ex date that could trigger early call assignment, or price it in.
• Check you have margin for the short call and the cash for the shares before sending orders.

Exit Rules and Settlement Mechanics

The cleanest exit is to hold to expiry. The options settle, the stock converts at the strike, and the profit you locked at entry lands without timing anything. The catch is that in the money options go to physical settlement, the rule for Indian stock derivatives, so you need shares ready for the short call and must be prepared to receive shares on the put. Single stock options are monthly, so your time frame is the monthly cycle, not weekly index expiries.

Risk, Margin and What Can Still Go Wrong

On paper a conversion is market neutral and low risk, but the practical risks are real, and the biggest is margin: even fully hedged, you must fund the entire stock purchase and post margin on the short call, so capital efficiency is poor against the tiny return. Watch for these specific failure points.

• Early exercise of the short call around dividends, breaking the hedge before expiry.
• Slippage on any of the three legs turning a positive trade negative.
• Physical delivery obligations at expiry and short delivery penalties if shares are not in your demat.
• Liquidity gaps in the put or call, forcing a bad fill.
• Underestimating the full charge stack, especially STT on both cash legs.

Journal every leg, the premium captured, the carry assumed and the actual charges debited, then compare to your pre trade estimate. After honest accounting, most retail traders find conversion arbitrage on Indian single stocks is a thin, capital heavy trade that suits only those with low cost execution and patience.

How Conversion Compares to Related Strategies

It helps to place conversion next to its cousins. Cash and carry shorts a future, not options. A box spread uses four options and no stock, so it has no delivery risk. A reversal is the exact opposite of a conversion, used when the synthetic is cheap rather than rich.

Taxation of Conversion Arbitrage in India

This is critical and frequently misunderstood. Profits from F&O trading are treated as business income, not capital gains, and taxed at your slab rate. The options legs fall squarely under business income. So the 243 rupees of net profit in our example, and any larger conversion profit, is added to your business income and taxed at your slab, up to 30 percent plus surcharge and cess.

The cash equity leg is more nuanced. Treated as investment, equity held one year or less is short term capital gain taxed at 20 percent, and equity held longer is long term capital gain taxed at 12.5 percent on gains above 1.25 lakh a year. Because conversions usually run only to the next monthly expiry, you are almost always in the short term or business income bucket. Keep clean records and consult a chartered accountant for your situation.

Sources and Further Reading

For authoritative contract specifications, charges and rules, refer to NSE India, SEBI, Zerodha Varsity and the Income Tax Department. Always confirm the current lot size, STT rate, margin and settlement rules on the official source before you trade. All numbers in this guide are illustrative and educational, and nothing here is a promise of profit.

Sources and Further Reading

For authoritative data and further reading on this topic, refer to NSE India, SEBI (Securities and Exchange Board of India), Zerodha Varsity and Income Tax Department. Always confirm current rules, rates and contract specifications on the official source before you trade.