What it means
The Options Industry Council identifies conversion as long stock plus a long put and short call at the same strike and expiration. It calls the opposite position, short stock plus long call and short put, a reverse conversion or reversal.
One conversion typically buys 100 shares and one standard put while writing one standard call, but the option contract's share multiplier must be checked. All three legs should refer to the same underlying and a matched share quantity.
At expiration, if the share price exceeds the strike, the short call can require sale of the shares at the strike. If it falls below, the long put can be exercised to sell shares at the strike.
Ignoring early exercise and settlement details, both outcomes point to the same gross share-sale amount. The put-call parity relationship links stock, put, call, strike, financing and dividends.
An apparent cheap combination may invite a conversion trade, but the quoted spread is not a free cash gift. Carrying stock has a funding cost and may earn dividends.
For example, a stock at $50, a $50 put costing $3 and a $50 call receiving $2 require $51 of net initial cash per share to construct the position before fees. At expiration the option-stock combination delivers about $50 per share, apparently a $1 loss; financing and distributions must be included before judging its economics.
A different quote might produce a positive gross difference, but that is not enough to establish arbitrage. Compare the proceeds to the cost of tying up capital until expiration and the executable bid-ask prices for all three legs.
Borrowing rates, margin requirements, commissions and taxes differ by trader. Market makers may access prices or financing that a retail trader cannot, so a screen showing a theoretical gap is not proof that the user can capture it.
This strategy is generally a relative-pricing and financing trade, not a bet that the share price will rise. The hedge controls much price-direction exposure at expiration but leaves operational and cash-flow risks.
In practice
Real-world examples.
Example
A desk buys 100 shares, buys one put and sells one call at the same $50 strike and expiry. Above $50 the call can take the shares; below $50 the put can allow sale at $50.
Example
A quote screen shows a 20-cent theoretical mismatch per share. The manager finds 12 cents in bid-ask spread and 15 cents in financing cost, so the apparent trade is unattractive.
Example
A short call is assigned shortly before a dividend date. The desk adjusts its stock inventory and checks the realised dividend and settlement cash flows rather than relying on an expiry-only chart.
Formula
Calculation
Ignoring dividends, funding, fees and early exercise, net initial cost per share = stock purchase price + put premium minus call premium. Expiry proceeds approximate the strike price for the matched position, so gross difference = strike minus initial cost. At $50 stock, $3 put, $2 call and $50 strike, cost is $51 and gross difference is negative $1 per share; no arbitrage exists on those simplified figures.
A second case uses a stock at $49.50, a $1.20 put, a $1.00 call and a $50 strike. Cost = $49.50 + $1.20 - $1.00 = $49.70, so gross difference = $50 - $49.70 = $0.30 per share, or $30 on a 100-share position. If financing and fees total $0.38 per share, the net result is $0.30 - $0.38 = negative $0.08 per share, or negative $8 on 100 shares.Case study
Seen in the real world.
Fictional case: An options desk sees a stock at $49.50, a matched $50 put offered at $1.20 and a $50 call bid at $1.00. It calculates a $49.70 initial net debit per share, implying a $0.30 gross difference to the $50 strike before carrying costs. The desk then checks option multipliers, dividend timing, bid-ask depth, margin funding and possible early assignment. Financing and fees total $0.38 per share over the holding period, so it declines the trade.
Its report labels the rejected construction a conversion, not a reverse conversion, and shows every cash flow. The desk keeps the rejected quote in its records as a reference point. If financing costs fall or the quoted gap widens, the same checklist can be rerun in minutes, and the report shows exactly which input would need to change for the trade to clear its costs.
Watch out
Common mistakes.
- Calling short stock with a long call and short put a conversion rather than a reverse conversion.
- Treating a parity gap as risk-free profit without funding, dividends, execution and assignment costs.
- Using mismatched option strikes, expiries or contract multipliers and expecting a locked expiration payoff.
Questions
People also ask.
What are the three legs of a conversion?
Long shares, long put and short call, with matched options and share quantities.
How is it different from reverse conversion?
A reverse conversion shorts the stock and combines a long call with a short put.
Is the return guaranteed if the payoff looks flat?
No. Prices, financing, dividends, transaction costs and assignment mechanics can alter realised results.
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