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Reverse Conversion

Short stock + long call + short put — an arbitrage play exploiting put-call parity.

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What is a Reverse Conversion?

A reverse conversion (also called a reversal) combines three positions: short 100 shares of stock, long 1 call, and short 1 put — all at the same strike and expiration. By put-call parity, this combination should be equivalent to a short bond (lending money at the risk-free rate), meaning the position should produce a small, predictable profit equal to the difference between the options' fair values and the current risk-free rate. When options are mispriced relative to put-call parity, a reverse conversion can capture that mispricing as a near-risk-free arbitrage. This is a highly technical, institutional strategy used primarily by options market makers and sophisticated arbitrageurs who can execute all three legs simultaneously at tight bid-ask spreads. In modern markets with efficient electronic trading, pricing discrepancies large enough for retail arbitrage are extremely rare.

When to use it

Reverse conversions are not practical strategies for retail traders — the commissions, bid-ask spreads, and borrow costs on the short stock almost always eliminate any theoretical arbitrage profit before the trade is entered. The strategy is included for educational purposes because understanding it deepens your knowledge of put-call parity, options pricing, and how market makers use synthetics to hedge inventory. Professional traders at options market-making firms may execute conversions and reversals to manage their books, adjust delta exposure, or capture small mispricings in illiquid options. For retail traders, the lesson from the reverse conversion is conceptual: it demonstrates why put-call parity is a fundamental constraint on options pricing, and why any apparent "free money" in options markets is almost always an illusion due to execution costs.

Structure

Short 100 shares of the underlying stock, buy 1 call option at the target strike, and sell 1 put option at the same strike and expiration. The short call and long put cancel out the directional exposure, leaving a position that behaves like a synthetic short bond. This requires margin for the short stock position and full cash-securing for the short put, making it capital-intensive.

Key Metrics

Max Profit
A small credit or profit equal to the put-call parity mispricing — typically a few cents per share in favorable conditions. For market makers, this scales across thousands of contracts executed simultaneously with minimal slippage. For retail traders, this theoretical profit is entirely consumed by commissions and bid-ask spreads before the first leg is executed.
Max Loss
Theoretically small if the arbitrage is structured correctly — the position should be near risk-free by construction. However, practical risks include dividend surprises (you owe the dividend on the short stock), early assignment on the short put, or changes in borrow rates that alter the expected profit. In practice, these risks make the reverse conversion non-trivial even for experienced traders.
Breakeven
The position's "breakeven" is the cost of carry — the risk-free rate minus dividends and borrow costs over the options' lifetime. If the combined position generates more than this carrying cost in net premium, it is theoretically profitable. In efficient markets, this gap is nearly always zero for listed options.
Greeks Profile
Near zero on all dimensions — delta, theta, vega, and gamma are all approximately zero because the long stock equivalent (long call + short put) cancels the short stock position. What remains is purely interest rate sensitivity (rho) — a small exposure to changes in the risk-free rate. This near-zero Greek profile is exactly what makes it "arbitrage" — there is almost no market risk remaining in the combined position.

Tips & Best Practices

  • 1This is not a retail trading strategy — it is included to teach put-call parity, which is foundational to understanding all options pricing.
  • 2The conversion (opposite of a reversal: long stock + short call + long put) is more commonly seen when market makers hedge long option inventory.
  • 3Understanding put-call parity prevents overpaying for options by revealing when a position can be replicated more cheaply through a synthetic construction.
  • 4The "box spread" (a conversion and reversal combined) is a related arbitrage that explicitly creates a risk-free position equivalent to a zero-coupon bond.
  • 5If you see an apparent put-call parity arbitrage in a listed stock, check the borrow rate, dividend schedule, and bid-ask spread before assuming there is free money to capture.
  • 6Early exercise risk on American-style options (particularly for deep ITM puts or calls on high-dividend stocks) can disrupt the pricing relationship that makes the reversal work.
  • 7Market makers use conversions to synthetically create short stock without actually borrowing shares — useful when certain stocks are "hard to borrow" at reasonable rates.
  • 8The educational takeaway: if you know the price of a call, the stock price, and the risk-free rate, put-call parity lets you derive the fair price of a put — and vice versa. This relationship governs all options markets.

See it in action

Model a Reverse Conversion with a real ticker. See the P&L chart, heatmap, and exact breakevens.

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