Reversal
Arbitrage

What is a reversal?

A reversal — also called a reverse conversion — is an arbitrage built from three legs at one strike price: you go short the underlying, sell a put option and buy a call option. The short put and long call together form a synthetic long that exactly offsets the short stock, so the position's value at expiry stops depending on direction. What remains is a fixed, locked outcome — pure arbitrage rather than a market bet.

Like its mirror image, the reversal lives off put-call parity. When the market prices the put too richly relative to the call and the cost of carrying a short position, a reversal captures that gap as a small, near-certain profit. It is the trade desks reach for when the put, rather than the call, is the leg that is temporarily overpriced.

Key takeaways

• A reversal is an arbitrage, not a view — the payoff is flat at every settlement price.
• Construction is short underlying + short put + long call, all at the same strike and expiry.
• The short put and long call form a synthetic long that cancels the short stock.
• Profit comes from put-call-parity mispricing when the put is relatively overpriced.
• The real risks are borrow cost, dividends, early assignment and slippage — not the market.

How a reversal works

Assemble all three legs at the same strike K. Being short the stock means you gain as price falls; the short put caps that gain below K, while the long call protects you above K. Below K the put you sold is exercised against you and you buy back at K; above K you exercise your call and buy at K. Either way you end up buying at K to cover, so the terminal value is fixed and the only variable is the net credit you took in versus the strike.

In Indian markets the practical hurdles are real. Shorting cash stock requires a borrow — with a borrow fee and recall risk — while index reversals use futures instead. Selling the put blocks SPAN + exposure margin, and STT, brokerage and the bid-ask spread all erode the edge. Theta and implied volatility do not move the locked payoff because the option legs hedge each other — but they do create the entry mispricing. NIFTY options are cash settled; many single stocks settle by physical delivery, which changes the unwind mechanics.

The numbers that matter

Worked NIFTY example

Suppose NIFTY is near 22,500 and you spot the put trading rich at the 22,500 strike. You short NIFTY exposure at 22,500, sell the 22,500 put for ₹190 and buy the 22,500 call for ₹150. Your effective sell level plus net premium works out to about 22,540, while every leg resolves at the 22,500 strike. With a lot size of 75, the locked profit is roughly (22,540 − 22,500) × 75 = ₹3,000 before costs (illustrative figures):

NIFTY at expiry	Outcome	P&L (1 lot)
21,500	Put assigned, buy back at 22,500	+₹3,000
22,500 (strike)	Both options expire near zero	+₹3,000
23,000	Call exercised, buy at 22,500	+₹3,000
24,000	Call exercised, buy at 22,500	+₹3,000

The P&L column is flat — exactly as in a conversion, only assembled from the short side. The single question for a reversal is whether that ₹3,000 survives the borrow fee, costs and any dividend adjustment.

When to use a reversal

• You see a put trading rich relative to the call and carrying cost at the same strike.
• You can borrow the stock cheaply (or use futures) without recall risk.
• You can execute all three legs together to avoid leg-in slippage.
• You run a professional or market-making book set up to monetise tiny, repeatable edges.

Risks to respect

• Borrow cost & recall: the stock you are short can become expensive to borrow or be recalled, breaking the structure.
• Dividends: as the short stock holder you owe the dividend, which can erase the locked edge.
• Early assignment: an in-the-money short put can be assigned before expiry, unbalancing the hedge.
• Execution slippage: the edge is so thin that a poor fill on any one leg can wipe out the trade.

Reversal vs conversion

The conversion is the exact mirror of the reversal: long stock, long put and short call. A conversion is the play when the call is relatively expensive; a reversal is the play when the put is relatively expensive. Both lock a flat payoff from put-call parity, just from opposite sides of the underlying. Desks run whichever direction the temporary mispricing favours, often holding offsetting books in both.

Reversal vs box spread

A box spread reaches the same locked, near risk-free return but uses four option legs across two strikes and never touches the underlying. The reversal needs an actual short position — with its borrow fee, recall risk and dividend liability — whereas the box is purely option-based. Both are effectively interest-rate arbitrages, and both succeed only when the captured edge clears all transaction costs.

Common adjustments

If the short put goes deep in the money or a dividend looms, traders often roll or close the position early to dodge assignment and the dividend liability. Many desks also unwind the whole package the instant the parity gap closes rather than carrying it to expiry — banking the edge quickly and recycling the margin into the next dislocation.

Frequently asked questions

What is a reversal in options trading?

A reversal, or reverse conversion, is short stock combined with a short put and long call at the same strike. The option legs form a synthetic long that offsets the short stock, locking a flat, near risk-free payoff.

How does a reversal differ from a conversion?

It is the mirror. A conversion is long stock plus long put and short call and exploits a rich call; a reversal is short stock plus short put and long call and exploits a rich put.

Is a reversal really risk-free?

It is near risk-free at expiry — the synthetic long hedges the short stock. The real risks are borrow cost and recall, dividends, early assignment of the short put and execution slippage.

Why are reversals rare on NSE?

Liquid markets keep options close to parity, so the edge is tiny and usually consumed by STT, brokerage, borrow cost and margin. They surface mainly in illiquid strikes or around dividend and expiry dislocations.

The bottom line

The reversal is the short-side twin of the conversion: a short underlying locked against a synthetic long, leaving a flat payoff whose only variable is whether the captured put-call-parity edge clears borrow, dividends and costs. It is a pricing-error harvest, not a directional trade. For Indian retail the edges are usually too thin and the borrow too awkward to bother, so reversals stay on professional desks — but they are essential to grasp if you want to understand how synthetic positions and arbitrage really work.

Related strategies & terms

• Conversion — the mirror image that exploits a relatively rich call.
• Synthetic Long — the short-put-plus-long-call core that hedges the short stock.
• Box Spread — the same locked return using four option legs, no stock.
• Assignment · SPAN Margin · Expiry