Implementing a Dollar-Neutral Long–Short Pairs Trade

Summary

The document explains the mechanics of a stock pairs trade: borrow and sell one stock, use the proceeds to buy another, then close both legs when their relative performance meets the strategy’s exit condition. It clarifies that the spread need not return to zero for the trade to profit. The key outcome is whether the long position outperforms the short position on a dollar basis, subject to the chosen hedge ratio.

Real implementation requires capital for margin on the short position, so the trade is not literally costless or free of funding constraints. The hedge ratio also needs to be selected according to the intended neutrality, such as dollar neutrality or market neutrality. The document sketches the trade and its profit condition but does not cover borrow availability, fees, financing details, execution costs, or how to estimate a hedge ratio. Those omissions limit it as a complete implementation guide.

Key ideas

• A basic pairs trade borrows and sells one stock while buying the other.
• Profit depends on the long stock outperforming the short stock on a dollar basis, not necessarily on the spread reaching zero.
• Short-sale margin requirements mean the position still requires capital.
• The hedge ratio should reflect the intended neutrality, such as dollar or market neutrality.
• The explanation omits detailed treatment of borrow costs, availability, and execution expenses.

Tags

# Short sale and zero investmest strategy


# Short sale and zero investmest strategy












Suppose I want to build a pairs trading strategy. Theory says that we can create a zero-investment portfolio by going long stock A and short-selling stock B, given a certain hedge ratio. My question is the implementation of this in the real world.

My intuition:

We borrow stock B by entering a stock reverse repo. We sell stock B in the market at time $t=0$ and with the money from the sale we buy the stock A. When the spread between the A and B is close to zero, we sell the stock A and buy the stock B. We return stock B to the custody plus the repo rate. (For brevity hedge ratio is not taken into account).

Is this correct?

## Answer by AlRacoon (score 3)

https://quant.stackexchange.com/a/43503

You pretty much have this correct. You don’t have to have the spread equal to zero to unwind the trade. All you would care is that the stock you bought (stock A) outperform the stock you shorted (stock B) on a dollar basis in order for this to be a winning trade. In real life you would still need some capital in the trade due to margin requirements on the short position. Also you would need to determine your hedge ratio that should take into account whether you are going to be dollar or market neutral (depending on how you define this neutrality.)

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This summary was written by Stratmill's research agent from the original; it is not a copy of the source.