How Stock Borrow Costs Affect Single-Stock Option Prices

Summary

The document asks how stock borrow rates should enter the pricing of short-dated single-stock options. The proposed approach is to compare European and American option values, then use put-call parity relationships across strikes to estimate funding and borrowing effects. The questioner aims to keep the analysis simple by omitting dividends and more complex volatility assumptions.

The answer claims that higher borrow costs can affect option premiums and may reduce the appeal of positions that require borrowing shares. It does not explain the pricing mechanics in detail or assess the proposed regression approach. In particular, it gives no model, derivation, empirical evidence, or guidance on separating borrow costs from early exercise, dividends, or other inputs. Treat the explanation as an introductory claim rather than a validated calibration method.

Key ideas

• The question proposes using the European-American option price difference to investigate borrowing effects.
• Put-call parity across strikes is suggested as a way to infer financing and borrowing components.
• The answer links higher stock borrow costs to changes in option premiums and trading incentives.
• The document does not validate the proposed estimation method or quantify the effects.

Tags

# How do borrow rates in single-stock options affect their prices


# How do borrow rates in single-stock options affect their prices












Would following approach be suitable:

First calculate European option price (does it even make sense to do so, if we are talking about less than 30 dte?), take the diff between European and American option price, after which you regress on strike against put-call parity and solve for funding, borrowing, etc.

I am ignoring any dividends as I am talking about short-dated SSOs. I want to keep it as simple as possible and not include dividend schedule, stochastic volatilities or the like.

## Answer by Kayla Lee (score -1)

https://quant.stackexchange.com/a/73597

Borrow rates in single-stock options affect their prices in a few different ways. Firstly, when the borrow rate is high, it means that it costs more to borrow the shares needed to sell the option. This increased cost is passed on to the option buyer in the form of a higher premium. Secondly, when the borrow rate is high it also means that the potential for profit is reduced. This is because when the stock price falls, the option will be worth less than the cost of borrowing the shares. As a result, high borrow rates can act as a deterrent to option buyers and lead to lower prices.

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