Syntethic short vs short position for a hard to borrow stock

External question — Quantitative Finance Stack Exchange Author: phdstudent Original post: https://quant.stackexchange.com/questions/85724 License: CC BY-SA 4.0 — https://creativecommons.org/licenses/by-sa/4.0/ Adaptation: HTML converted to plain text; contact email addresses removed. I am sure this is trivial for short sellers, but what am I missing with this synthetic short. But an example below with actual quotes as of Jul-21st-2026. If I short 100 shares of CVNA at $63.77, I pay ~$ 0.48/day in borrow = ~$264 over 18 months. (robinhood quote) Is there a cleaner way to get the same short exposure? Instead of shorting the stock, I go long the 64 put + short the 64 call (Jan '28 expiry) (schwab quote with correct ask for long put and bid for short call) Same −100 delta. But I get a $348 CREDIT up front instead of bleeding borrow every day. The options are pricing in ~0% borrow while my broker charges me ~2.75%/yr. Net result: the synthetic beats the outright short by ~$625/contract, roughly constant at any expiry price. If CVNA is flat at expiry: outright short LOSES ~\$254 to borrow. Synthetic MAKES ~$371. That's ~6.6%/yr of carry edge on a hard-to-borrow name. The catch: my short 64 call is American. If borrow spikes, it gets assigned early and I'm back to paying $0.48/day. But I can always close this an it's an unlikely event. So is that ~6.6%/yr just fair payment for assignment risk... or free money? What am I missing?

External answer — Quantitative Finance Stack Exchange Author: Jordan Boekel Original post: https://quant.stackexchange.com/a/85760 License: CC BY-SA 4.0 — https://creativecommons.org/licenses/by-sa/4.0/ Adaptation: HTML converted to plain text; contact email addresses removed. When you short a stock, you get cash upfront. Most retail brokers do not credit you the interest for this, or if they do they credit it at a lower rate. If you do this via options, the market maker you trade with faces no such limitations. They short at institutional rates and collect the cost of carry, so if the prevailing risk free rate is 4% the options will be priced with an implied interest rates equivalent to this. Add your possibly excessive borrow fee (CVNA doesn't look that expensive to borrow to me) and you get your 6.6% carry difference.

External answer — Quantitative Finance Stack Exchange Author: user93883 Original post: https://quant.stackexchange.com/a/85782 License: CC BY-SA 4.0 — https://creativecommons.org/licenses/by-sa/4.0/ Adaptation: HTML converted to plain text; contact email addresses removed. When you short a stock, the borrow rate is not fixed and can change from day to day. You can also be bought in—your position can be forcibly closed by the broker if the shares are recalled. When you create a synthetic short with American options, the embedded/implied borrow cost will in general differ from your broker’s overnight borrow cost. The main risks are early assignment on the short call, failure to early-exercise the long put when optimal, and pin risk at expiry. In Vola Dynamics Library implied borrow is automatically calculated on every snapshot market snapshot, so you can see the value for each expiry and how it changes over time.