Borrow Costs And Short Selling Fees

To sell a stock short, you have to borrow the shares first — you don't own them, so someone else's shares are lent to you, sold into the market, and you owe those shares back later. That loan isn't free. The lender charges a borrow fee, quoted as an annualized percentage of the position's value, and for most large-cap stocks it's negligible. But for a subset of names — small caps, stocks with heavy short interest, stocks in the middle of a well-publicized short squeeze — the fee can run into the double digits annually, sometimes even over 100%, turning the cost of simply holding the position into a bigger risk than the price move you're betting on.

Why the fee varies so much

Borrow fees are set by supply and demand in the securities lending market, not by the exchange. A stock with abundant lendable shares — held in size by index funds and institutions willing to lend them out for a small fee — trades "general collateral" (GC), with a borrow rate near zero. A stock where many funds want to short it but few shares are available to borrow becomes "hard to borrow" (HTB), and the fee rises to ration the scarce supply, sometimes daily, as demand shifts. In the extreme, a stock can go "no borrow" entirely, meaning new short positions simply cannot be opened at any price because no lendable shares exist.

Worked example

A fund wants to short $1,000,000 of a small-cap stock that's trading at a 15% annualized borrow fee — high but not extreme. Held for three months, the borrow cost alone is roughly $1{,}000{,}000 \times 0.15 \times 0.25 = 37{,}500$, i.e. $37,500, before any commission or the stock even moving. If the thesis is that the stock falls 10% over that quarter, the fee eats nearly 40% of the expected gross profit on the trade. Now compare a large-cap stock at a 0.3% annualized fee: the same three-month hold costs $1{,}000{,}000 \times 0.003 \times 0.25 = 750$, i.e. $750 — over 50 times cheaper for the identical dollar exposure and holding period, purely because of borrow availability.

What this means in practice

A short seller has to underwrite the borrow cost alongside the price thesis, and check it isn't static: fees can spike mid-position if a stock suddenly becomes crowded (many funds piling into the same short) or if lenders recall shares, forcing the short to be bought back ("buy-in") at an inopportune moment regardless of the trader's own view. This recall risk is a structural feature of short selling that a long position never faces. Quantitative strategies that screen for short candidates typically filter out or heavily discount names with high or rapidly rising borrow fees, since a great thesis on a 50%-fee stock can still lose money if the price doesn't fall fast enough to outrun the accruing cost.