Who actually lends the shares, and what do they get for it?

Short sellers get the headlines. The lenders — who make the whole thing possible — almost never do. They are, for the most part, the least exciting institutions in finance.

The supply side

• Index funds. The single largest natural source. An index fund holds its list indefinitely and has no plan to sell. Shares sitting still earn nothing; lent shares earn a fee with the fund's price exposure completely unchanged. It is close to free money on an asset the fund was going to hold anyway.
• Pension funds and insurers. Enormous, long-horizon, low-turnover portfolios — the same logic, at scale.
• ETFs. Many lend a portion of their holdings and return some or all of the income to the fund, which offsets part of the expense ratio.
• Sovereign wealth funds and endowments. Same profile again.
• Brokers' own margin customers. Shares held in a margin account in street name are typically lendable under the margin agreement. This is the cheapest borrow of all for a prime broker, because it never leaves the building.

What lending pays

Globally, securities lending revenue to beneficial owners has run on the order of $10 billion a year in recent years. Spread across the world's institutional portfolios that sounds thin, and for a plain-vanilla index fund it is: lending typically contributes a few basis points of annual return.

A worked example makes the scale honest. A $10 billion index fund lends 8% of its assets on average — $800 million — at a blended fee of 30 basis points, and keeps 80% of the revenue after the agent's cut:

$800,000,000 × 0.0030 × 0.80 = $1,920,000 a year

That is 1.9 basis points on the fund's $10 billion of total assets. Modest — but for a fund whose entire expense ratio is 3 to 5 basis points, it covers a meaningful share of the cost of running the thing. Funds that happen to hold names in heavy short demand can earn far more; occasionally a single hard-to-borrow holding generates more revenue than the rest of the portfolio combined.

What the lender gives up

• The vote. Legal title passes to the borrower, and from there to whoever bought the shares. A lent share is a share the fund cannot vote. This is a genuine tension for institutions with stewardship obligations, and many recall shares ahead of contentious meetings — which, seen from the short seller's chair, is recall risk.
• Immediate saleability. Selling a lent security means recalling it first. Usually routine, occasionally not.
• Nothing economic. Price exposure is unchanged; dividends arrive as substitute payments from the borrower; the fee is pure addition.

The part worth remembering

The short seller is not borrowing from an adversary. They are borrowing, almost always, from a passive institution that has no opinion about the stock whatsoever and is simply harvesting a fee on inventory. The lending market is infrastructure, not a battlefield — and the fee is a price for scarcity, not a verdict on the company.

Try it now

1. Open the most recent annual report of two index ETFs from the same family: the iShares Core S&P 500 ETF (IVV) and the iShares Russell 2000 ETF (IWM). iShares publishes both on each fund's page, and they are also filed with the SEC.
2. In each, look for a securities lending income line and the disclosed policy — what percentage of assets may be lent, and how income is split between the fund and the agent.
3. Compare that income to the fund's expense ratio. Only one side of that comparison is in the annual report: the other, each fund's net expense ratio, is in the tables below, the broad fund first and the small-cap one second. It is written as a decimal fraction, so 0.00030 is 0.03%. Ask why the supply-and-demand balance differs between them.