Whose shares are you selling when you short a stock?

There is a step most explanations skip, and it is the step that makes the whole thing work. You cannot sell what you do not have — not as a matter of ethics, but as a matter of plumbing. Somebody bought those shares from you, and on settlement day they expect delivery.

Settlement is not a formality

Every stock sale has a settlement date: the day the shares and the cash actually change hands. Conventions differ by market — the US and several others moved to one business day after the trade (T+1) in 2024, while the EU, the UK, Switzerland and much of Asia-Pacific still run T+2. Either way, a real transfer has to happen at a real depository, and the buyer's account has to end up holding real shares.

So a short seller has a problem to solve before the order is even accepted: where are the shares coming from?

The answer: a borrow

They come from someone who owns them and is willing to lend them. Your broker locates shares in a lending pool — its own margin customers' holdings, or an external lender's inventory — and strikes a stock loan. Those borrowed shares are what get delivered to the buyer on settlement day.

The buyer, note, has no idea and does not care. They own ordinary shares with ordinary rights, identical to any others. Nothing about their holding is second-class.

Now count the owners

This is the mechanically interesting part. After the trade:

• The original lender no longer holds the shares. They gave up legal title. What they hold instead is a contractual claim to get equivalent shares back, plus collateral, plus a fee.
• The new buyer holds real shares with real votes.

Two parties now have an economic claim on one underlying share. The lender kept the price exposure (they still get one share back eventually) and the buyer has genuine ownership. Nothing was created out of thin air — but the count of claims went up by one.

Follow the chain further and it repeats: the new buyer may hold the shares in a margin account, where they too become lendable, and can be borrowed by a second short seller. This is why the reported short interest in a stock can, and occasionally does, exceed 100% of its free float. It is not a paradox and not evidence of anything improper. It is just re-lending.

What the lender gives up and keeps

• Gives up: legal title, the vote (the borrower's buyer has that), and the ability to sell without recalling the loan first.
• Keeps: full price exposure, and the right to substitute payments — if the company pays a dividend while the shares are on loan, the short seller pays the lender an equivalent amount out of pocket.
• Gains: the borrow fee.

A worked example

Sell 1,000 shares short at $50. You receive $50,000 in cash. Your obligation is not "$50,000" — it is "1,000 shares of this company, plus any dividends they pay while I hold them short, plus a daily fee, returnable on demand". Four separate liabilities, only one of which moves with your opinion of the company.

Try it now

1. Apple's share count is below: the shares outstanding, and the float, which is the shares actually available to trade once large strategic and insider holdings are left out.

2. The table below adds the short interest as a share of the float, written as a decimal fraction. The float is the meaningful denominator rather than shares outstanding, because shares held by insiders and strategic owners are rarely traded or lent. The number of shares sold short is not given, only the percentage, so multiply it back out yourself: short interest × float.

3. Ask the supply question the rest of this course answers: if a large fraction of the float is already sold short, where would the next borrow come from?