Securities Lending
Also known as: Stock loan, Sec lending, Securities finance
Renting out shares you already own. The invisible plumbing that makes short selling, market making and settlement work — and quietly earns fund holders a few basis points.
- Asset class
- Money markets (securities finance)
- Instrument type
- Collateralised loan of securities
- Traded
- OTC, agent-lender intermediated
- Typical users
- Index funds, pension funds, custodians, prime brokers
1 · SnapshotThe one idea to remember
2 · BeginnerWhat is it, really?
Securities lending is renting out a share. The lender hands over the stock; the borrower hands back collateral worth more than the stock plus a fee, and returns an identical share later.
Two facts make the whole market comprehensible:
- Legal title actually transfers. The borrower becomes the owner and can sell it — that is the point. The lender gets a contractual right to an identical security back, not the original one.
- Who wants to borrow, and why: short sellers who need something to deliver, market makers covering a sale they have not sourced yet, and anyone facing a settlement fail.
For a large index fund this is not a strategy but a utility: the shares sit there anyway, so lending a slice earns a few basis points that offset the fund's fee. If you own an ETF, you are almost certainly a securities lender without having decided to be.
3 · IntermediateHow it works in practice
How the economics actually flow
- Cash collateral (dominant in the US): the borrower posts cash, the lender reinvests it and pays back a "rebate rate". The lender's income is the spread between reinvestment return and rebate.
- Non-cash collateral (dominant in Europe): the borrower posts government bonds or equities and pays an explicit fee. Simpler, and it removes the reinvestment risk entirely.
- The fee is a price of scarcity: an ordinary large-cap lends at 5–20 bp a year. A crowded short can reach hundreds of basis points, and a genuine squeeze can pass 100% annualised — the borrow rate is a real-time short-interest signal.
What the lender gives up
| Right | What happens |
|---|---|
| Dividends | Paid to the borrower, passed back as a "manufactured payment" — often with a tax difference |
| Voting | Transfers to the borrower; lent stock cannot be voted unless recalled |
| Sale | Retained — the lender recalls the shares, usually within settlement |
The two real risks
Collateral risk: if the borrower fails, the lender keeps the collateral and buys the stock back in the market. The loss is the gap between the two — which is why collateral is marked daily and margined at 102–110%.
Cash reinvestment risk: reaching for yield on cash collateral converts a boring utility into a credit fund. This is precisely what damaged several lending programmes in 2008 — the stock loans performed, the reinvestment portfolios did not.
4 · AdvancedPricing & valuation
The fee as a shadow price
The borrow fee is the market's cleanest measure of short-selling cost, and it enters option arithmetic directly. Put-call parity holds only after adjusting for it — the borrow cost behaves exactly like an extra dividend yield on the underlying:
where \(b\) is the annualised borrow fee. Ignore it on a hard-to-borrow name and the put looks mispriced when it is simply expensive to be short.
Rehypothecation and the collateral chain
- Collateral received can often be reused, and reused again. The resulting collateral velocity multiplies the effective supply of high-quality assets — efficient in calm conditions, and a transmission channel in stress, as margin & collateral sets out.
- Post-2008 rules cap and disclose reuse, and reporting regimes now capture transaction-level data. The market is materially more transparent than it was, without being small: lendable balances run into the tens of trillions.
The governance question for fund holders
Three questions decide whether a lending programme serves the fund or the agent: how is revenue split (60/40 to 90/10 in the fund's favour, and it is negotiable), what indemnity exists against borrower default, and what is the cash collateral invested in. A fund advertising a low headline fee while retaining a large share of lending revenue is not as cheap as it looks — one of the cost layers in costs & fees.
The formulas above are standard textbook formulations, simplified for teaching. They explain the mechanism — they are not a valuation tool, and they will not reproduce a dealer’s price.