Index Fund Machine Ch. 3: Your Fund Lends Your Shares Out

Investment Background

This chapter covers a mechanism almost never explained to retail investors.

Your index fund lends the shares it holds to other people — usually short sellers — for a fee.

This is entirely legal, disclosed, and industry standard. It is also the answer to Chapter 2's "why do some funds slightly beat their index."

And most holders do not know it is happening.

The Wall Street Translation

The Mechanism

Shorting a stock requires first borrowing it.

A short seller's operation: borrow the shares → sell them → wait for the price to fall → buy back → return them.

So where do they borrow from?

From institutions holding large amounts of stock long-term with no intention of selling — that is, index funds.

It is a natural match:

• Index funds hold shares for years without moving them, so lending does not disturb the strategy.
• Short sellers need to borrow temporarily.
• The fund charges a fee, and that fee accrues to fund assets.

So the income ultimately raises your return.

What the Collateral Does

A natural question: what if the borrower does not return them?

That risk is managed with collateral.

The borrower must post collateral — usually cash or high-quality bonds — worth more than the borrowed shares (say 102% to 105%).

And the collateral is marked to market daily: if the share price rises, the borrower must post more.

This is a well-designed mechanism with a good historical default record.

Revenue Split: A Difference Worth Checking

This has a real, comparable consequence.

Lending income does not always accrue entirely to the fund. Many fund companies split it with their lending agent, often an affiliate.

Practice	Where the income goes
All to the fund	100% to you
Split	Part to the fund company

A real difference, and a checkable one — the annual report discloses lending income and its allocation.

This is also a concrete instance of the "costs you cannot see" from Chapter 3 of Where Are the Customers' Yachts?: it is not a fee deducted from your account, it is income that could have been yours and was taken.

Identical effect, entirely different visibility.

Risks: Real But Small

The risks must be listed honestly, not described as zero.

Risk one: the borrower defaults while the collateral simultaneously falls in value.

Collateral covers the normal case. In an extreme case — borrower bankruptcy while collateral assets fall — a shortfall is possible.

Historically this has very rarely materialized, but it is not zero.

Risk two: collateral reinvestment risk.

Cash collateral gets reinvested for yield. If that reinvestment goes wrong, the loss falls on the fund.

This genuinely happened in 2008: some lending programs had reinvested cash collateral in instruments then regarded as safe that later ran into trouble, producing real losses.

That is the mechanism's most notable historical lesson, and its character matches Chapter 2 of When Genius Failed: something regarded as safe proved unsafe under stress.

Risk three: a conceptual objection.

Your fund is helping people short the very stocks you hold.

The economic effect is negligible — short sellers aid price discovery, and your fund is a passive holder. But some investors object on principle, and that is a legitimate preference.

A Necessary Balance

This chapter can trigger an overreaction: "I will avoid every fund that lends securities."

That is nearly impossible in practice and unnecessary.

Almost every large index fund lends securities. Avoiding it entirely means giving up the cheapest, largest, most established products in the category.

And the net effect usually favors you: lending income typically offsets part of the expense ratio, so your real net cost is below the stated fee.

The correct posture: know it is happening, check whether the income accrues to you, and carry on holding.

Consistent with this book's whole attitude — understand the container, do not fear it.

Executable Trading Rules

1. Find securities lending income and its allocation in your core fund's annual report. The chapter's most practical line. You are looking for one thing: how much of that income goes to the fund — which is to say, to you.

2. Understand lending income as an offset to the expense ratio. When comparing two funds, one with a slightly higher stated fee that returns all lending income may cost less in reality. That is why Chapter 2's tracking difference beats the headline fee.

3. Do not abandon broad index funds over securities lending. See the balance above. The net effect is usually positive and avoiding it entirely costs more.

4. Understand this as a concrete form of "costs you cannot see." Customers' Yachts Chapter 3 gave the category; this chapter gives an instance you can actually check.

5. If you object to short selling on principle, that is an actionable preference. A few funds explicitly do not lend, or offer non-lending share classes. A legitimate choice, provided you know its cost (slightly higher net expense).

Relevance to a Retirement Portfolio

This chapter's application for retirees is concrete but limited, and we should size it honestly.

Securities lending will not decide your retirement. Its effect is measured in hundredths of a percentage point per year.

But it is a perfect illustration of this book's core claim:

Your core retirement assets participate in mechanisms nobody told you about. And most of them work in your favor.

The value of knowing them is not switching funds but three things:

One, it explains anomalies. When you see a fund returning slightly more than its index, you now know that is neither magic nor an error.

Two, it lets you compare funds correctly. The headline fee is not the whole cost, and lending income is a common source of the difference.

Three, it is an antidote to the anxiety that "what I hold is opaque." These mechanisms are disclosed, checkable, and comprehensible. Anxiety usually comes from not knowing, rather than from the risk itself.

Consistent with the framework established in Chapter 1 of Against the Gods: what can be named and measured is risk, and risk can be managed. What cannot be named is the problem.

This chapter converts something previously invisible to you into something nameable.

Chapter 4 handles the layer unique to exchange-traded funds: why their price can diverge from their value, and who eliminates that divergence.