Leverage: borrowing to amplify

Two people buy the same £1,000,000 building. One pays for it entirely with her own money. The other puts in £100,000 of his own and borrows £900,000. The building has a good year and earns £100,000. The first person made 10% on her money. The second made 46% on his — over four times as much, on the exact same building. He looks like a genius. Then the building has a bad year, and the same arrangement that made him a genius wipes him out completely. Nothing about the building changed. Only the borrowing did.

What leverage actually is

Leverage is using borrowed money to control an asset bigger than your own money could buy. You put in a slice; a loan covers the rest; you control the whole thing.

The trick that makes it work — and makes it dangerous — is the fixed claim you met earlier in this course. Debt is a fixed claim. The interest is owed in full whatever the year does. A good year doesn’t make the lender ask for more; a bad year doesn’t let you pay less. The number is set in advance.

That fixedness is the whole story. Once the lender’s slice is fixed, everything above it flows to you. And everything below it eats into you. Your slice is what’s left after the loan is paid — and a leftover, by its nature, swings harder than the thing it’s left over from.

A good year, walked

Take the £1,000,000 building. Interest on borrowing is 6%. “Leverage” is just how much of the purchase the loan covers.

In a good year the building earns 10% — that’s £100,000 of operating profit. Walk three buyers.

No borrowing. You put in the full £1,000,000. You keep all £100,000. That’s 10% on your money — the same as the building earned. No leverage, no magnification.

Half borrowed. You borrow £500,000 and put in £500,000. The loan costs 6% of £500,000 = £30,000 in interest. After paying it: £100,000 − £30,000 = £70,000. But that £70,000 sits on top of only £500,000 of your money. So your return is 14%. The building made 10%; you made 14%.

Ninety percent borrowed. You borrow £900,000 and put in just £100,000. Interest is 6% of £900,000 = £54,000. After paying it: £100,000 − £54,000 = £46,000. And that sits on a tiny £100,000 stake. Your return is 46%.

Same building, same 10% year. Your return climbed 10% → 14% → 46% purely from how much you borrowed. Every pound the building earned above the 6% interest line poured into your shrinking slice, and a small slice magnifies anything poured into it.

The same year, gone bad

Now the building has a thin year and earns only 2% — £20,000. Walk the same three buyers, and watch the magnification run the other way.

No borrowing. £20,000 on your £1,000,000 is 2%. Flat, dull, fine.

Half borrowed. £20,000 of profit, but you still owe the full £30,000 of interest — the fixed claim doesn’t care that the year was thin. £20,000 − £30,000 = −£10,000. On your £500,000, that’s −2%. A building that made money handed you a loss.

Ninety percent borrowed. £20,000 of profit, £54,000 of interest owed regardless. £20,000 − £54,000 = −£34,000, on your £100,000 stake. That’s −34%. The building earned a positive 2% and you lost a third of your money.

Look at the 90% buyer across both years: +46% in the good year, −34% in the bad one. The no-borrowing buyer went +10% then +2%. Same building, but leverage stretched a gentle 8-point spread into an 80-point one. More upside and more downside, in exactly equal measure. Leverage never changed the average outcome of the building. It stretched the spread around it.

The cliff

There’s a floor under the no-borrowing buyer’s losses: the worst the building can do is fall to zero, so the most she can lose is her £1,000,000. The borrower has no such floor.

Say the building doesn’t just earn little — it loses 10% of its value in a crash. That’s −£100,000. The 90% buyer still owes the £54,000 of interest on top. So his slice takes −£100,000 − £54,000 = −£154,000. He put in £100,000. He has lost 154% of his stake — his money is gone, and he still owes £54,000 more than he had.

This is the cliff. When your own money is a thin sliver — 10% here — a fall of just over 10% in the asset doesn’t dent you, it erases you, and then keeps going. You can lose more than everything you put in. The thinner the sliver, the smaller the fall it takes to reach the cliff.

On the whole

This is why the same person is hailed as a visionary in the boom and declared reckless in the bust — often without changing a single decision in between. Leverage is the amplifier sitting underneath the result, and an amplifier makes the quiet parts loud in both directions.

It is not an exotic thing. A mortgage is household leverage: a small deposit controlling a large house, magnifying both the gain when prices rise and the ruin when they fall and the loan still stands. The 2008 crisis was this same mechanism run at enormous scale — slivers of real money under mountains of borrowing, and a fall of a few percent in the underlying assets enough to wipe the slivers out and topple firms that had looked, in the good years, unbeatable. The mechanism is plain once you’ve seen it. The danger is that in the good years it looks exactly like skill.