The Ten-Percent Margin Trap

Call-Money Loans and Why Paying Down Debt Deepened the Crash of 1929

A retail investor who walked into a Manhattan brokerage office in the summer of 1929 could purchase $100 worth of Radio Corporation of America stock by handing the clerk just $10 in cash. The remaining $90 came from the New York Stock Exchange's call-money desk, where brokers borrowed overnight funds secured by the customer's stock certificates. Call loans could be terminated on twenty-four hours' notice whenever a share price dipped toward the ten-percent equity cushion. Thus, the entire late-1920s bull market rested on a hair-trigger collateral chain. By early October 1929, total broker call loans reached $8.5 billion, exceeding the entire circulating currency of the United States. Over $6.6 billion of that money came not from regulated banks, but from corporate treasurers at companies like Standard Oil and Electric Bond and Share chasing twelve-percent overnight interest rates.

Among the most heavily leveraged buyers was Yale economist Irving Fisher, the preeminent monetary theorist in America. Fisher had also invented the visible-index rotary card file, selling his company to Remington Rand for a fortune exceeding $10 million. Convinced that industrial electrification had placed equities on a permanently high plateau, Fisher borrowed millions on margin to accumulate additional shares right into the autumn of 1929. When prices slipped in mid-October, non-bank corporate lenders suddenly yanked their call money out of Wall Street to protect their own treasuries. Brokers had no choice but to send immediate morning telegrams demanding cash margin from their customers.

On Black Thursday, October 24, and Black Tuesday, October 29, 1929, customers who could not wire cash by 10:00 a.m. had their shares dumped unconditionally at market open. Sixteen million shares changed hands on October 29 as the ticker tape fell two and a half hours behind the floor. Fisher lost his entire $10 million fortune and his New Haven mansion. He had to borrow from his sister-in-law and Yale University just to keep a roof over his head. Searching the wreckage to understand why the economy did not bounce back after the initial liquidation, Fisher published his landmark 1933 Econometrica paper on the debt-deflation theory of great depressions.

Fisher proved that when an entire economy is over-indebted on short-term margin, universal liquidation triggers a mathematical trap. Suppose borrowers start with nominal debt $D_0$ at an initial price level $P_0$. Margin calls then force everyone to dump stocks, commodities, and bank assets simultaneously to pay down a fraction $\alpha$ of their nominal dollar debt. That stampede collapses the velocity of money and drives the general price level down by a fraction $\beta$. The resulting real debt burden $D_{\text{real}}$, measured in purchasing-power units relative to the starting burden $D_0 / P_0$, obeys the ratio:

Whenever distress selling depresses the general price level faster than nominal debts are retired ($\beta > \alpha$), the denominator shrinks faster than the numerator. The real debt burden grows larger than before a single dollar was repaid. As Fisher explained in 1933, the more debtors pay down their nominal balances during a panic, the more they owe in real purchasing power. The collective stampede to liquidate assets defeats each individual's effort to reduce debt. Between October 1929 and March 1933, American borrowers paid off twenty percent of their nominal dollar debts, yet because forced liquidation drove the price level down by forty percent, every remaining dollar of debt weighed thirty-three percent more in real terms.