Margin debt is the money investors have borrowed from their brokers to buy stocks, and this card shows how fast that borrowing is growing compared with a year earlier. Fast growth means investors are piling on leverage. Growth ran into the 50-80% range before the 1973, 2000, 2007 and 2022 bear markets.
It is not a sell signal on its own. The same surges happen early in recoveries, as in 1983, 2003 and 2009-10, when investors start borrowing again after a crash. So read it together with where the economy is in its cycle: a surge late in a long bull market is a warning sign, while a surge coming out of a bear market usually is not. The rating ranks the latest growth rate against every month since 1960, with faster growth rated as higher risk.
From 1997 the data is FINRA's monthly total of debit balances in customers' securities margin accounts. Before 1997 it covers NYSE member firms only, scaled so the two series join without a jump. FINRA publishes each month's figure around the third week of the following month.