What are margin requirements?

Margin requirements are the rules governing how much of their own capital investors must put up when buying securities on credit. The Federal Reserve's Regulation T sets the initial margin requirement at 50% for most equities, meaning investors can borrow up to half the purchase price from their broker. FINRA's maintenance margin requirement of 25% (and often higher, depending on the broker) specifies the minimum equity that must be maintained in a margin account after the purchase.

When an investor's equity falls below the maintenance margin due to price declines, the broker issues a margin call, demanding that the investor deposit additional funds or sell securities to restore the required equity level. If the investor cannot meet the margin call, the broker liquidates positions at market prices. This forced selling mechanism is what makes margin debt a potential amplifier of market declines: falling prices trigger margin calls, which force selling, which pushes prices lower, triggering more margin calls in a cascading feedback loop.

Different markets have different margin regimes. Futures markets use much lower margin (typically 5-15% of contract value) because the contracts are marked to market daily. Options have complex margin rules based on the strategy employed. Crypto exchanges have historically offered extreme leverage, sometimes 100:1 or more, though regulation has been tightening. Portfolio margin, available to sophisticated investors, allows lower requirements based on the overall risk of the portfolio rather than position-by-position calculations.

Aggregate margin debt levels serve as a sentiment indicator. When margin debt reaches record highs relative to market capitalization, it suggests elevated leverage and speculative activity. Historically, peaks in margin debt relative to GDP have roughly coincided with major market tops, including 2000, 2007, and 2021. However, margin debt also tends to grow during healthy bull markets, making it a confirming rather than leading indicator. The key risk signal is when margin debt declines rapidly, indicating that deleveraging is underway and forced selling may be contributing to price declines.