Margin is the collateral a broker requires to open and maintain a leveraged position.

Margin is the collateral a broker requires to open and maintain a leveraged position. Leverage lets a trader control a larger position than the cash posted as collateral. That structure makes losses relative to posted capital larger and faster when price moves against the position.

A broker sets margin requirements so the account retains enough equity to support open positions. If losses reduce account equity toward the maintenance requirement, the account approaches a margin call or liquidation threshold. Once that threshold is breached, positions can be reduced or closed by the broker. The practical consequence is that the trader may be forced out because collateral has been exhausted rather than because the trading signal has changed.

This mechanism matters because forced exits are path dependent. A leveraged position can be closed during a temporary but severe adverse move, locking in losses at a point of stress. If liquidation occurs into a fast market, execution can happen at unfavorable prices relative to the trader’s intended risk plan. In that sense, margin exhaustion can amplify realized losses by turning a mark to market drawdown into an immediate exit.

For systematic traders, margin is therefore not just a financing detail. It is a state variable that can dominate realized outcomes. A strategy may appear acceptable when evaluated only on unlevered returns or on signal quality, yet behave very differently once broker constraints are imposed. Position sizing, portfolio concentration, instrument volatility, and correlation shocks all affect how quickly collateral can be depleted.

This is one reason robustness checks matter in backtesting. Sonar’s backtest overfitting audit is designed to test whether an apparent edge is likely to be genuine or the result of fitting noise. It reports diagnostics including the probability of backtest overfitting, expected maximum Sharpe under multiple testing, and the deflated Sharpe ratio. Those tools help frame whether reported performance survives statistical scrutiny, but they do not replace explicit modeling of leverage and margin rules. If margin constraints are omitted, a backtest can miss liquidation paths that would have terminated positions in live trading.

The deflated Sharpe ratio is relevant as a performance context metric because it adjusts the interpretation of a Sharpe ratio for non normal returns, short sample length, and multiple testing. That matters for leveraged strategies because forced liquidations can create skewed and discontinuous return paths. A raw Sharpe ratio can therefore overstate the reliability of performance if the distribution has been shaped by leverage effects or repeated strategy selection.

Covered in depth in the Strategy research fundamentals pillar hub.