Distance to Default (DD) in the Black-Scholes model measures the number of standard deviations by which the value of a firm's assets is above its debt obligations at a specific time (usually at the debt's maturity). DD is a critical measure in determining the likelihood of a firm defaulting on its debt. A higher DD suggests a lower risk of default, indicating a healthier financial position of the firm.

A is incorrect because the difference between a firm's total assets and total liabilities is not what DD measures. DD is concerned with the relative position of the firm's assets to its debt obligations in terms of standard deviations, not just the absolute difference in value.

C is incorrect because DD does not measure the gap between the market value of equity and the face value of debt. While these values are relevant in the Black-Scholes model, DD specifically relates to the asset value in relation to the debt level.

D is incorrect because DD is not a measure of time but a measure of risk distance. It does not denote the time until debt maturity but rather the risk buffer before default.

Things to Remember

• DD is a crucial metric for assessing credit risk, as it provides an indication of a firm's buffer against default under current financial conditions.
• The calculation of DD involves key variables such as the current market value of the firm's assets, its debt level, the expected asset return, and the volatility of the assets.
• In practice, DD is particularly useful for analysts in estimating credit risk for corporate bonds and loans, especially for firms with publicly traded equity, where market data is more readily available.