What's the difference between structural and reduced-form credit analysis models?

This is a critical distinction for CFA Level II. Both models estimate the probability of default and loss given default, but they approach the problem from completely different angles.

Structural Models (Merton Model)

The key insight: a company's equity is a call option on its assets. If asset value falls below the debt obligation at maturity, the firm defaults.

• Asset value > Debt → Equity holders keep the residual → No default
• Asset value < Debt → Equity is worthless → Default

The default probability depends on the 'distance to default' — how far asset value is from the default threshold relative to asset volatility.

Inputs needed: Asset value, asset volatility, debt level, risk-free rate, time to maturity.

Reduced-Form Models

These models treat default as a random event governed by a hazard rate (instantaneous probability of default). The hazard rate is estimated from observable market data — primarily credit spreads and bond prices.

The model doesn't ask why a firm defaults; it just estimates the probability based on market signals.

Inputs needed: Credit spread data, recovery rate assumptions, risk-free term structure.

Comparison:

Example:

Runwood Manufacturing has $200M in assets, $150M in debt, and 20% asset volatility. The structural model calculates the probability that a random walk from $200M crosses below $150M before debt maturity — say, 4.8%.

Meanwhile, a reduced-form model looks at Runwood's 5-year CDS spread of 280bp and recovery rate assumption of 40%, and backs out an implied annual default probability of approximately 4.67%. The two approaches should roughly agree if markets are efficient.

CFA Exam Focus: Know that structural models require unobservable inputs (asset value, asset volatility), which is their main limitation. Reduced-form models are more practical for trading desks because they use market prices directly.

For more on credit analysis, explore our CFA Level II community.