Credit Rating
A credit rating is an assessment by a recognized rating agency of the creditworthiness of a borrower — corporation, municipality, sovereign, or structured finance vehicle — expressed as an alphanumeric grade that summarizes the probability of default and, for some scales, the expected loss given default.
Key takeaways
- The three major rating agencies are S&P Global Ratings, Moody's Investors Service, and Fitch Ratings, each with slightly different but largely parallel scales: AAA/Aaa is the highest possible rating, and D/C indicates default.
- Investment-grade bonds are rated BBB-/Baa3 or above; high-yield (speculative grade, 'junk') bonds are rated BB+/Ba1 or below — a distinction that triggers major structural differences in investor access and capital treatment.
- Ratings serve multiple contractual and regulatory functions: investment mandates restrict holdings to IG, Basel capital rules assign lower risk weights to higher-rated exposures, and many structured finance transactions require minimum ratings for collateral and notes.
- Credit ratings are opinions, not recommendations or guarantees of performance; they famously failed to anticipate the deterioration of many AAA-rated structured products before the 2008 financial crisis, leading to regulatory reforms.
- A ratings downgrade below investment grade ('fallen angel') can trigger forced selling from IG-mandated investors and index exclusion, creating mechanical spread widening that often overshoots fundamental deterioration.
Explanation
Credit ratings emerged in the early 20th century as the U.S. bond market grew beyond the capacity of individual investors to evaluate issuers independently. John Moody published the first systematic railroad bond ratings in 1909; S&P (then Poor's) followed. Today the three major agencies (S&P, Moody's, Fitch) collectively rate tens of thousands of issuers and hundreds of thousands of securities globally, with their scales embedded in regulatory frameworks, investment mandates, and contractual triggers worldwide.
The rating scales span from the highest quality to default. S&P: AAA, AA+, AA, AA-, A+, A, A-, BBB+, BBB, BBB- (investment grade) | BB+, BB, BB-, B+, B, B-, CCC+, CCC, CCC-, CC, C, D (speculative/default). Moody's uses Aaa, Aa1, Aa2, Aa3, A1, A2, A3, Baa1, Baa2, Baa3 (investment grade) | Ba1, Ba2, Ba3, B1, B2, B3, Caa1, Caa2, Caa3, Ca, C (speculative/default). The dividing line at BBB-/Baa3 is functionally the most important in fixed income markets: it determines index eligibility (most IG indices require minimum BBB-), regulatory capital treatment, and the permitted investment universe for the majority of institutional investors.
The rating process involves both quantitative and qualitative analysis. Agencies analyze financial metrics (leverage, coverage, liquidity, profitability), business risk (industry structure, competitive position, geographic diversification), management and governance, and the issuer's funding access and financial flexibility. The analysis culminates in a rating committee deliberation that balances all factors and determines the final rating with a stable, positive, or negative outlook (or 'CreditWatch/RatingWatch' designation indicating potential near-term change).
Structured finance ratings use different methodologies: agencies model the collateral pool's expected default frequency (EDF) and loss severity, apply stresses (Great Depression-scale for AAA), and determine the credit enhancement required for each rating level. This quantitative, model-driven approach contrasts with the more judgmental process for corporate ratings — and proved inadequate for complex structured products where correlations among subprime mortgages were dramatically underestimated before 2008.
The regulatory reliance on ratings has declined since the GFC following Dodd-Frank Act mandates to reduce mechanistic references to credit ratings in U.S. regulations. However, ratings remain deeply embedded in practice: the IG/HY divide continues to drive enormous capital flows, as forced selling by IG-mandated investors when a 'fallen angel' is downgraded can depress bond prices well below fundamental value — creating opportunities for flexible capital (hedge funds, crossover funds) to purchase at distressed levels. Historically, fallen angel bonds have delivered superior forward returns relative to original-issue HY bonds, compensating investors for absorbing forced-seller flows.
Formula
Implied Default Probability ≈ Credit Spread / (1 - Recovery Rate); Expected Loss = PD × LGD
Example
In March 2020, Ford Motor Company was downgraded from BBB- to BB+ by S&P — becoming a 'fallen angel' as COVID-19 devastated auto sales projections. The downgrade triggered mandatory selling by investment-grade fund managers and IG index exclusion, driving Ford's bond spreads from ~250 bps to over 700 bps in a matter of weeks even as Ford maintained adequate near-term liquidity. A hedge fund specializing in fallen angels purchased Ford's 2027 bonds at 72 cents on the dollar (yield ~11%) based on its analysis that Ford's substantial cash position ($35B+), undrawn credit lines, and essential product demand made near-term default highly unlikely despite the elevated spread. By year-end 2020, as markets stabilized and Ford demonstrated financial resilience, the bonds recovered to near 95 cents — a 32% return in under 9 months for investors who absorbed the forced-seller technical pressure at the time of the downgrade.
Related terms
Bond Credit Enhancement Default Diversification Dodd Frank Act Equity Tranche Fallen Angel Flat Yield Curve Hedge Fund Investment Grade Leverage Liquidity