Credit Ratings: How Agencies Grade Borrowers

What Credit Ratings Are

A credit rating is an assessment of the creditworthiness of a bond issuer — the likelihood that the issuer will make all promised interest and principal payments on time. Ratings are assigned by Nationally Recognized Statistical Rating Organizations (NRSROs), the most prominent being Moody's Investors Service, S&P Global Ratings, and Fitch Ratings.

Ratings are assigned to both issuers (the borrowing entity) and specific debt issues (individual bonds). They are based on analysis of financial statements, industry conditions, management quality, and economic outlook.

The Rating Scale

S&P and Fitch use a letter scale from AAA (highest quality) to D (default). Moody's uses a similar scale with slightly different notation (Aaa, Aa, A, Baa, Ba, B, Caa, Ca, C). Ratings from BBB- (S&P/Fitch) or Baa3 (Moody's) and above are considered investment grade. Ratings below these thresholds are speculative grade, commonly called high yield or junk.

Within each major category, ratings are modified by + or - (S&P/Fitch) or 1, 2, 3 (Moody's) to indicate relative standing. AA+ is higher quality than AA, which is higher than AA-.

Investment Grade vs. High Yield

The investment grade/high yield distinction has significant practical consequences. Many institutional investors — pension funds, insurance companies, money market funds — are restricted by regulation or mandate to holding only investment grade securities. When a bond is downgraded from investment grade to high yield (a fallen angel), forced selling by these investors can cause sharp price declines.

High yield bonds offer higher interest rates to compensate for higher default risk. The spread between high yield and Treasury yields (the high yield spread) is a widely watched indicator of credit market conditions and risk appetite.

Sovereign Ratings

Rating agencies also rate sovereign debt — bonds issued by national governments. A sovereign downgrade can raise borrowing costs for the entire country and affect the ratings of domestic banks and corporations. The U.S. lost its AAA rating from S&P in 2011 and from Fitch in 2023, though it retains AAA from Moody's.

Limitations of Ratings

Credit ratings have well-documented limitations. They are lagging indicators — agencies often downgrade issuers after problems are already reflected in market prices. The 2008 financial crisis exposed serious failures in the rating of structured products (mortgage-backed securities). Ratings are opinions, not guarantees, and should be one input among many in credit analysis.

Educational Context

This article is for educational purposes only and does not constitute investment advice. Credit ratings are subject to change and do not guarantee the safety of any investment.