Investment grade bonds are rated by credit rating agencies like Standard & Poor’s (S&P), Moody's, and Fitch. The ratings are based on the issuer’s financial health, historical performance, and overall economic environment. Ratings range from AAA (highest quality, lowest risk) to BBB- (lower quality, higher risk but still considered investment grade). For example:
AAA/Aaa: Highest credit quality, minimal risk.
AA/Aa: High credit quality, very low risk.
A: Strong credit quality, low risk.
BBB/Baa: Adequate credit quality, moderate risk, but still investment grade.
The credit rating on a bond will be associated with the premium or “spread” demanded for holding it: the higher the risk, the more issuers will have to pay investors.