通常海外債比較常見的有三種評等機構：穆迪、標準普爾和惠譽。各自有不同的字母代表不同的可能違約機率。
評等越高的債券，代表越不容易違約，當然並不是絕對的關係，但機率上來說是如此。相對地，這也影響到到期殖利率（即購買時的價格換算每年的殖利率），評等越高，殖利率越低。到期殖利率還會受到產業、發行國家以及公司的名聲等因素的影響。
穆迪評等
- Aaa：最高評等，風險最低，投資者可以預期極高的信用品質和極低的違約風險。
- Aa1, Aa2, Aa3（Aa類）：高信用品質，違約風險低，但略低於Aaa等級。
- A1, A2, A3（A類）：上等信用品質，違約風險仍然相對較低。
- Baa1, Baa2, Baa3（Baa類）：中等信用品質，可能具有某些投機特性，違約風險中等。
- Ba1, Ba2, Ba3（Ba類）：投機等級，信用風險較高。
- B1, B2, B3（B類）：投機等級，信用品質較低，違約風險較大。
- Caa1, Caa2, Caa3（Caa類）：貧弱的信用品質，違約風險非常高。
- Ca：極度貧弱的信用品質，違約風險極高，債券可能已經違約或接近違約。
- C：最低評等，通常表示債券已違約。
解釋一下，如果以穆迪評等來看債券，Aaa的債券到期殖利率絕對比A1的債券低，但相對地也更能保障本金不會因違約或倒債而損失。需要注意的是，數字越低代表評等越高，例如A1的評等比A3高。
標準普爾和惠譽評等
- AAA：最高評等，表示違約風險極低。
- AA：非常高的信用品質，違約風險很低。
- A：高信用品質，違約風險低。
- BBB：良好信用品質，違約風險中等。
- BB, B, CCC, CC, C：投機等級，違約風險較高，其中BB和B表示有可能償還債務，CCC及以下則表示違約風險非常高。
- D：表示債券已經違約。
在AA到CCC的每個主要評等類別中，可以使用「+」或「-」來表示該類別內的相對排名。「+」表示相對較高，「-」表示相對較低。AAA是最高評等，因此沒有AAA+或AAA-的標示。
此外，評等展望也是評估的一部分，可能包括：
- Positive：評等有上升趨勢。
- Negative：評等有下降趨勢。
- Stable：評等可能不會改變。
- Developing：評等可能上升或下降。
投資等級債
投資等級債相對穩健且風險較低，台灣的銀行理論上只會代理這類型的債券。穆迪評等在Baa以上的債券屬於投資等級，標準普爾和惠譽評等在BBB以上的則屬於投資等級。
建議在挑選債券時應以投資等級債為優先，即使其到期殖利率較低，仍相對安全。
非投資等級債
非投資等級債則是指評等在投資等級以下的債券，這類債券在基金中常見，違約機率較高，基金經理人需密切關注是否要立即拋售以避免違約風險（例如無法支付利息或倒債）。
這是對債券評等的基本介紹，希望對需要了解的人有所幫助。
Typically, there are three major credit rating agencies for foreign bonds: Moody’s, Standard & Poor’s (S&P), and Fitch. Each agency uses different letter ratings to represent varying probabilities of default.
The higher the bond rating, the less likely a default will occur. While this is not an absolute rule, statistically, it holds true. Consequently, the yield to maturity, which is the annual yield based on the purchase price, tends to be lower for higher-rated bonds. The yield to maturity is also influenced by the industry, issuing country, and the company’s reputation.
Moody’s Ratings
- Aaa: The highest rating, representing minimal risk. Investors can expect excellent credit quality and an extremely low risk of default.
- Aa1, Aa2, Aa3 (Aa category): High credit quality, with a low risk of default, but slightly lower than Aaa.
- A1, A2, A3 (A category): Upper-medium credit quality, still relatively low risk of default.
- Baa1, Baa2, Baa3 (Baa category): Medium credit quality, may have speculative elements, with moderate default risk.
- Ba1, Ba2, Ba3 (Ba category): Speculative grade with higher credit risk.
- B1, B2, B3 (B category): Speculative grade with lower credit quality and a higher risk of default.
- Caa1, Caa2, Caa3 (Caa category): Poor credit quality, very high risk of default.
- Ca: Extremely poor credit quality, extremely high risk of default, bonds may already be in or near default.
- C: The lowest rating, typically indicating the bond has defaulted.
To explain further, using Moody’s ratings to evaluate bonds: a bond rated Aaa will have a lower yield to maturity compared to one rated A1, but it also offers more security against default or bankruptcy. It is important to note that in Moody’s system, lower numbers represent higher ratings (e.g., A1 is higher than A3).
Standard & Poor’s and Fitch Ratings
- AAA: The highest rating, indicating extremely low default risk.
- AA: Very high credit quality, with very low default risk.
- A: High credit quality, with low default risk.
- BBB: Good credit quality, with moderate default risk.
- BB, B, CCC, CC, C: These are speculative-grade ratings, indicating higher default risk. BB and B suggest the ability to repay debt, while CCC and below suggest a very high default risk.
- D: Indicates the bond has already defaulted.
Within each major rating category from AA to CCC, “+” or “-” can be used to indicate relative ranking within the category, where “+” indicates a higher standing and “-” indicates a lower standing. However, the highest rating of AAA does not have AAA+ or AAA-.
In addition, rating outlooks are part of the evaluation and may include:
- Positive: Indicates an upward trend in ratings.
- Negative: Indicates a downward trend in ratings.
- Stable: Indicates the rating is unlikely to change.
- Developing: Indicates the rating may move up or down in the future.
Investment-Grade Bonds
Investment-grade bonds are relatively stable and carry lower risk. In theory, Taiwanese banks only handle this type of bond. For Moody’s, bonds rated Baa or higher are considered investment-grade, while for S&P and Fitch, bonds rated BBB or higher qualify as investment-grade.
It is advisable to prioritize investment-grade bonds when selecting bonds, even if they offer lower yields to maturity, as they are relatively safer.
Non-Investment-Grade Bonds
Non-investment-grade bonds, or speculative-grade bonds, are those rated below investment grade. These bonds are common in funds and carry a higher risk of default. Fund managers need to closely monitor whether to sell non-investment-grade bonds to avoid defaults, such as missed interest payments or bankruptcy.
This concludes the explanation of bond ratings. I hope it provides helpful information for those in need.
