Bond ratings are letter grades assigned by independent agencies to estimate how likely a bond issuer is to pay you back on time and in full. The top grade, AAA (or Aaa in Moody’s notation), signals minimal default risk; the bottom of the scale, C or D, means the issuer is in or near default. Those letters drive the interest rate the borrower pays, whether large institutions are even allowed to buy the bond, and how the bond’s price behaves in the secondary market.
The Rating Scales From Top to Bottom
S&P Global Ratings and Fitch Ratings use the same letter system. Moody’s Investors Service uses a slightly different notation that maps to the same levels of credit quality. The scales run from strongest at the top to default at the bottom:
- AAA (S&P/Fitch) or Aaa (Moody’s): highest quality, with extremely strong ability to meet financial commitments and minimal default risk1Moody’s Investors Service. Moody’s Rating Scale and Definitions
- AA or Aa: high quality, very low credit risk
- A: upper-medium grade, low credit risk
- BBB or Baa: medium grade, moderate credit risk; the lowest tier still considered investment grade
- BB or Ba: speculative, substantial credit risk
- B: highly speculative, high credit risk
- CCC or Caa: poor standing, very high credit risk
- CC or Ca: likely in or very near default
- C or D: the issuer has failed to meet its obligations
Modifiers Within Each Grade
A single letter covers a range of quality, so agencies add modifiers to show where a bond falls inside that range. S&P and Fitch append a plus or minus sign, so AA+ sits above AA, which sits above AA−. Moody’s uses the numbers 1, 2, and 3 for the same purpose, where Aa1 is the strongest within the Aa category and Aa3 is the weakest. Modifiers are not applied at the very top of the scale or at the very bottom.1Moody’s Investors Service. Moody’s Rating Scale and Definitions
When Agencies Disagree
The agencies do not always land on the same grade. Roughly half of all bonds carry ratings that differ by at least one notch between agencies, and about 13 percent differ by a full letter grade. Bonds with split ratings tend to carry slightly higher yields — research has found a premium of about 7 basis points on average, rising to 15 or 20 basis points for larger disagreements — because the uncertainty itself is a form of risk.
The Investment-Grade Line
The most consequential threshold in the rating system falls between BBB− (or Baa3) and BB+ (or Ba1). Everything at or above BBB−/Baa3 is “investment grade.” Everything below is “speculative grade,” sometimes called high-yield or junk.2S&P Global Ratings. Understanding Credit Ratings
This boundary carries real regulatory weight. Federal banking rules require national banks to hold only securities that qualify as investment grade, defined as having adequate capacity to meet financial commitments with low default risk.3eCFR. 12 CFR Part 1 – Investment Securities Insurance companies face similar restrictions under state capital rules set through the National Association of Insurance Commissioners. Pension funds and other fiduciary accounts often have their own policies or legal mandates limiting holdings to investment-grade bonds. A large share of the bond market’s biggest buyers are effectively barred from purchasing speculative-grade debt.
Fallen Angels
When a bond is downgraded from investment grade to speculative grade, it becomes what the market calls a fallen angel. Institutional holders restricted to investment-grade securities may be forced to sell, flooding the market with supply and pushing the price down. The issuer’s borrowing costs jump, and issuing new debt gets harder.4European Central Bank. Understanding What Happens When Angels Fall Markets often price in the downgrade before it officially happens, with credit default swap costs rising well in advance, but the actual loss of the last investment-grade rating can still trigger a further drop as forced selling takes hold.
What Goes Into a Rating
Rating analysts combine quantitative data with qualitative judgment. The core financial work focuses on balance sheets, income statements, and cash flow patterns across different economic conditions. Analysts look at how much debt the issuer carries relative to its revenue, whether earnings are stable or volatile, and whether the issuer has enough liquid assets to cover near-term obligations. Industry-specific factors matter too: a utility company faces different risks than a technology startup.
Environmental, social, and governance factors have become a formal part of the process. Moody’s, for example, assigns ESG-related issuer profile scores and credit impact scores that feed into the overall rating, assessing exposure to issues like climate risk, labor practices, and corporate governance quality on a standardized scale.
Outlooks and Watchlists
A bond rating is not a one-time verdict. Agencies monitor issuers continuously and signal when a change may be coming through two mechanisms.
An outlook reflects the agency’s view of where the rating is headed over the next one to two years. S&P assigns an outlook when there is roughly a one-in-three chance of a rating change within that window.5S&P Global Ratings. Criteria on Use of CreditWatch and Outlooks Clarified Moody’s uses four categories: positive, negative, stable, and developing, the last of which applies when the direction depends on a specific pending event.6Moody’s Investors Service. Moody’s Rating Symbols and Definitions A negative outlook does not guarantee a downgrade, but it tells you the agency sees meaningful risk of one.
A watchlist placement is more urgent. S&P places a rating on CreditWatch when there is at least a 50 percent chance of a change within 90 days, typically triggered by an unexpected event like a merger announcement, a sudden earnings drop, or regulatory action.5S&P Global Ratings. Criteria on Use of CreditWatch and Outlooks Clarified Moody’s calls the equivalent Rating Under Review. While a bond is on a watchlist, the normal outlook designation is suspended until the review concludes.6Moody’s Investors Service. Moody’s Rating Symbols and Definitions
How Ratings Shape What You Earn
The relationship between a bond’s rating and its yield is direct: riskier borrowers pay more. A top-tier issuer can borrow at a lower interest rate because buyers are confident they will be repaid. As the rating drops, buyers demand higher yields to compensate for the greater chance of loss. The gap between the yield on a risky bond and a comparable safe bond is the credit spread, and it widens as ratings fall.
Ratings also affect how easily you can buy or sell a bond on the secondary market. Higher-rated bonds tend to trade more frequently and with tighter bid-ask spreads, so you lose less to trading costs when entering or exiting a position. Speculative-grade bonds are less liquid, and a significantly larger portion of their yield spread compensates investors for the difficulty of selling quickly rather than for default risk alone.
Default Rates by Rating
The rating system’s track record shows a strong link between grades and actual defaults. S&P’s historical data puts a BBB-rated company’s three-year cumulative default rate at about 0.91 percent, while a BB-rated company defaults at 4.17 percent over the same period. The rates escalate sharply further down: B-rated issuers default at 12.41 percent, and CCC/CC-rated issuers default at 45.67 percent over three years.2S&P Global Ratings. Understanding Credit Ratings
For the broader market, S&P projected the U.S. trailing-12-month speculative-grade corporate default rate to reach 3.75 percent by December 2026, with Europe’s rate falling to 3.25 percent.7S&P Global Ratings. The Ratings View – Feb. 18, 2026 When defaults do occur, recovery rates depend heavily on where the bond sits in the issuer’s capital structure. Secured bonds backed by specific assets historically recover around 50 percent of face value. Unsecured and subordinated bonds recover closer to 27 to 33 percent.
Who Assigns the Ratings
Three firms dominate the industry: S&P Global Ratings, Moody’s Investors Service, and Fitch Ratings. Together they issue the vast majority of credit ratings used worldwide. Seven other agencies also hold Nationally Recognized Statistical Rating Organization status with the Securities and Exchange Commission, bringing the total to ten as of December 2024. Some of these smaller firms focus on specific sectors; A.M. Best specializes in insurance companies, and Kroll Bond Rating Agency covers a broad range of corporate and structured finance products.8U.S. Securities and Exchange Commission. Current NRSROs
The Issuer-Pay Conflict
The most persistent criticism of the rating system centers on how the agencies get paid. Under the dominant issuer-pay model, the company or government issuing the bond pays the agency for the evaluation, creating a tension between producing honest assessments and keeping clients happy.9U.S. Government Accountability Office. Credit Rating Agencies – Alternative Compensation Models for Nationally Recognized Statistical Rating Organizations
That conflict was exposed during the 2008 financial crisis. Agencies had assigned their highest grades to mortgage-backed securities and collateralized debt obligations built on pools of risky loans. When those loans defaulted at unexpected rates, previously AAA-rated investments became essentially unmarketable. Investigations found that the agencies’ models were based on historical data that did not account for a nationwide decline in home prices, and that the desire to retain business encouraged agencies to issue favorable ratings to the institutions paying for them.10FDIC. Crisis and Response – An FDIC History, 2008-2013
Congress responded with the Dodd-Frank Act in 2010, which imposed mandatory separation of the ratings function from sales and marketing, internal controls over rating methodologies, public disclosure of rating performance statistics, and minimum training standards for analysts.11U.S. Securities and Exchange Commission. Implementing the Dodd-Frank Wall Street Reform and Consumer Protection Act The SEC conducts annual examinations of registered agencies and publishes staff reports on its findings.12U.S. Securities and Exchange Commission. 2024 Staff Report on Nationally Recognized Statistical Rating Organizations The issuer-pay model remains the industry standard, and no alternative compensation structure has been widely adopted.
How to Look Up a Bond’s Rating
If you own bonds or are considering buying one, you can check the current rating through several channels. FINRA’s TRACE system lets you search any corporate or agency bond by CUSIP number or ticker symbol and view trade data alongside rating information.13FINRA. Bond Page Each of the three major agencies publishes ratings on its own website, though some require a free account for detailed reports. Most brokerage platforms display the current rating from at least one agency on a bond’s detail page.
A rating reflects the agency’s view at the time it was issued or last updated, not a guarantee of future performance. Checking for recent outlook changes or watchlist placements gives you a fuller picture than the letter grade alone. If a bond you hold is placed on negative watch, that does not mean you need to sell, but it is worth understanding the reason and following the review to its conclusion.