Table of Contents
A credit rating is a forward-looking opinion issued by a Nationally Recognised Statistical Rating Organisation on the relative creditworthiness of a debt issuer or a specific debt obligation, expressing the agency's assessment of the probability that the issuer will meet its financial commitments in full and on time. Credit ratings are the foundational credit risk classification system of global fixed income markets, determining which institutional investors may hold which securities, setting borrowing costs across the investment spectrum, and directly influencing the capital requirements imposed on financial institutions by banking regulators.
Three rating agencies dominate the global credit rating industry: Moody's Investors Service, Standard and Poor's Global Ratings, and Fitch Ratings. Together they control approximately ninety-five percent of the global ratings business and are collectively known as the Big Three. In addition to the Big Three, as of March 2024 there are ten total firms registered with the SEC as Nationally Recognised Statistical Rating Organisations, including A.M. Best, Kroll Bond Rating Agency, and Morningstar Credit Ratings.
The NRSRO designation originated in 1975 when the SEC adopted it to identify rating agencies whose opinions would be accepted for purposes of applying the net capital rule to broker-dealers under SEC Rule 15c3-1 under the Securities Exchange Act of 1934. The net capital rule required broker-dealers to apply different haircuts to debt securities of different credit qualities, and the SEC needed an authoritative standard to determine what qualified as investment grade. Moody's, Standard and Poor's, and Fitch were the first three recognised, based on their established market presence and widespread use by investors.
The Credit Rating Agency Reform Act of 2006 formalised the NRSRO registration process, requiring agencies seeking NRSRO status to register with the SEC and comply with specific disclosure and conduct requirements. The Dodd-Frank Wall Street Reform and Consumer Protection Act of 2010 created the SEC's Office of Credit Ratings to oversee NRSROs, conduct regular examinations, and enforce compliance with SEC rules. The Office of Credit Ratings represents the most comprehensive direct regulatory supervision of rating agencies in United States history.
Moody's and Standard and Poor's use parallel but distinct notation systems that candidates must know precisely.
Moody's long-term rating scale descends from Aaa — its highest rating, assigned to obligations of exceptional creditworthiness — through Aa, A, Baa, Ba, B, Caa, Ca, and C. Moody's appends numeric modifiers 1, 2, and 3 to each category from Aa through Caa, where 1 indicates the higher end of the category, 2 the middle, and 3 the lower end. Baa3 is therefore the lowest investment grade rating in the Moody's system.
Standard and Poor's and Fitch use an alphabetic scale with plus and minus modifiers. Their highest rating is AAA, descending through AA, A, BBB, BB, B, CCC, CC, C, and D for default. The plus and minus modifiers subdivide each major category, so BBB plus is the highest and BBB minus is the lowest subcategory within the BBB category. BBB minus is the lowest investment grade rating in the S&P and Fitch systems.
The investment grade threshold is Baa3 at Moody's and BBB minus at S&P and Fitch. This threshold is not merely a labelling convention. It is a regulatory and contractual boundary that determines which securities pension funds, insurance companies, bank trust departments, and money market funds may purchase. Many institutional mandates explicitly prohibit below-investment-grade holdings. When a bond falls below the threshold — a fallen angel — it is sold by institutions whose mandates prevent them from holding speculative grade paper regardless of the price, often creating significant selling pressure independent of any change in the bond's fundamental value.
A credit rating is a relative measure of default risk and expected loss severity. Moody's describes its ratings explicitly as forward-looking opinions of the relative credit risks of financial obligations. The rating does not measure liquidity risk, interest rate risk, market risk, or any risk other than credit risk. It does not guarantee the rated obligation will be repaid, and it does not constitute investment advice. It is a professional opinion, subject to revision as circumstances change.
Two related but distinct concepts underlie rating methodology. Probability of default is the likelihood the issuer will fail to make a scheduled payment within a defined time horizon. Loss given default is the expected proportion of principal and accrued interest that would not be recovered if a default occurred, reflecting the seniority of the obligation in the capital structure and the quality of any collateral. Combined, probability of default and loss given default determine expected loss, which is the metric most directly relevant to bond investors and the one that rating methodologies are ultimately designed to estimate.
The rating process typically begins when an issuer engages a rating agency and provides detailed financial information — audited financial statements, management presentations, business plans, and often access to senior management. The rating agency assigns a team of analysts who conduct quantitative analysis of the issuer's financial metrics and qualitative assessment of its business position, competitive environment, management quality, and industry dynamics.
For corporate ratings, analysts examine key financial ratios including debt to EBITDA, interest coverage, free cash flow generation, and return on invested capital, benchmarking these against the distribution observed across similarly rated issuers. The qualitative assessment addresses the competitive position of the business, the stability and predictability of cash flows, the depth and experience of management, and governance practices. The analysts present their findings and a proposed rating to a rating committee, which makes the final determination by majority vote. The issuer is notified of the proposed rating before it is published, allowing the issuer to provide additional factual information, though not to negotiate the rating outcome.
Ratings are then monitored continuously. Rating agencies place issuers on Watchlist or CreditWatch — positive or negative — when a specific event or development makes a rating change possible in the near term. A negative Watchlist indicates the agency is reviewing for a potential downgrade, while a positive Watchlist indicates potential upgrade. Outlook assignments — stable, positive, negative, or developing — indicate the likely direction of the rating over the medium term, typically twelve to twenty-four months.
The dominant business model of the major rating agencies is the issuer-paid model: the company whose debt is being rated pays the rating agency for the rating. This creates a structural conflict of interest that has been extensively documented, most acutely in the period preceding the 2008 financial crisis. Rating agencies assigned AAA ratings to thousands of structured finance securities backed by subprime mortgage loans, earning large fees from the issuers and arrangers of those securities. When the underlying mortgage loans defaulted in large numbers, those AAA ratings proved catastrophically inaccurate, and a Securities and Exchange Commission examination found that rating agencies had been aware of deteriorating underwriting standards while continuing to issue their highest ratings.
The Credit Rating Agency Reform Act of 2006 and the Dodd-Frank Act imposed new conflict-of-interest disclosure requirements and prohibited certain practices that could compromise rating integrity. The SEC's Office of Credit Ratings examines NRSROs specifically for evidence that commercial pressures are influencing rating outcomes. The Dodd-Frank Act also required the SEC to study the feasibility of alternative compensation models and mandated periodic review of how credit ratings are used in federal regulations.
Beyond their direct market function, credit ratings are embedded in federal regulation at multiple levels, though the Dodd-Frank Act directed federal agencies to reduce their regulatory reliance on NRSRO ratings and develop alternative standards of creditworthiness.
The SEC's net capital rule under Rule 15c3-1 continues to apply different haircuts to broker-dealer bond inventories based on credit quality, using rating-based criteria to determine the applicable haircut percentages. SEC Rule 2a-7 governing money market fund investments permits these funds to hold only securities meeting minimum quality standards, defined in part by reference to NRSRO ratings. Bank capital requirements under the Basel framework permit banks that use the standardised approach to calculate risk weights for credit exposures by reference to external credit ratings.
Pension funds and insurance companies are subject to state investment regulations that in many cases restrict portfolio holdings to investment grade securities, effectively making the Baa3 or BBB minus threshold a hard constraint on the investable universe for these large pools of capital. The practical consequence is that the investment grade boundary creates a sharp discontinuity in the population of potential buyers for any given security, producing significant price discontinuities at and near the threshold.
Rating agencies publish separate short-term rating scales for debt instruments with original maturities of one year or less, most importantly commercial paper. At Moody's, the highest short-term rating is Prime-1, followed by Prime-2 and Prime-3. At Standard and Poor's and Fitch, the highest is A-1, followed by A-2 and A-3. Only Prime-1 and A-1 issuers — referred to as tier-one issuers — can place commercial paper with money market funds that are restricted under SEC Rule 2a-7 to the highest quality instruments. Prime-2 and A-2 issuers qualify as tier-two and face a somewhat smaller investor base and marginally higher spreads. Commercial paper issuers below tier-two cannot access the money market fund investor base at all.
Rating agencies assign credit ratings to sovereign governments as well as corporate entities, assessing the ability and willingness of national governments to service their debt obligations. Sovereign ratings incorporate factors that do not apply to corporate analysis: the government's taxing power and fiscal flexibility, monetary policy capacity, currency regime, external debt burden, political stability, and institutional quality. The distinction between ability to pay and willingness to pay is particularly important in sovereign analysis — a government that controls its own currency can in principle always print money to service local-currency debt but may choose to default for political reasons, and a government borrowing in foreign currency faces genuine constraints on its ability to service obligations if foreign exchange reserves are insufficient.
Sovereign ratings act as a ceiling on the ratings of entities domiciled within the sovereign's jurisdiction, because a corporate issuer operating within a country faces the same country-specific risks — currency controls, nationalisation, systemic banking crises — that constrain sovereign creditworthiness. A corporation cannot in principle carry a higher credit rating than the sovereign of the country in which it operates, except in limited circumstances where the corporation has significant foreign currency revenues and assets outside the sovereign's jurisdiction.
Credit ratings are tested on the SIE, Series 7, and Series 65 examinations primarily in the context of the investment grade threshold, the specific rating scales of Moody's and Standard and Poor's, the role of NRSROs, and the impact of ratings on institutional investment eligibility and bond pricing.
The core points to retain are these: a credit rating is a forward-looking opinion of relative creditworthiness issued by a Nationally Recognised Statistical Rating Organisation registered with and regulated by the SEC; the Big Three NRSROs are Moody's, Standard and Poor's Global Ratings, and Fitch Ratings, controlling approximately ninety-five percent of the global market; the investment grade threshold is Baa3 at Moody's and BBB minus at Standard and Poor's and Fitch, with Moody's using numeric modifiers 1 through 3 and Standard and Poor's and Fitch using plus and minus to subdivide categories; securities rated below the investment grade threshold are speculative grade or high yield, also called junk bonds, and are excluded from the investable universe of many institutional investors whose mandates or regulatory requirements restrict them to investment grade holdings; a fallen angel is a bond downgraded from investment grade to below investment grade, triggering forced selling by investment grade constrained investors regardless of price; the NRSRO designation was created by the SEC in 1975 for purposes of the net capital rule under Rule 15c3-1, and the Credit Rating Agency Reform Act of 2006 formalised the registration process, with the Dodd-Frank Act creating the Office of Credit Ratings to conduct ongoing NRSRO examinations; the dominant issuer-paid business model creates structural conflicts of interest that were exposed acutely in the 2008 financial crisis when AAA ratings on subprime mortgage securities proved catastrophically inaccurate; and short-term ratings at Moody's use the Prime-1 through Prime-3 scale while Standard and Poor's and Fitch use A-1 through A-3, with tier-one issuers at Prime-1 or A-1 having full access to money market fund investors under SEC Rule 2a-7.
