How Credit Ratings Work: S&P, Moody's, Fitch

Introduction

A credit rating compresses everything a lender needs to worry about, cash flow durability, leverage, liquidity, industry cyclicality, country risk, and management behavior, into a short string of letters. AA- tells a portfolio manager more in two characters than a fifty-page credit memo does in an afternoon, which is precisely why ratings sit at the center of how the corporate debt market is priced, documented, indexed, and regulated. Three firms, S&P Global Ratings, Moody's, and Fitch Ratings, produce the overwhelming majority of those letters for corporate borrowers worldwide.

For anyone interviewing in debt capital markets, leveraged finance, credit research, or restructuring, ratings are not background trivia. They determine which desk runs a financing, how wide the bond prices, whether a pension fund is even allowed to buy it, and what happens mechanically when the company stumbles. Interviewers know this, so the questions come constantly: what is the difference between an issuer rating and a bond rating, why does a one-notch downgrade at the BBB- line matter so much more than a one-notch downgrade at A+, and who actually pays for the rating in the first place. This post walks through the scales, the analysis behind them, how individual instruments get notched away from the issuer, what outlooks and watch listings signal, and how downgrades transmit into pricing and covenants.

The single most useful thing to have memorised is the mapping between the three scales. S&P and Fitch share notation almost exactly; Moody's uses a different convention that trips up candidates who only ever learned one.

Two details in that table are worth internalising. First, Moody's has no separate D category: a defaulted issuer simply sits at C, while S&P and Fitch both split the default category: S&P assigns SD (selective default) when the issuer keeps paying its other obligations and D for a general default, and Fitch uses RD and D the same way. Second, the modifiers work differently, with S&P and Fitch appending plus and minus signs and Moody's appending 1, 2, and 3, where 1 is the strongest position within a category. Saying "Baa-plus" in an interview is an instant tell.

The letters are not a continuous risk scale in the way a probability would be. They are ordinal buckets, each covering a range of default likelihoods that widens sharply as you move down.

AAA and AA: The Thin Air at the Top

The AAA category is now almost empty in the corporate world. A handful of names, mostly cash-rich technology and pharmaceutical businesses with fortress balance sheets, carry the top rating from any agency, and the count has fallen steadily for four decades as companies learned that an optimal capital structure usually involves more debt than a AAA rating tolerates. Losing the top rating is rarely a crisis; it is often a deliberate choice to fund buybacks or acquisitions.

Sovereigns dominated the AAA population for years, and even there the picture has changed. Moody's downgraded the United States from Aaa to Aa1 on 16 May 2025, following S&P in 2011 and Fitch in 2023, which left no major agency assigning the US government a top rating for the first time in over a century. The Moody's rating action on the United States is a useful case study in how agencies articulate a downgrade rationale, in that instance persistent deficits and a rising interest burden rather than any change in ability to print currency.

A and BBB: Where Most Big Companies Live

The A and BBB categories hold the bulk of the large-cap corporate universe. An A rated issuer is a strong, diversified business with conservative leverage and reliable access to funding. A BBB issuer is still investment grade but has less headroom, and this is the band where financial policy matters most, because a single debt-funded acquisition can push an issuer from BBB+ to BBB- and put it one notch from the high yield market.

The BBB band has grown into a very large share of the investment grade index over the past two decades, which is why credit strategists watch it obsessively. A recession that pushes even a modest fraction of BBB issuers below the line floods a much smaller high yield market with paper.

Below the Line: BB, B, CCC and Default

Below the line, BB issuers are typically sound operating businesses carrying more debt than the investment grade market tolerates, often after a leveraged buyout or a large acquisition. B issuers are the core of the leveraged finance market: sponsor-owned companies, mid-size businesses, and growth stories where the credit case rests on deleveraging over time. CCC is where the market starts pricing a real probability of restructuring within a few years rather than a remote tail risk. If you are recruiting for a levered credit seat, our overview of how leveraged finance works covers the deal flow that sits in exactly this part of the scale.

The bottom three rungs describe distress in progress rather than distress in prospect. CC and C signal that default is highly likely or effectively under way, often because a distressed exchange has been announced. D at S&P and D or RD at Fitch confirm that a payment has been missed or an exchange has closed at a loss to the original terms. Restructuring bankers spend their careers in these three rungs.

Every notch on the scale carries information, but only one boundary functions as a switch. BBB- at S&P and Fitch, equivalent to Baa3 at Moody's, is the lowest investment grade rating. BB+ and Ba1 are the highest speculative grade ratings. One notch separates them, and the credit quality difference is usually marginal.

What Actually Changes at the Line

What changes is not the company but the rulebook that governs who may hold its paper. Insurance regulators assign capital charges by rating band. Pension mandates and separately managed account guidelines routinely prohibit speculative grade holdings. Index providers use the line to sort bonds into investment grade and high yield benchmarks, and the passive and benchmark-tracking money that follows those indices has to act. The result is that a single notch triggers a change of ownership, not just a change of price. Our detailed comparison of investment grade and high yield bonds walks through how the two markets differ on spreads, covenants, and buyer base once a credit lands on either side.

Split Ratings and the Middle-Rating Rule

Agencies frequently disagree, and the market needs a tiebreaker. Index providers publish one. The Bloomberg US Corporate Index, the standard investment grade benchmark, requires a bond to be rated Baa3/BBB-/BBB- or higher using the middle rating of Moody's, S&P, and Fitch; where only two agencies rate the bond, the lower of the two applies; where only one does, that rating stands. The index also imposes a minimum outstanding size of $300 million per bond, which is why small deals never appear in benchmark statistics.

Split Rating

A situation where two or more agencies assign different ratings to the same issuer or bond, for example Baa3 from Moody's and BB+ from S&P. Split ratings matter most around the investment grade boundary, because index providers and investment mandates apply tiebreaker rules (commonly the middle of three ratings, or the lower of two) to decide which side of the line the bond falls on.

A credit that is rated investment grade by two agencies and speculative grade by the third is often called a crossover credit, and it trades at a spread somewhere between the two markets while investors argue about which agency is right. Sitting on a split rating is uncomfortable for a treasurer, because the cost of funding depends partly on which agency moves next.

The public methodologies of all three agencies follow a similar architecture: assess the business, assess the balance sheet, combine the two into a starting point, then adjust.

Business Risk Profile

The business risk profile captures how volatile and defensible the company's earnings are before you look at a single debt figure. S&P builds it from three inputs: country risk (where the assets and cash flows sit), industry risk (cyclicality, barriers to entry, growth, and competitive intensity), and competitive position (scale, diversification, market share, cost position, and profitability relative to peers).

This is why two companies with identical leverage can be rated three notches apart. A regulated utility with contracted revenue and a mining company with commodity-linked earnings do not deserve the same rating at 4x debt to EBITDA, because the utility's cash flows barely move through a cycle and the miner's can halve.

Financial Risk Profile

The financial risk profile is the quantitative side, built on cash flow and leverage ratios calculated on the agency's own adjusted figures rather than the numbers as reported. The two workhorses are leverage, usually total debt to EBITDA, and interest coverage:

Agencies also lean heavily on cash flow measures that a ratio-only candidate forgets: funds from operations to debt, free operating cash flow to debt, and discretionary cash flow after dividends and capital expenditure. Note that agencies adjust the inputs before calculating anything, capitalizing operating leases and pension deficits, deconsolidating certain joint ventures, and haircutting cash they consider trapped or operational. If you want to see where those adjustments come from, our walkthrough of how to read SEC filings covers the footnotes analysts mine for exactly this purpose.

Modifiers: Liquidity, Financial Policy and Management

The business and financial risk profiles combine into what S&P calls an anchor, and the anchor is then moved up or down by modifiers: liquidity, financial policy, diversification, management and governance, and a comparable ratings analysis against peers. The weighting is not symmetric across the scale. In S&P's corporate methodology, the business risk profile carries more weight for investment grade anchors, while the financial risk profile dominates for speculative grade anchors, which makes intuitive sense: for a highly levered borrower, the near-term question really is whether the cash flow covers the debt.

Liquidity deserves particular attention because it is the factor most likely to cause an abrupt multi-notch downgrade. A company can look acceptable on leverage and still be cut hard if a large maturity wall sits twelve months out with no committed refinancing in place.

Credit ratings show up in almost every DCM and leveraged finance interview: Work through debt, credit, and capital markets technicals with worked answers, start practicing interview questions for free and find the gaps before an interviewer does.

The rating you read in a headline is usually the issuer rating, an assessment of the borrower's overall likelihood of default. Individual bonds and loans are rated separately, because what a lender recovers after default depends entirely on where that lender sits in the capital structure.

Notching

Adjusting the rating of a specific debt instrument above or below the issuer's rating to reflect differences in expected recovery. Secured obligations, which have first claim on collateral, are typically notched up; subordinated and structurally subordinated obligations are typically notched down. Notching separates probability of default (identical for all instruments of one borrower) from loss given default (very different across the stack).

Secured, Unsecured and Subordinated

Probability of default is a property of the borrower: if the company files, everything in the capital structure is in default simultaneously. Loss severity is a property of the instrument. Moody's recovery research has long shown that senior secured debt loses dramatically less than senior unsecured debt in the same default, while subordinated debt of the same issuer loses substantially more than the senior unsecured layer.

That translates into practice roughly as follows:

Notching also compresses as credit quality falls. For a strong investment grade issuer, default is remote enough that recovery differences barely matter, so the whole stack tends to cluster near the issuer rating. For a CCC issuer, where default is a live scenario, the gap between first lien and unsecured paper can be several notches wide.

Structural Subordination

Contractual subordination is written into documents. Structural subordination is created by the corporate chart, and it is the version candidates most often miss.

Structural Subordination

The disadvantage suffered by creditors of a holding company relative to creditors of its operating subsidiaries. Because subsidiary lenders have a direct claim on the assets and cash flows that generate value, they are paid in full before anything flows up to the parent as residual equity value. Holdco debt is therefore rated below opco debt of the same group even when no document says it is subordinated.

This is why sponsors issue holdco PIK notes at the top of a structure and why an upstream guarantee from operating subsidiaries is one of the most valuable things a bondholder can negotiate: the guarantee moves the claim down to where the assets actually are. The interaction between guarantees, security packages, and permitted transfers of assets away from lenders is heavily contested in documentation, and our explainer on maintenance versus incurrence covenants covers the provisions that police it.

Agencies rarely surprise the market with a rating change out of nowhere. They telegraph, and the vocabulary of that telegraphing is worth knowing precisely.

An outlook is the agency's view of the likely direction of a rating over a medium horizon, and it changes far more often than the rating itself. A watch or review is a much sharper signal: the agency has identified a specific event and expects to resolve it quickly.

Rating Outlook

An agency's assessment of the likely direction of a credit rating over the medium term, published as positive, stable, negative, or developing. An outlook is not a commitment to act; it indicates the direction of pressure. It differs from a CreditWatch or review, which signals a specific pending event and a decision expected within roughly ninety days.

The terminology differs by agency, which matters if you are asked to read a rating action. S&P places issuers on CreditWatch positive, negative, or developing, and states that a CreditWatch generally resolves within about ninety days. Moody's places issuers on review for upgrade or downgrade. Fitch uses Rating Watch Positive, Negative, or Evolving. An issuer on watch typically does not carry an outlook at the same time, because the watch supersedes it.

How a Downgrade Transmits into Pricing and Documents

A downgrade hits a borrower through several channels at once, and being able to list them cleanly is a strong interview answer.

The most consequential ratings event in the corporate market is a crossing of the investment grade line. A downgrade from investment grade into high yield creates a fallen angel; an upgrade in the other direction creates a rising star.

The reason these events produce outsized price moves is mechanical rather than analytical. A bond that fails the index rating test is removed from the investment grade benchmark at the next rebalance and added to the high yield benchmark. Every fund tracking the investment grade index must sell it regardless of what its own analysts think, and every high yield tracker must buy it. A large fallen angel can also distort the index it enters, because the high yield market is much smaller than the investment grade market: two sizeable names joining at once can visibly shift the benchmark's sector and duration profile.

That forced flow frequently overshoots. Selling pressure driven by mandate rather than by fundamental view pushes the bond below where its credit risk alone would justify, which is why dedicated fallen angel strategies exist and why the trade has historically been attractive in the months after a downgrade.

The Round Trip in Practice

Fallen angels are a recurring feature, not a rare event. Across 2025 there were roughly ten fallen angels against seven rising stars, and in the first quarter of 2026 a small number of large names, Paramount Skydance (cut to junk after agreeing to buy Warner Bros. Discovery) and FS KKR, crossed into high yield and between them made up more than 15% of the market value of the ICE BofA US Fallen Angel index. J.P. Morgan's early-2026 estimate put potential fallen angel volume for the year near $84 billion, though most of that figure rested on two possible downgrades rather than on broad-based deterioration, and one of them has since crossed. Treat estimates of this kind as scale, not as a number to quote.

Round trips happen too. Ford was cut to junk in 2020 as the pandemic hit auto demand, becoming one of the largest fallen angels on record, then regained investment grade in 2023 once its balance sheet and earnings recovered. A single issuer can therefore move across the line twice within a few years, and credit investors who anticipate the migration in either direction capture most of the spread move.

Ratings are commissioned, not volunteered. Understanding who writes the cheque explains most of the criticism the industry attracts.

The Issuer-Pays Model

Under the issuer-pays model, the company raising capital selects and pays the agencies that will rate its debt, typically as a fee tied to the size of the issue plus an annual surveillance fee. The model replaced a subscriber-pays arrangement in the 1970s, largely because photocopying made it impossible to sell ratings to investors without them being freely redistributed.

The conflict is obvious once stated: the entity being judged chooses the judge and pays the fee. That creates an incentive for agencies to compete on outcome rather than on quality, a dynamic known as ratings shopping, where an issuer solicits preliminary feedback from several agencies and only commissions the ones offering the most favorable view.

The Critique and What Changed After 2008

The critique moved from academic to systemic in 2008, when structured finance products carrying top ratings suffered losses that no AAA population should have produced. The regulatory response in the United States, delivered through the Credit Rating Agency Reform Act and later the Dodd-Frank Act, brought agencies under direct oversight as Nationally Recognized Statistical Rating Organizations and created a dedicated SEC Office of Credit Ratings that examines each of them annually and publishes findings on competition, transparency, and conflicts of interest. The SEC's annual staff report on rating agencies is the primary public document on how those conflicts are managed, and the register of firms authorised as NRSROs shows how concentrated the industry remains despite a decade of encouragement for competitors.

Structural fixes have been partial. Analyst compensation is now walled off from fee negotiation, rating committees are documented, and methodologies are published in full. What has not changed is the payment direction, and the concentration of the market in three firms means an issuer that dislikes an outcome has limited alternatives that the market will accept. Being able to state the critique fairly, and to note both what regulation fixed and what it did not, is the sort of nuance that stands out in a credit interview.

Ratings questions are popular precisely because they connect analysis, documentation, and market structure in one answer. A candidate who can move across all three sounds like someone who has seen a deal.

The strongest answers treat a rating as a piece of market infrastructure rather than as a score. Ratings determine index membership, index membership determines forced flow, forced flow determines the technical component of spread, and spread determines what the client pays. A DCM analyst thinks about ratings in terms of which investor pool a deal can reach; a leveraged finance analyst thinks about them in terms of how many turns of leverage the structure supports and where the notching lands on each tranche. Speaking in either of those registers is more convincing than reciting the scale.

Questions You Should Expect

If you are aiming at a capital markets seat specifically, it helps to understand where ratings sit within the wider financing product set, which our comparison of equity capital markets and debt capital markets lays out.

Ratings sit at the center of the debt technicals: Download our comprehensive 160-page PDF, access the IB Interview Guide covering credit analysis, debt structures, and capital markets questions in depth.

Credit ratings are best understood as the market's shared shorthand rather than as an oracle. The letters themselves are opinions, and reasonable analysts disagree about them all the time, which is why split ratings exist and why credit funds employ people to argue with the agencies for a living. What makes ratings powerful is not their accuracy but their institutional weight: they are wired into regulation, into mandates, into indices, and into the documents that govern billions of dollars of debt, so a change in the letter forces real money to move whether or not anyone believes it. Learn the scales, learn the analysis behind them, and learn the plumbing that turns a notch into a trade, and the ratings questions in a DCM, leveraged finance, or credit interview stop being memorisation and start being a conversation about how the market actually works.