When a company borrows money by issuing a bond, it promises to pay interest and return the principal at maturity. What rate does it pay? That depends almost entirely on one thing: creditworthiness — how likely it is to make every payment on time. Credit rating agencies translate that likelihood into letter grades, and the market translates those grades into yields. The gap between a high-grade corporate bond yield and the equivalent Treasury yield is called the spread, and it is one of the most closely watched thermometers in global finance.
This explainer covers how credit ratings work, what separates investment grade from high yield (“junk”), how spreads behave through the cycle, and what all of it means for investors and companies alike.
The Credit Rating Scale
Three agencies dominate corporate credit ratings: S&P Global Ratings, Moody’s Investors Service, and Fitch Ratings. Each uses a slightly different notation, but the logic is identical — a letter grade that signals the probability of default.
| S&P / Fitch | Moody’s | Category | Spread (bps)* | Indicative Yield* |
|---|---|---|---|---|
| AAA | Aaa | Investment grade — highest quality | 40 | 4.75% |
| AA | Aa | Investment grade — very strong | 55 | 4.90% |
| A | A | Investment grade — strong | 78 | 5.13% |
| BBB | Baa | Investment grade — lowest tier | 111 | 5.46% |
| BB | Ba | High yield — speculative grade entry | 184 | 6.19% |
| B | B | High yield — speculative | 321 | 7.56% |
| CCC | Caa | High yield — highly speculative | 885 | 13.20% |
| CC / C | Ca / C | High yield — near or in default | 1,261–1,900 | 17%+ |
Indicative yields = 10-year Treasury (4.354%, Yahoo Finance April 28, 2026) + spread. The double line marks the IG/HY boundary.
The boundary between investment grade (IG) and high yield (HY) sits between BBB/Baa and BB/Ba. It is not just a label — it has enormous practical consequences. Most insurance companies, pension funds, and money-market funds are legally restricted to holding only investment-grade securities. When a company falls from BBB to BB — a so-called fallen angel — forced selling by index funds and institutional mandates can push its bond prices sharply lower even before default risk meaningfully changes.
What the Spread Actually Tells You
Think of the spread as the extra interest rate a company must pay over a “risk-free” government bond to compensate investors for the chance it might default. A 184 bps spread on a BB bond means the issuer is paying roughly 1.84 percentage points more per year than the US Treasury for money with the same maturity.
The spread encodes three things at once:
- Default risk premium — compensation for the probability of non-payment
- Recovery rate assumption — if default happens, investors historically recover about 40–50 cents on the dollar for senior secured bonds, less for subordinated debt
- Liquidity premium — corporate bonds trade less freely than Treasuries; investors demand extra yield for that illiquidity
In practice, spreads tighten when investors are confident (risk-on) and widen when they are fearful (risk-off). The high-yield spread is often called a “fear gauge” for credit markets — similar to how the VIX measures equity fear.
Why Spreads Blow Out in Downturns
In a recession or financial crisis, two things happen simultaneously: the probability of corporate defaults rises, and investors rush toward safety. Both forces push HY bond prices down and spreads wider. During the 2008 global financial crisis, the ICE BofA US High Yield spread peaked at nearly 2,000 basis points — meaning junk bonds yielded 20 percentage points more than Treasuries. During the March 2020 COVID shock, spreads hit roughly 1,100 bps before the Federal Reserve’s intervention stabilized markets. As of late April 2026, the index spread sits at approximately 350 bps — below its long-run average and consistent with a market pricing modest default risk.
Default Rates: What the History Shows
Rating grades are calibrated to historical default outcomes. Based on Moody’s long-run average default studies (published annually since the 1980s), the pattern is stark:
- Investment-grade bonds (AAA through BBB): average 1-year default rates below 0.3%. Even over a 5-year horizon, cumulative default rates for IG bonds have historically remained below 2%.
- BB-rated bonds: roughly 1–2% annual default rate. Risky, but many BB issuers are profitable companies with manageable leverage — they simply haven’t qualified for IG status.
- B-rated bonds: roughly 3–5% annual default rate. These issuers carry meaningful leverage and depend on stable operating conditions.
- CCC-rated bonds: roughly 10–15% annual default rate. Default is a real near-term possibility; the spread is compensation for that risk.
The key insight: higher yield is not “free money.” It is compensation for taking on a measurably higher chance of losing principal. Whether that trade-off is worth it depends on the spread relative to expected losses — a calculation professional credit analysts make with models, not intuition.
The Fallen Angel and the Rising Star
Rating changes have outsized market impact because of institutional mandates. Two terms matter:
- Fallen angel — a bond that was investment grade and gets downgraded to high yield. The forced selling from IG-only funds can push prices down 5–15% in days, even if the company’s business hasn’t materially deteriorated. Famous fallen angels include Ford, Delta Air Lines, and Kraft Heinz, all of which lost IG status during different stress cycles.
- Rising star — a high-yield bond upgraded to investment grade. This triggers buying from IG funds, often producing quick price gains. Rising-star upgrades were common in 2021 as companies recovered from COVID cash burns.
Investment Grade vs High Yield: Who Issues Each
The typical IG issuer is a large, established company with diversified revenue, modest leverage (net debt/EBITDA below 3×), and predictable cash flows — think Microsoft, Apple, Johnson & Johnson, or Walmart. Major banks, utilities, and sovereign governments dominate the IG market.
HY issuers are often smaller, more leveraged, or operating in cyclical industries. Private equity-backed companies — taken private in leveraged buyouts — make up a large slice of the HY universe, since the buyout itself loads the company with debt that pushes it below IG. Airlines, energy producers, cable companies, and retailers are also frequent HY issuers. The HY market is not just “bad companies” — it includes plenty of profitable businesses that have temporarily higher leverage or have yet to build the track record that earns an IG rating.
How to Track Spreads Yourself
The most widely followed benchmarks are published daily by ICE (formerly BofA Merrill Lynch) and available for free on the St. Louis Federal Reserve’s FRED database:
- BAMLH0A0HYM2 — ICE BofA US High Yield OAS (the primary HY spread gauge)
- BAMLC0A0CM — ICE BofA US Corporate (IG) OAS
- BAMLH0A2HYM2BB — BB-only segment, useful for tracking the HY/IG borderline
When HY spreads are widening while equity markets are calm, it can be an early warning signal that credit markets are detecting stress before it shows up in stock prices. The reverse — tight HY spreads alongside rising equities — tends to signal a risk-on regime where capital is freely available.
Common Misconceptions
“Junk bonds are always bad investments.” Not true. Across many historical periods, HY bonds have outperformed IG bonds on a total return basis because the extra yield more than offset the extra defaults. The key is diversification — holding a portfolio of 50+ HY bonds so that a few individual defaults don’t wipe out the income from the rest.
“AAA means no risk.” AAA means very low default risk — not zero. AAA-rated mortgage securities failed catastrophically in 2008 because their models underestimated correlated defaults across housing markets. The rating reflects the agency’s model, not a guarantee.
“The spread is the whole story.” Spreads are quoted as option-adjusted (OAS), meaning they strip out the effect of embedded call or put options. A raw yield comparison can be misleading if one bond is callable and another isn’t.
What to Learn Next
- Leveraged buyouts (LBOs) — why PE firms issue HY debt to fund acquisitions
- CLOs (Collateralized Loan Obligations) — how bank loans get tranched into rated securities
- Duration and convexity — how to measure a bond’s sensitivity to interest-rate changes
- Private credit — direct lending as an alternative to the public HY bond market
- Credit default swaps (CDS) — the derivative market where default risk is bought and sold
Sources
- Aswath Damodaran, NYU Stern School of Business — Default Spreads by Rating, January 2026.
- Yahoo Finance — US Treasury Yields, April 28, 2026 (10-year: 4.354%, 30-year: 4.944%).
- Federal Reserve Bank of St. Louis (FRED) — ICE BofA US High Yield Option-Adjusted Spread: series BAMLH0A0HYM2.
- Federal Reserve Bank of St. Louis (FRED) — ICE BofA US Corporate OAS: series BAMLC0A0CM.
- Moody’s Investors Service, Annual Default Study: Corporate Default and Recovery Rates (published annually; historical default-rate averages by rating category).
- S&P Global Ratings — credit rating scale and definitions.
Disclosure: This article was produced with AI assistance and reviewed before publication. It is for informational purposes only and is not investment advice.