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Credit Rating

A credit rating is an assessment of a bond issuer’s ability and willingness to meet its debt obligations. Ratings agencies (Moody’s, S&P, Fitch) assign letter grades: AAA/Aaa (highest quality), through BBB/Baa (investment-grade), to BB/Ba and below (speculative-grade), down to D (default). Ratings determine borrowing costs, market access, and investor eligibility.

For investment-grade ratings, see investment-grade bond. For speculative-grade ratings, see high-yield bond and junk bond.

The rating scale

Moody’s scale:

  • Aaa, Aa1, Aa2, Aa3 (highest investment-grade)
  • A1, A2, A3
  • Baa1, Baa2, Baa3 (lowest investment-grade)
  • Ba1, Ba2, Ba3 (highest speculative)
  • B1, B2, B3
  • Caa–C (lowest speculative)
  • D (default)

S&P and Fitch scale:

  • AAA, AA+, AA, AA- (highest investment-grade)
  • A+, A, A-
  • BBB+, BBB, BBB- (lowest investment-grade)
  • BB+, BB, BB- (highest speculative)
  • B+, B, B-
  • CCC, CC, C (lowest speculative)
  • D (default)

The scales are similar; Moody’s uses decimal modifiers (Baa1, Baa2, Baa3) while S&P/Fitch use plus/minus.

What ratings measure

Ratings assess:

  1. Ability to repay — Does the company have sufficient cash flow, assets, and financial flexibility to meet obligations?
  2. Willingness to repay — Does the company prioritize debt service? Are there governance concerns?
  3. Economic environment — Are industry conditions favorable or distressed?
  4. Capital structure — Is debt reasonable relative to equity and cash flows?

Ratings are forward-looking — they assess future repayment probability, not just current financial health.

Rating actions and outlooks

When a company’s credit profile changes, ratings agencies issue rating actions:

  • Upgrade — Rating improves (e.g., Ba1 to Baa3)
  • Downgrade — Rating worsens (e.g., Baa2 to Ba1)
  • Affirmation — Rating unchanged but may include outlook change

An outlook signals the likely direction:

  • Positive — An upgrade is likely within 12 months
  • Negative — A downgrade is likely within 12 months
  • Stable — Unlikely to change

Market impact of ratings changes

Rating changes move bond prices:

  • Downgrade — Bond price falls as investors demand wider credit spread
  • Upgrade — Bond price rises as credit spread narrows

A downgrade from investment-grade to speculative-grade (a “fallen angel”) can cause sharp price declines because regulated investors (pension funds, insurance companies) are forced to sell.

An upgrade to investment-grade (a “rising star”) can cause significant price appreciation as institutional demand increases.

Rating bias and criticism

Rating agencies faced severe criticism post-2008. They gave AAA ratings to mortgage-backed securities and CDOs that subsequently defaulted at high rates.

Sources of bias:

  • Issuer conflicts — Agencies are paid by bond issuers (conflict of interest)
  • Complexity blindness — Complex structures (CDOs) overwhelmed analysts
  • Procyclicality — Upgrades in booms; downgrades after crisis has started
  • Statistical errors — Models assumed default correlation lower than actual

Post-crisis, regulations tightened. But structural conflicts remain, and ratings should not be the sole basis for credit decisions.

Spread and rating relationship

Credit spreads correlate with ratings:

  • AAA — 50–150 basis points
  • BBB — 250–500 basis points
  • BB — 500–1,000 basis points
  • B — 1,000–2,000 basis points

These ranges vary with economic cycle and market conditions, but the hierarchy is reliable.

Investment policy restrictions

Many investors have policies restricting holdings to investment-grade (BBB- or higher). Ratings thus determine who can hold a bond:

  • A BBB-rated bond can be held by most investors
  • A BB-rated bond cannot be held by many institutional investors
  • An unrated bond cannot be held by conservative investors

This creates cliff risk: a downgrade to BB forces institutional selling, depressing prices.

Corporate vs. sovereign ratings

Corporate ratings assess individual companies. Sovereign ratings assess countries’ abilities to repay.

A corporation can be rated higher than its sovereign (e.g., a Swiss multinational rated AAA while Switzerland is Aaa). A sovereign can be rated lower (e.g., an emerging market rated B while a stable multinational is BBB).

ESG and ratings

Ratings agencies increasingly incorporate environmental, social, and governance (ESG) factors. Severe ESG problems can lead to rating downgrades independent of financial metrics.

See also

Wider context