Credit Spreads and Ratings

A credit spread is the yield difference between a risky bond and a risk-free Treasury of the same maturity. Spreads are tightly correlated with ratings: AAA bonds trade 50–100 basis points (bps) wide; BBB bonds, 120–200 bps; BB bonds, 250–400 bps; and so forth. During calm markets, spread-rating relationships are stable and predictable; during stress, spreads widen dramatically, especially for lower-rated bonds. Mastering spread-rating dynamics enables both portfolio construction (matching yield expectations to risk tolerance) and tactical opportunity spotting (buying bonds when spreads are rich, selling when tight).

Key takeaways

• A credit spread (OAS: option-adjusted spread) is the yield premium a bondholder receives for assuming credit risk, measured in basis points above a risk-free benchmark.
• Spreads are inversely correlated with bond ratings: each notch down in rating typically adds 30–80 bps to the spread (wider at lower rating tiers).
• Spread compression (narrowing) occurs during economic expansions, falling interest rates, and periods of investor risk appetite; spread widening occurs during recessions, policy tightening, and crisis.
• A bond's total return depends on both the spread at purchase and the spread at sale (or maturity); if spreads widen, the bondholder suffers a price loss even with no credit deterioration.
• Relative value trades exploit temporary mispricing: buying bonds with spreads wider than fundamental risk warrants, or selling bonds with spreads tight relative to rating.

Spread basics: yield, maturity, and risk-free rate

A bond's yield has three components:

1. Risk-free rate: The yield on a Treasury of the same maturity. This reflects the market's expectation of future interest rates and inflation.
2. Credit spread: The additional yield for assuming default risk and liquidity risk.
3. Other adjustments: Call features, optionality, and technical supply-demand imbalances.

Example: A 7-year corporate bond yields 4.0%. The 7-year Treasury yields 2.5%. The credit spread is 4.0% − 2.5% = 150 bps.

The credit spread compensates the bondholder for:

• Default probability: Higher-rated bonds have lower default probability and therefore tighter spreads.
• Loss-given-default (recovery rate): Senior secured bonds (high recovery) trade tighter than subordinated bonds (low recovery).
• Liquidity: Less liquid bonds trade wider than more liquid bonds of the same rating.
• Option value: Callable bonds trade wider than non-callable bonds because the issuer can refinance the bond if rates fall, capping the bondholder's upside.

Spread by rating tier

Empirical data (from Bloomberg, Refinitiv, and agency reports) shows typical spreads by rating:

Rating	Typical OAS (bps)	Spread Range (bps)
AAA	50–80	30–120
AA	60–100	40–150
A	80–130	50–200
BBB	120–180	80–250
BB	250–350	180–500
B	350–500	250–800
CCC	600–1000	400–1500

These are median values during normal market conditions (2010–2021 average). During crisis periods (2008, March 2020), all spreads widen; during euphoric periods (mid-2013, late 2017), spreads tighten.

Spread-rating relationships: the notch-by-notch progression

Moving down one notch in rating typically widens spreads by:

• AAA to AA: 20–30 bps.
• AA to A: 20–40 bps.
• A to BBB: 30–50 bps.
• BBB to BB: 80–120 bps (larger jump at the IG/HY cliff).
• BB to B: 80–120 bps.
• B to CCC: 150–300 bps (larger jump at distress threshold).

The jumps are not linear because:

1. Investment-grade cliff: The BBB/BB boundary is the most significant, reflecting regulatory and indexing discontinuities.
2. Distress cliff: As bonds approach default (CCC, C), the spread widens non-linearly because recovery becomes increasingly uncertain.
3. Liquidity bias: Widely-held AAA and A bonds are very liquid, compressing spreads; illiquid CCC and C bonds trade with a liquidity premium.

Spread changes and total return

A bondholder's total return has two sources:

1. Yield/carry: The coupon and accrued interest earned over the holding period.
2. Price change: Change in the bond's value due to interest rate and spread movement.

If spreads widen (bond becomes riskier, yield rises), the price falls. If spreads tighten (bond becomes less risky, yield falls), the price rises.

Example: You buy a BBB corporate bond yielding 3.5% (150 bps OAS over 2.5% risk-free rate). You hold for one year. During that year, the risk-free rate stays at 2.5% and you collect 3.5% coupon. But the bond's credit quality deteriorates slightly, and BBB spreads widen to 200 bps. The bond now yields 4.5%. Its price has fallen; you suffer a loss despite collecting your coupon. Your total return is negative.

This illustrates why credit investors must track not just default probability but also spread moves. A AAA bond yielding 2.6% (barely above risk-free) offers little return cushion; if spreads widen even 10 bps, the price loss eats the year's carry. A BBB bond yielding 3.5% offers more cushion; a 10 bps spread widening is offset by carry.

Spread cycles and credit cycles

Spreads are highly cyclical, driven by the credit cycle:

Expansion phase: Earnings rising, defaults low, investor risk appetite high. Companies are refinancing at lower costs; credit quality is stable or improving. Spreads compress: BBB spreads might fall from 180 bps to 120 bps. Bond prices rise.

Peak phase: Interest rates rising or expected to rise. Credit quality is still solid but growth is slowing. Spreads hold steady or begin to widen slightly.

Contraction phase: Recession, earnings declining, defaults rising, risk appetite falling. Companies are struggling to refinance; credit quality deteriorating. Spreads widen dramatically: BBB spreads might jump from 180 bps to 300 bps or higher. Bond prices fall sharply.

Trough phase: Crisis peak. Spreads are at maximum; many bonds are illiquid, trading far below quoted prices. Risk-on trade: credit spreads are so wide that long-term returns are attractive, signaling opportunity for patient investors.

The credit cycle typically spans 3–5 years. Investors who can time the cycle—buying in troughs, selling before peaks—can generate substantial returns. However, timing is notoriously difficult.

Spread compression and expansion: causes

Spread compression (tightening) occurs when:

• Central banks cut interest rates or signal dovish policy.
• Economic growth accelerates.
• Corporate earnings surprise to the upside.
• Investor risk appetite rises (equities rally, VIX falls).
• Fed balance sheet expands (increases liquidity).

Spread widening (expanding) occurs when:

• Central banks raise rates or signal hawkish policy.
• Economic growth slows or recession begins.
• Corporate earnings decline or guidance is cut.
• Investor risk appetite falls (equities decline, VIX rises).
• Credit events (rating downgrade waves, major default) erode confidence.

Fallen angels and rising stars: spread repricing

A bond downgraded from BBB− to BB+ experiences double pressure:

1. Fundamental spread widening: The new BB+ rating comes with higher spreads (BBB spreads are 150–200 bps; BB spreads are 250–400 bps).
2. Mechanical selling: Index funds and policy-bound funds forced to sell the downgraded bond, depressing price further.

The net effect can be a 150–200 bps widening, translating to a 5–10% price drop on an intermediate-term bond, even with no change in interest rates.

Conversely, a rising star (bond upgraded from BB+ to BBB−) experiences:

1. Fundamental spread tightening: BBB spreads are lower than BB spreads.
2. Index buying: Index funds must buy the upgraded bond to remain index-compliant, supporting price.

The net effect can be a 100–150 bps tightening, translating to a 3–8% price gain.

Relative value: exploiting spread mispricings

Active managers and traders exploit temporary mispricing of credit spreads:

• Sector trades: If energy spreads have widened to 300 bps while technology spreads remain at 200 bps (both sectors rated BB), a manager might short energy and long technology, betting that energy spreads compress as commodity prices recover.

• Rating-relative trades: If all BBB bonds have widened to 200 bps but one BBB issuer (with strong fundamentals) has widened to 250 bps due to temporary negative news, a manager might buy that issuer's bond, betting spreads retighten.

• New-issue premium: Newly issued bonds sometimes offer higher spreads than secondary market bonds of the same rating/maturity (liquidity premium for new issue). A manager might buy new issues, wait for the secondary bid to arrive, and realize a quick capital gain.

Curve positioning and spread duration

Bond portfolio managers manage "spread duration"—sensitivity to spread changes. A portfolio positioned for spread compression (by buying bonds with wider spreads) will outperform if spreads compress but will underperform if spreads widen.

Example: You build a portfolio of BBB bonds yielding 3.5% (200 bps OAS). The neutral expectation is BBB spreads at 150 bps, which would yield 3.0%. Your portfolio is paying extra because spreads are currently wide. If spreads compress to 150 bps, you will have a capital gain. If spreads widen to 250 bps, you will have a capital loss.

Managing spread exposure is distinct from managing interest rate risk (duration) and is a key source of alpha (outperformance) in credit investing.

Spread volatility and risk metrics

Rating agencies and credit indices publish:

• Average OAS by rating: A trailing 12-month average, showing typical spreads by rating during normal conditions.
• Spread dispersion: The standard deviation of spreads within a rating, showing outliers (some bonds trade wider or tighter than peers).
• Spread vol: The historical volatility of spread changes, showing how unstable spreads are (useful for hedging and option pricing).

Higher spread volatility makes spread timing riskier; wider spreads create more opportunity but also more downside risk if spreads widen further.

Flowchart

Related concepts

• Rating Scales Explained
• The Investment-Grade vs Junk Line

Next

The final article in this chapter examines how rating changes translate into price moves and the interplay of fundamental deterioration, spread widening, and mechanical forced selling that compounds losses on downgrades.