Credit Spreads: Investment Grade vs High Yield

Key Takeaways

• IG OAS historically ranges 80–200 bps; HY OAS ranges 300–500 bps in calm markets and exceeded 1,000 bps in the 2008 crisis and briefly in March 2020.
• Option-adjusted spread (OAS) strips out embedded call options to give a purer credit-risk reading than the simpler Z-spread or G-spread.
• HY is typically 3–6x more volatile than IG and reacts earlier to growth scares; IG widening while HY barely moves usually signals a rates story, not a credit story.
• A handful of deeply distressed CCC-rated names can drag the whole HY index wider even when BB credits are fine, always check the sub-index composition.

What It Is

The spread is a simple subtraction. You take the yield on a corporate bond and subtract the yield on a matched-maturity Treasury. What remains is compensation for credit risk, liquidity, and optionality that the Treasury does not carry.

Two buckets matter most. Investment grade (IG) covers issuers rated BBB minus and above by S&P or Baa3 and above by Moody's. High yield (HY), also called junk or speculative grade, covers BB plus and below. The usual benchmarks are the ICE BofA US Corporate Index for IG and the ICE BofA US High Yield Index for HY, both published on FRED as option-adjusted spreads.

The Intuition

Treasuries are priced as if the US government will pay. Corporate bonds are not. Investors demand a cushion for the chance of default, the odds of recovery if default happens, and the fact that corporate bonds are harder to sell in a panic. The spread is that cushion, expressed in basis points.

Because the spread updates every day and aggregates hundreds of issuers, it reacts to credit conditions faster than earnings reports or default statistics. When spreads widen, the bond market is pricing in rising default probability. When they tighten, lenders are competing to finance weaker borrowers, which usually means late-cycle confidence.

How It Works

The cleanest version of the spread is the option-adjusted spread (OAS). A naive Z-spread just measures the extra yield at a single point on the Treasury curve. OAS strips out the value of embedded optionality, such as a call feature that lets the issuer refinance cheaply if rates fall. After stripping that option value, OAS gives a purer read on credit risk.

corporate yield = Treasury yield + OAS
OAS approximates: default risk + liquidity premium + residual compensation

Typical ranges give you a sense of scale. IG OAS historically runs between roughly 80 and 200 basis points, tightening below 90 bps in calm periods like 2021 and widening past 600 bps in the worst weeks of the 2008 crisis. HY OAS is far more cyclical, with a normal band of 300 to 500 bps, stress readings above 700 bps, and crisis blowouts above 1,000 bps in 2008 and briefly in March 2020.

Practitioners watch the level, the rate of change, and the gap between IG and HY. A sudden 100 bps widening in HY while IG barely moves tells you the market is repricing the weakest borrowers specifically, not the whole curve.

Worked Example

Assume a 10-year Treasury yields 4.2 percent. A BBB-rated industrial bond with 10 years to maturity and comparable duration yields 5.5 percent. The spread is 5.5 minus 4.2, which equals 1.3 percent, or 130 basis points. That sits squarely inside the historical IG range.

Now suppose a BB-rated issuer with similar maturity yields 9.0 percent. The HY spread is 480 basis points. A month later both yields move: Treasury to 3.9 percent, the HY bond to 10.5 percent. The spread widened from 480 to 660 bps even though rates fell, a classic risk-off pattern where Treasuries rally and HY sells off simultaneously.

Common Mistakes

1. Comparing absolute spread levels across cycles without context. A 400 bps HY spread in 2007 meant something different than 400 bps in 2020. Always look at the spread relative to its recent distribution and to the level of Treasury yields, not as an absolute pass or fail.

2. Treating every spread widening as a credit event. Duration effects, liquidity squeezes, and forced selling from fund flows can widen OAS without any change in default expectations. Separating credit from non-credit drivers often requires watching CDS indices alongside cash bond spreads.

3. Conflating OAS with Z-spread or G-spread. They are close for bullet bonds with no embedded options but can diverge meaningfully for callable issues. When you compare spreads across series, make sure you are comparing the same definition.

4. Ignoring distressed-bucket composition in HY. A handful of deeply distressed names trading at 50 cents on the dollar can drag the whole index wider even when BB-rated credits are fine. The CCC sub-index tells you how much of the move is in the weakest tier.

5. Assuming IG and HY tell the same story. HY is typically 3 to 6 times more volatile than IG and reacts earlier to growth scares. When IG widens while HY barely moves, the signal is often about rates rather than credit.

Frequently Asked Questions

What is a credit spread? A credit spread is the yield a corporate bond pays above a matched-maturity Treasury, expressed in basis points. It compensates investors for default risk, liquidity, and any embedded optionality the Treasury lacks. When spreads widen, the market is pricing higher default probability; when they tighten, lenders are competing for weaker borrowers, usually a late-cycle sign.

What is the difference between investment grade and high yield spreads? Investment grade covers issuers rated BBB− and above; high yield covers BB+ and below. IG OAS historically runs 80–200 bps; HY OAS runs 300–500 bps in calm periods. HY is 3–6 times more volatile than IG and reacts earlier to growth scares. When IG widens without HY, the move usually reflects rate or duration concerns, not credit stress.

What is option-adjusted spread (OAS)? OAS strips out the value of embedded optionality, such as a call feature that lets the issuer refinance cheaply if rates fall, from the raw yield spread. This gives a purer read on credit risk. For plain-vanilla bullet bonds with no embedded options, OAS and Z-spread are nearly identical. For callable bonds, they can diverge significantly.

How do credit spreads behave in a risk-off episode? Treasuries typically rally (yields fall) while corporate bonds sell off, especially high yield. That combination widens OAS even when absolute Treasury yields are falling. A move from HY OAS of 480 bps to 660 bps while Treasuries rally is a classic risk-off pattern and is a more reliable stress signal than absolute yield levels.

Why does the HY CCC sub-index matter separately? A handful of deeply distressed names trading at steep discounts can drag the whole HY index OAS wider even when BB-rated credits are fine. When headline HY OAS spikes, checking the CCC sub-index tells you whether the widening is systemic (BB and B names moving too) or concentrated in the weakest tier of borrowers.

Sources

1. Federal Reserve Bank of St. Louis. "ICE BofA US High Yield Index Option-Adjusted Spread (BAMLH0A0HYM2)." https://fred.stlouisfed.org/series/BAMLH0A0HYM2
2. Federal Reserve Bank of St. Louis. "ICE BofA US Corporate Index Option-Adjusted Spread (BAMLC0A0CM)." https://fred.stlouisfed.org/series/BAMLC0A0CM
3. Charles Schwab. "Credit Spreads: Under the Radar, but Influential." https://www.schwab.com/learn/story/credit-spreads-under-radar-but-influential
4. Federal Reserve Bank of St. Louis. "ICE BofA BBB US Corporate Index Option-Adjusted Spread (BAMLC0A4CBBB)." https://fred.stlouisfed.org/series/BAMLC0A4CBBB

Disclaimer

This article is educational content only and is not financial advice. Nothing here is a recommendation to buy, sell, or hold any security. Consult a licensed advisor before making investment decisions.