What credit spreads are
A credit spread is the yield premium a corporate bond pays above the equivalent-maturity Treasury bond. It compensates investors for credit risk — the possibility that the corporate borrower defaults. The higher the credit risk, the wider the spread.
Investment-grade corporate spreads (IG spreads) are typically measured in basis points (1bp = 0.01%). In benign environments, IG spreads might be 80-100bp. In severe stress (2008, March 2020), they can reach 300-400bp. High-yield (HY) spreads are much wider — 300-400bp in calm markets, 800-1000bp+ in crises.
Spread widening means corporate bonds are underperforming Treasuries — the market is pricing in more credit risk. Spread tightening means corporate bonds are outperforming — risk appetite is healthy. You can follow this through the HYG (high yield) and LQD (investment grade) ETFs.
Credit spreads are arguably the most reliable leading indicator for equity markets. High-yield spreads typically begin widening 2-4 weeks before equity indices crack significantly. Monitoring HYG/LQD ratio or following dedicated credit spread charts gives equity traders advance warning.
How spreads affect markets
Widening spreads tighten financial conditions — companies face higher borrowing costs, making investment and acquisition more expensive. Highly leveraged companies (private equity-backed, LBO candidates, junk-rated issuers) are hit hardest. Their stock prices often underperform significantly during spread-widening episodes.
Narrowing spreads ease financial conditions. Capital flows freely, leveraged deals are cheap to finance, and companies with balance sheet stress can refinance at lower rates. Risk assets broadly benefit from spread compression — it's the same dynamic as risk-on, which it partially causes.
The correlation between HYG (high-yield bond ETF) and SPY (S&P 500 ETF) is typically above 0.8 over rolling 3-month periods. Divergences between them are information — when HYG falls but SPY holds, credit is warning equities. When SPY falls but HYG holds, the equity move may be shallow or a buying opportunity.
Trading credit signals
The simplest practical approach: track the HYG to SHY ratio (high-yield to short-duration safe bonds). When this ratio is trending up, credit appetite is healthy and equity longs have wind. When it trends down, credit is deteriorating and equity positions need tighter risk management.
Watch for divergences at market turning points. A multi-week divergence where equities make new highs but HYG lags significantly is a warning that the equity rally may not be sustainable. The credit market, with its institutional participation and fundamental anchoring, often sees trouble before equity momentum breaks.
Credit default swaps (CDS) are the purest form of credit risk pricing — but require institutional access. The CDX.NA.IG and CDX.NA.HY indices (which track baskets of CDS) are the institutional benchmarks that equity traders can reference through media coverage when credit stress events occur.