The rating scale, from AAA to default
| S&P / Fitch | Moody's | Category | What it signals |
|---|---|---|---|
| AAA | Aaa | Investment grade | Highest quality. Very low default risk. US Treasuries sit here (or near it). |
| AA | Aa | Investment grade | Very strong issuers. Top-tier corporates and most large governments. |
| A | A | Investment grade | Strong but somewhat more sensitive to adverse conditions. |
| BBB | Baa | Investment grade (lowest tier) | Adequate capacity. The crucial boundary — one notch above 'junk.' |
| BB / B / CCC | Ba / B / Caa | High yield (junk) | Speculative. Higher coupons compensate for materially higher default odds. |
| D | D | Default | Payment missed or bankruptcy filed. Recovery depends on the capital structure. |
The BBB/BB downgrade cliff
Many large institutional pools of capital — pension funds, insurance company general accounts, certain mutual funds — are restricted by mandate to investment-grade bonds only. When a bond gets downgraded from BBB to BB, it is not just a notch lower on a spectrum; it crosses a wall. Those forced holders must sell whether they want to or not, and the new buyers (high-yield specialists) typically pay less. The price drop tied to a BBB-to-BB downgrade is often much larger than the credit-quality change alone would justify, because the seller pool and buyer pool are completely different ecosystems.
How a downgrade unfolds, step by step
1. Watch list. Before any actual rating change, the agency announces 'negative watch' or 'positive watch' — they are reviewing and a move is plausible within ~90 days. This is the earliest public warning.
2. Outlook revision. A change from 'stable' to 'negative outlook' (or vice versa) is a softer, longer-horizon signal — a downgrade is possible within 12-24 months but not imminent.
3. Actual rating action. The agency moves the rating up or down a notch (e.g., BBB to BBB-). Bond prices typically have already moved in anticipation; the actual rating change often produces a smaller reaction than the original watch placement.
4. Crossing the IG/HY line. When a downgrade pushes a bond from BBB- to BB+, it becomes a 'fallen angel.' Forced selling from investment-grade-only mandates kicks in. A reverse-direction crossing (BB+ to BBB-) is a 'rising star' and triggers forced buying from those same mandates.
Why ratings lag the market
Rating agencies are reactive by design. They review on a quarterly or semi-annual cadence, weigh several quarters of audited financials, and have to defend their conclusions in writing. The bond market trades continuously and prices in any whiff of stress immediately. Spreads almost always widen before a downgrade and tighten before an upgrade. By the time the rating agency publishes the change, professional bond investors have already repositioned. This is why 'spread first, rating later' is a saying in credit markets — and why credit spreads are widely treated as a more current signal than ratings themselves.
Compare a bond's rating to its spread
Positioning around the investment-grade boundary
Sit with the ideas.
Riverbend Power is currently rated BBB- (the lowest investment-grade notch). It has been placed on negative watch by S&P after a weak quarter. Three weeks later, S&P downgrades it to BB+, making it a 'fallen angel.' The bond's price has already fallen 8% during the three weeks before the downgrade was announced. Which statement is most accurate?