Moody's took away America's last AAA rating — so why didn't Treasury yields care?

On May 16, 2025, the United States lost the last perfect credit rating it had. Moody's cut the federal government from Aaa to Aa1, the top grade it had assigned the country since 1917. S&P had already moved in 2011 and Fitch in 2023, so Moody's was the final holdout. After more than a century, no major agency rates U.S. debt at the very top anymore.

A downgrade of the world's benchmark borrower sounds like it should have jolted the bond market. It didn't. The 10-year Treasury yield ticked up about two basis points at the Monday open, to roughly 4.46%, and then investors spent the session buying, pulling yields back down from the highs. The reaction was muted.

Stranger still is the precedent. When S&P first downgraded the U.S. in August 2011, the stock market fell almost 7% in a day and Treasuries rallied. The 10-year yield dropped by roughly 50 basis points as money fled into the very bonds that had just been marked down. Investors answered a downgrade by buying more of the asset that was downgraded.

That gap between what a rating agency says and what the market actually charges is the heart of how CFA Level I treats credit risk.

Credit risk has three parts

The curriculum splits credit risk into distinct pieces, and the downgrade story separates them cleanly.

• Default risk is the chance the issuer misses a contractual payment. For a government that borrows in a currency it prints, this is close to zero, because it can always create the dollars to pay. That is why Treasuries are the textbook "risk-free" asset.
• Downgrade risk is the chance the rating itself falls. That is exactly what happened in 2025. A downgrade usually widens spreads on the spot, because lower-rated paper trades cheaper, and some institutions are mandated to sell once a bond slips below a threshold.
• Spread risk is the chance the yield premium widens even when nobody defaults. For investment-grade bonds, this mark-to-market move is the dominant source of credit-related volatility.

The 2025 episode was a downgrade with almost no default-risk content. Moody's was not predicting a missed payment. It was flagging the trajectory: persistent deficits, a rising interest bill, and federal debt it projected could near 134% of GDP by 2035, up from about 98% in 2024.

What a rating actually measures

A rating is an agency's opinion about the probability of default, not a real-time, market-based price. Rating changes typically lag the market: by the time Moody's acted, the concerns it cited had been public for years, and Treasury yields already reflected them.

That is why the standard analytical move is to compare a bond's actual yield spread to the spread its rating would imply. When the two disagree, the agency is often the one behind. In 2011 the market's verdict was the opposite of S&P's: faced with global stress, investors decided U.S. government debt was the safest place to be, downgrade or not.

The core credit math shows why a government bond is a special case:

For a corporate bond with a 3% annual default probability and a 60% recovery rate, expected loss is 0.03 × 0.40 = 1.2% of face value a year, a real cost the spread has to cover. For a Treasury, the default-probability term is effectively zero, so the expected loss is too. The yield it pays is not compensation for default; it is term premium, liquidity, and the market's shifting view of supply and inflation, none of which a single rating notch captures.

The lesson the downgrade teaches

The "risk-free rate" is a modeling convention, and a credit rating is one opinion among many, usually a late one. The market prices credit continuously through spreads, while agencies re-grade it only occasionally. When the two diverge, an analyst's job is to ask which is right, not to assume it is the agency.

For the exam, the takeaways are the ones the curriculum rewards: keep default risk, downgrade risk, and spread risk separate; remember that investment grade ends at Baa3/BBB−; and know that the biggest price move from a downgrade often comes not from higher default odds but from forced selling and a wider spread. A country can lose its last top rating and still borrow more cheaply than most of the firms that were never downgraded at all.