Three firms grade the debt of governments and companies: Moody's, S&P, and Fitch.

Their grades shape how much borrowers pay and what big funds are allowed to hold.

In May 2025, the last perfect grade on U.S. debt fell, so the machine is worth opening up.

On May 16, 2025, Moody's cut the U.S. from Aaa to Aa1, its top notch to the next one down.

Moody's was the last major agency to hold the U.S. at the top, a status it had kept since 1917.

S&P cut the U.S. in 2011, and Fitch cut it in 2023.

Moody's pointed to rising debt and repeated failures to control it.

It projected federal debt near 134% of GDP by 2035, up from about 98% in 2024.

A rating is an opinion on the odds of being paid back in full and on time.

Analysts weigh debt levels, income, growth, and the will to pay.

The grade runs from AAA at the top down through investment grade to junk.

The grade matters because rules and funds are wired to it.

Some funds may only hold investment-grade debt, so a cut can force selling.

For the U.S., though, Treasuries are exempt from many of those rules, so forced selling is limited.

The first stress point is a cliff. A cut from investment grade to junk can trigger forced selling all at once.

That risk is real for companies and weaker countries, less so for the U.S.

The second is confidence. A downgrade is a signal, even when no rule forces a trade.

The third is timing. Agencies often move late, after the market already knows.

The 2011 and 2023 U.S. cuts drew headlines but no lasting jump in borrowing costs.

The rating system gives a common language for risk across thousands of borrowers, and that is useful.

For the U.S., the grade is a comment, not a constraint. The dollar and Treasury market run on more than a letter.

What can break for others is the cliff, when a cut forces funds to dump bonds into a falling market.

You can watch the agencies' own actions. Each posts its ratings and outlook changes publicly.

The 10-year Treasury yield shows whether markets actually demand more to lend.

A credit rating is a graded opinion wired into rules and funds, and for most borrowers it bites.

For the U.S., the Moody's cut is a warning label, not a forced sale.

The next test is whether debt keeps climbing toward the 134% path Moody's flagged. Watch the 10-year yield and future agency outlooks.