Credit ratings and AAA bonds: How a letter grade sets the price of borrowing

A credit rating is a letter grade that an outside agency gives a borrower to show how likely it is to repay its debt. AAA is the highest grade. Bonds rated BBB- or higher are called investment grade, and the grade strongly influences how much interest a borrower must pay.

The idea has moved into AI coverage because building data centers now takes more money than many companies earn in a year.

A bond is an IOU, and the grade is a reference check

Think of lending money to a neighbor. You would ask for little in return from a neighbor with a steady job and no debts. For one with a shaky record, you would want a higher payment, or you would say no.

A bond works the same way. A company sells bonds to investors, promises regular interest, and agrees to return the original amount on a set date. The regular interest payment is often called the coupon, and the set date is the maturity.

Few investors can study every borrower in depth. Many lean on a rating as a quick signal, much as a landlord leans on a reference letter.

Reading the ladder from AAA down to D

The three agencies that dominate the market are S&P Global, Moody’s Investors Service and Fitch Ratings. StoneX says they control nearly 95% of the bond rating market. S&P and Fitch run their scale from AAA down to D, which stands for default. Moody’s runs from Aaa to C.

The scale has two broad zones, as Fidelity Canada describes it:

• Investment grade: BBB- (Baa3 at Moody’s) and above, covering the AAA, AA, A and BBB families.
• High yield, also called speculative or junk: anything below that line, from BB+ down.

Plus and minus signs at S&P and Fitch, and numbers at Moody’s, show where a bond sits inside a family. An A- is a notch below an A, for example.

The line between BBB- and BB+ is the one most watched. It separates the borrowers the market treats as sturdy from those it treats as risky, so a move across it can change how a company is seen overnight.

Why the grade changes the price of borrowing

Lower-rated bonds generally pay higher yields, which Fidelity says compensates investors for the added risk. Investment-grade bonds carry the lowest default risk and the smallest yields, according to StoneX. The rating therefore feeds into the interest a company must offer to attract buyers.

Yield and price move in opposite directions. If investors grow nervous about a borrower, they pay less for its existing bonds, and the yield on those bonds rises. A downgrade can hurt a bond’s price if the holder sells before maturity.

The gap between what a risky borrower pays and what a safe one pays is often called the spread. A wide spread means investors want a lot of extra payment for taking the risk. A narrow one means they see little difference.

The borrower’s side is simple. A higher grade means cheaper money and a wider pool of willing buyers. That is why companies guard their ratings carefully.

Where it shows up in AI spending

Our report on Microsoft’s planned $25 billion bond sale shows the idea at work. CNBC noted that Microsoft holds a top-tier AAA rating from S&P. It also quoted finance chief Amy Hood as saying the company has access to the debt markets because of its ratings and had not yet tapped them.

The same report describes a contrast. According to CNBC, Alphabet, Meta and Amazon posted negative free cash flow in recent quarters, and Oracle announced a plan to raise $10 billion of new debt. Free cash flow is the cash left after a company pays for its operations and investments. Microsoft’s was positive, according to that account.

Read together, those lines show why the grade matters. A company that spends faster than it earns must borrow, and the price of that borrowing depends on how lenders view it. CNBC also notes that investors have become more wary of heavily indebted companies as central bankers raise interest rates to fight inflation.

The same data center can therefore be financed in very different ways. Our earlier coverage of financing becoming as important as chips looked at leases and lender-backed structures. A AAA borrower can sell ordinary bonds, while a smaller player may need more complex structures. The details of any single deal should be read as reported by the outlets covering it, not as confirmed by us.

What a grade cannot tell you

A rating is an opinion, not a guarantee. A few limits are worth keeping in mind:

• Methods differ. StoneX notes that each agency uses its own criteria, so grades from different agencies may not match exactly.
• Grades move. Ratings change with an issuer’s financial health, and the forward-looking parts are predictions.
• A grade is not advice. It says nothing about whether a bond is a good price, and the rating cannot predict whether an investment will rise or fall in value.

For AI, that last point matters most. A top grade shows a company can likely repay. It does not show that a very large build-out will pay for itself.

The grade is also a summary of the past and present. It cannot foresee a sudden change in demand for AI services, a shift in chip prices or a new rule. Readers should treat it as one input among several.

What to watch as AI borrowing grows

Three signals are worth tracking. The first is whether more large technology companies sell investment-grade bonds to fund data centers. The second is whether rating agencies change outlooks or grades as debt rises. The third is how much extra yield investors demand from the weaker-rated borrowers compared with the strongest ones.

Each shows how the market prices the risk of AI spending, in a form that a plain letter grade makes easy to follow. When the spread between strong and weak borrowers widens, it suggests lenders are becoming choosier. When it narrows, it suggests they are comfortable funding the build-out.