What a corporate bond is — how a company borrows without a bank
A corporate bond is an IOU a company issues to borrow directly from investors instead of from a bank. It promises a fixed rate of interest for a fixed period and repayment of principal at maturity, and the interest rate depends on how credible the market judges that promise to be
The three lines
- Structure — an IOU sold directly to investors with the coupon and maturity fixed in advance
- Pricing — the matching government bond yield plus a spread that prices default risk
- Risk — unlike a bank deposit, principal is not protected; the investor bears the loss
Key questions
- What is a corporate bond in plain terms?
- It is an IOU written by a company. 'Lend us this money, we will pay 4% each year for five years, and return the principal at the end.' That promise is documented, divided into small units, and sold to many investors. Instead of borrowing a large sum from one bank, the company borrows small amounts from a wide market.
- How is a corporate bond different from a bank loan?
- The lender and the negotiation differ. A bank loan involves one counterparty and individually negotiated terms. A corporate bond sets terms in advance, publishes them, and gathers whoever will buy. Bonds generally allow far larger amounts and are not constrained by a bank's lending limits or internal approval. In exchange, the company must accept a public credit rating and take whatever the market mood allows — in a poor market the issue may not clear at the intended rate.
- How is the interest rate on a corporate bond determined?
- In two layers. The base layer is the yield on a government bond of the same maturity, the baseline price of money. The upper layer is the spread, which prices the chance the company fails to repay. A strong rating makes that layer thin; a weak one makes it thick. In August 2026, with the US 30-year Treasury at 5.31%, Alphabet's 30-year corporate bond came at 6.4% — a spread of 1.15 percentage points.
- Should an individual buy corporate bonds? How do they differ from deposits?
- A deposit is protected up to an insured limit; a corporate bond carries no such protection. If the issuer defaults, principal can be lost. Selling before maturity introduces a second risk: the price then depends on prevailing market rates, and if rates have risen since issue, the bond is worth less than face value. The higher interest exists precisely because the investor carries both risks.
In the summer of 2026, "corporate bond issuance by AI companies" was named repeatedly as one of the forces pushing US long-term Treasury yields to a 19-year high. Alphabet borrowed at 6.4%; Meta's data centre paper cleared above 7.5%.
Reading those sentences requires knowing what a corporate bond is.
1. The shortest definition
A corporate bond is an IOU written by a company.
"Lend us this money. We will pay 4% each year for five years, and return the full principal at the end."
That promise is documented, divided into small units, and sold to many investors. Instead of one large loan from one bank, the company borrows a little from a wide market.
| Element | Name | Example |
|---|---|---|
| Unit of borrowing | Face value | $1,000 |
| Promised interest | Coupon rate | 4% per year |
| Repayment date | Maturity | 5 years |
| Actual market return | Yield | Moves continuously |
The last row is what beginners most often miss. The coupon is fixed at issue and never changes; the price the bond trades at does.
2. Against a bank loan
| Item | Bank loan | Corporate bond |
|---|---|---|
| Lender | One bank (or a small syndicate) | Many investors in a market |
| Terms | Individually negotiated | Published, then demand is gathered |
| Credit assessment | Internal to the bank | Public rating agency grade |
| Selling before maturity | Effectively impossible | Tradeable in a secondary market |
| Scale | Constrained by bank limits | As large as the market absorbs |
| Sensitivity to market mood | Modest | High — a weak market means a failed issue |
The main reason companies choose bonds is scale. Funding a multibillion capital programme through bank loans alone requires syndication and runs into limits. A bond issue grows to whatever the market will take.
That is why bonds moved to the centre of AI data centre funding in 2026. Corporate bond funding across Amazon, Meta, Nvidia, Oracle and Alphabet rose from $39.7 billion in 2024 to $218.3 billion so far in 2026.
3. How the rate is built
A corporate bond rate stacks in two layers.
`` Corporate bond rate = matching-maturity government yield + credit spread ↑ the base price of money ↑ the price of doubt ``
The base layer is what that country's government pays to borrow for the same period. Governments can levy taxes, so they are treated as the safest borrower, and their yield becomes the floor under every other rate.
The upper layer is the spread — the market's price on the chance this company does not survive to repay.
The August 2026 US market gives real numbers.
| Issuer | Maturity | Rate | vs Treasury |
|---|---|---|---|
| US government | 30 years | 5.31% | baseline |
| Alphabet | 30 years | 6.4% | +1.15pp |
| Meta (data centre bonds) | not specified | above 7.5% | +2pp or more |
Both are among the strongest corporate credits on earth. Both still had to add one to two percentage points to raise thirty-year money. The longer the maturity and the less certain the use of proceeds, the thicker that layer becomes.
4. What a credit rating actually does
The grade assigned by a rating agency is the starting point for that spread.
| Band | Common name | Character |
|---|---|---|
| Upper grades | Investment grade | Eligible for pension funds and insurers |
| Below that | Speculative grade (high yield) | Higher coupon, sharply higher default risk |
This boundary matters more than any single notch, because many institutional investors are permitted by their own mandates to hold only investment grade. A downgrade across that line removes an entire class of buyers, and the issuer must pay far more to replace them. Rating changes show up in funding costs as a step, not a slope.
This is also where the 2026 warning about "the line around safe bonds eroding" comes from. As investment-grade issuers dramatically increase volume, questions grow about the gap between the label and the underlying risk.
5. What an individual is taking on
Individuals can buy corporate bonds through a broker. They are not deposits.
| Item | Bank deposit | Corporate bond |
|---|---|---|
| Principal protection | Insured to a limit | None |
| If the issuer fails | Paid within the insured limit | Principal can be lost |
| Early withdrawal | Forfeit some interest | Sell at market price — principal at risk |
| Return | Fixed interest | Interest plus trading gain or loss |
The second risk needs spelling out. When rates rise, the price of already-issued bonds falls. If you hold a bond paying 4% and new bonds arrive paying 5%, yours only sells at a discount. Held to maturity you receive the promised principal and interest; sold in between, that loss is realised.
This page set out that relationship on August 18, 2026 in "What a 30-year government bond is." Government or corporate, the mechanism is identical.
6. How corporate bonds pushed government yields up
What made August 2026 unusual is that the arrow ran backwards.
Normally government yields move first and corporate rates follow, because the base layer lifts the upper one.
In 2026, corporate issuance grew large enough that pension funds and insurers with thirty-year liabilities sold Treasuries to buy corporate paper. More sellers of Treasuries means lower Treasury prices, and lower prices mean higher yields. Bank of America calculates that increased corporate and mortgage bond supply added roughly 0.3 percentage points to the 2026 10-year yield.
That inversion of the textbook crowding-out effect is set out in "AI bonds hit $200 billion — it was not the government crowding out markets."
7. What this article could not confirm
- Korean market figures. All rate examples here are from the US market; Korean spreads by rating band as of August 2026 were not confirmed.
- Meta's 7.5%. The reporting does not specify which maturity or which issue.
- Individual purchase terms. Minimum sizes and tax treatment vary by broker and product and are not stated here as a single standard.
- Rating scale correspondence. Mapping between different agencies' notation was not individually verified.
Sources
- Newspim — Big tech's AI borrowing snags US long-term rates: the inverted crowding-out effect
- Financial News — AI rush drives a corporate bond boom as the line around 'safe' bonds erodes
- Global Economic — Meta's AI data centre borrowing cost jumps to 7.5%
- Financial News — Governments and AI firms both borrowing: US long rates at a 19-year high
- Investing.com — US 30-year bond yield historical data