OCT · ISSUE 42 · October 15, 2026
CONCEPTWhat AAA, BB and the rest actually mean on a bond
A credit rating is the grade that measures the risk that an issuer won't repay its debt. That letter sets the interest it will pay.
THE TOP GRADE
AAA
minimal default risk
THE BORDER
BBB-
investment grade vs junk
RISK ZONE
BB and below
more interest, more danger
THE IDEA
Better grade, less interest
the rating and the interest rate move in opposite directions
Three agencies grade the debt of companies and countries (you know them by their scales: AAA, AA, A, BBB...). The higher the grade, the lower the default risk the market sees, and the less interest it demands to lend. When a grade is cut, the interest rises.
THE BORDER
SIMPLE RULEBBB-
BBB-
the border: investment grade vs junk bond
Above BBB-, many funds can buy and the interest is moderate. Below it, the bond is deemed risky and has to pay far more to attract buyers.
This is the line that splits the debt world in two: above it, investment grade; below it, junk bonds (high yield).
- INVESTMENT GRADE
- — Debt from solid issuers, from BBB- and up.
- JUNK BOND
- — Debt rated BB+ and below: more risk and more interest (high yield).
IDEA
TO GET ITA rating is a probability, not a promise
“A rating does not promise you'll get paid. It tells you how many, out of every hundred similar issuers, have stopped paying in the past.”
A high grade does not guarantee you'll be paid; it only says that, historically, issuers like this default very rarely.
- PROBABILITY
- — The historical frequency of something happening, not a certainty.
- AGENCY
- — The independent body that analyzes and assigns the credit grade.
THE CURVE
HOW IT WORKSThe worse the grade, the more default risk spikes
The gap between AAA and A is small. The gap between B and CCC is enormous. That is why the market watches the bottom rungs so closely.
Conceptual curve, not real data. As the rating falls, the historical default probability does not rise gradually: it spikes at the bottom.
- RUNG
- — Each step on the ratings scale (from AAA downward).
- NON-LINEAR
- — When risk does not grow at a steady pace but accelerates.
KEYS
FOUR IDEASWhat the grade tells you (and what it doesn't)
WHO SETS THE GRADE
Independent agencies analyze the issuer's books and assign a letter. It is not infallible: in 2008 many high grades turned out to be wrong.
THE GRADE SETS THE INTEREST
The worse the rating, the more interest the market demands to lend. A downgrade instantly raises the cost of all the issuer's future debt.
THE BBB- BORDER MATTERS
Many funds can only hold investment grade. If a bond falls below BBB-, those funds are forced to sell and its price collapses.
THE MARKET RUNS AHEAD
The bond's price and its insurance (CDS) tend to move before the agency changes the grade. The rating confirms; the market anticipates.
The rating is a good first filter, but it does not replace looking at the price the market itself puts on the risk.
- DOWNGRADE
- — When an agency lowers an issuer's grade.
- CDS
- — Insurance that pays out if the issuer defaults; its price measures the fear.
THE SPLIT
EXAMPLEHow a bond market splits by grade
Minimal risk, low interest
Solid, moderate interest
Investment grade, but the most watched
More interest, more default risk
The BBB rung is the most crowded and the most delicate: a downgrade tips it into 'junk' and forces many funds to sell. That is where credit crises are born.
Illustrative split of a corporate debt market. Most is investment grade; the risk tail is what delivers the shocks.
- CREDIT QUALITY
- — How reliable an issuer is at repaying its debt.
- FORCED SELLING
- — When a fund must sell by rule, not by its own choice.
WATCHLIST
TO SEE ITWhere to see credit ratings in practice
| LQD | ~109 | → ref | Investment-grade corporate bonds (BBB- or better). The 'safe' side of credit. |
| HYG | ~79 | → ref | Junk bonds (BB and below). They pay more interest for more default risk. |
| AGG | ~99 | → ref | The broad bond market: a mix of government and high-grade corporate debt. |
| EMB | ~92 | → ref | Emerging-market debt. Lower grades, higher interest. |
| BIL | ~100 | → ref | US Treasury bills, the benchmark AAA debt: the lowest default risk there is. |
Example tickers to see the concept in the real world. Approximate levels, no day prices.
- ETF
- — A listed basket that groups many bonds of one type or quality.
- EMERGING
- — A developing country, with more risk and therefore lower grades.
WRAP
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- RATING
- — The credit grade that measures an issuer's default risk.
- INVESTMENT GRADE
- — The highest-quality debt, from BBB- and up.