Bonds & RatesExplainer
What do bond credit ratings like AAA and BBB actually tell you?
A credit rating is an agency's opinion of how likely a bond issuer is to pay. Learn the AAA-to-D scale, the investment-grade line and the limits of ratings.
Quick answer
A bond credit rating is an agency's assessment of how able an issuer is to pay its debts. Scales usually run from AAA at the top to D for default. BBB- or higher is investment grade; lower is high-yield. A rating is an opinion, not a guarantee.
Key points
- A credit rating is an agency's assessment of an issuer's ability to pay; it is not a recommendation to buy, sell or hold.
- A typical scale runs from AAA down to D (default); BBB- and above is investment grade, below that is non-investment grade or high-yield.
- Lower-rated bonds generally pay higher interest to compensate for a higher risk of default.
- Ratings can change at any time, and the SEC says they should add to, not replace, your own research.
What is a bond credit rating?#
The SEC's investor bulletin on credit ratings defines a credit rating as an assessment of the creditworthiness of a debt instrument or obligor, based on a rating agency's analytical models, assumptions and expectations[1]. Put simply, it is a professional opinion about how likely a borrower is to pay its debts in full and on time.
That matters because of credit risk, which the SEC defines as the risk that a company will fail to timely make interest or principal payments and thus default on its bonds[2]. FINRA notes that, other than U.S. Treasury securities, most bonds face some degree of credit risk, which is often indicated by the bond's credit rating[3]. If you are new to bonds, start with what a bond is.
How does the rating scale work, from AAA to D?#
The SEC describes a typical credit rating scale as having a top rating of AAA and a lowest rating of D, which indicates default[1]. Each agency defines its own symbols, so the exact meaning of a letter depends on who issued it[1]. Moody's, for example, writes its lower investment-grade boundary as Baa3 rather than BBB-[4].
| Rating category | Group | What it signals |
|---|---|---|
| AAA | Investment grade | Top of the scale |
| AA and A | Investment grade | Assessed lower likelihood of default than lower categories |
| BBB (down to BBB-) | Investment grade | Lowest investment-grade category |
| BB and B | Non-investment grade (high-yield) | Below BBB-; speculative grade |
| CCC, CC and C | Non-investment grade (high-yield) | Further down the speculative range |
| D | Default | The issuer has not paid |
Scale and BBB- dividing line from the SEC's ABCs of Credit Ratings, which also says a higher rating means the agency assesses a lower likelihood of default[1]. Some agencies add + and - signs or numbers within a category; check the issuing agency's definitions.
Where the investment-grade line falls
What is the difference between investment grade and high-yield?#
The SEC states that a rating of BBB- or higher is investment grade and a rating below BBB- is non-investment grade, also called speculative or high-yield[1]. FINRA draws the line in similar terms: bonds rated below Baa3 by Moody's or below BBB by S&P and Fitch are considered speculative-grade or high-yield[4].
Investor.gov explains why the label matters: investment-grade bonds are considered more likely to be paid on time, while non-investment-grade bonds generally offer higher interest rates to compensate investors for greater risk[5]. FINRA adds that the risks of default are typically higher for companies that issue high-yield bonds[4].
Worked example
Worked example: what the extra yield pays for
Put $10,000 into each of two five-year bonds: one rated AA paying 4.5%, one rated BB paying 7%. The rates are illustrative. The BB bond pays $250 more a year — a 250-basis-point gap — or $1,250 more over five years if every payment arrives. Now suppose, purely as an illustration, the BB issuer pays two years of interest and then defaults, and investors recover 40% of principal (an assumed figure, not a statistic). You would get back $5,400 in total, a $4,600 loss, against $12,250 from the AA bond if it pays in full.
| Scenario ($10,000 each) | Yearly interest | Total received over 5 years | Gain or loss |
|---|---|---|---|
| AA bond at 4.5%, paid in full | $450.00 | $12,250.00 | +$2,250.00 |
| BB bond at 7%, paid in full | $700.00 | $13,500.00 | +$3,500.00 |
| BB bond defaults after year 2, 40% recovered | $700.00 for 2 years | $5,400.00 | -$4,600.00 |
Figures computed in code from the stated inputs; rounded to the nearest cent or tenth.
The point is not that one bond is better. It is that the higher yield is payment for a real chance of the bad row. Compare yields only between bonds of similar quality — see bond yield explained, and basis points for the unit used to quote yield gaps.
Who gives out credit ratings, and who pays them?#
In the U.S., rating agencies registered with the SEC are called nationally recognized statistical rating organizations, or NRSROs[1]. The SEC's list of current NRSROs, last updated March 27, 2026, names 11 firms, including S&P Global Ratings, Moody's Investors Service, Fitch Ratings, DBRS, Kroll Bond Rating Agency and A.M. Best Rating Services[6].
Credit ratings and the SEC: key facts
Two limits are worth knowing. SEC registration is not an endorsement of an agency or of any rating it issues, and by law the SEC is not permitted to regulate the substance of ratings or the methods NRSROs use[1]. And many agencies are paid by the issuers they rate, which the SEC flags as a potential conflict of interest[1]. Rules for rating agencies differ by country; this section describes the U.S. system.
What are the limits of credit ratings?#
The SEC is direct about this. A credit rating is not a guarantee that a financial obligation will be repaid, and it should not be read as investment advice or as a recommendation to buy, sell or hold[1]. Rating changes can happen at any time, without warning and at any rating level[1].
The SEC's advice is that if you use credit ratings, they should be in addition to, and not a replacement for, your own research[1]. Registered agencies must post performance statistics on their websites each year, which lets you see how their past ratings held up[1].
How can a beginner use ratings sensibly?#
Find the rating and the agency
Note which NRSRO issued it, since each agency defines its own symbols.
Check which side of the line it sits
BBB- or higher is investment grade; anything lower is high-yield.
Ask why the yield is what it is
Non-investment-grade bonds generally pay more to compensate for greater risk[5]. A yield well above similar bonds is a reason to look harder, not a bargain.
Think about concentration
One default hurts most when one issuer is a large share of your money. The SEC notes that spreading investments across a wide range of companies can help lower risk[8] — see bond funds vs individual bonds.
Watch for changes
Ratings can be cut without warning, so a rating at purchase is not a permanent label.
What mistakes do beginners make?#
Reading a rating as a buy signal
The SEC says a rating is not a recommendation to buy, sell or hold[1]. It is one input about default risk.
Assuming investment grade means no risk
Investment-grade issuers can be downgraded or default, and their bonds still carry interest rate risk.
Comparing letters across agencies without checking
Each agency defines its own symbols[1]. FINRA, for example, describes high-yield bonds as those rated below Baa3 by Moody's or below BBB by S&P and Fitch[4] — different letters for the same idea.
Chasing yield in high-yield bonds
Higher coupons exist because default risk is higher. Size any high-yield holding so that one default would not derail your plans.
What else do beginners ask?#
What does a AAA rating mean?
It is the top of a typical rating scale, and a higher rating means the agency assesses a lower likelihood of default[1]. It is still an opinion, not a guarantee.
Are BBB bonds safe?
BBB- and above counts as investment grade[1], but BBB is the lowest investment-grade category. A downgrade by one notch below BBB- would move a bond into high-yield.
Do credit ratings matter for Treasury securities?
FINRA notes that, other than U.S. Treasury securities, which are generally deemed free of default risk, most bonds carry some credit risk often indicated by a rating[3]. Ratings matter most when you compare bonds that do carry credit risk, such as corporate bonds.
Can a bond's rating change after I buy it?
Yes. The SEC says rating changes can happen at any time, without warning and at any level[1].
What is the bottom line?#
A credit rating is an agency's opinion of how likely a borrower is to pay. The scale runs from AAA to D, and the line between investment grade and high-yield sits at BBB-. Lower ratings come with higher yields because default is more likely. Use ratings as one input — alongside the yield, the maturity and your own research — and remember that the SEC itself says a rating is not a guarantee and not advice.
Sources
Numbers in brackets in the text point here. Grade A = primary source (regulator, statistics agency, law or official document).
- 1
- 2
- 3
- 4
- 5
- 6
- 7
- 8