How government and corporate debt works, why bond prices move opposite to interest rates, and the role of fixed income in a portfolio.
When you buy a bond, you are acting as a lender. The issuer — a government, municipality, or corporation — is the borrower. In exchange for your money, the issuer promises to pay you a fixed rate of interest at regular intervals and to return your original loan amount on a specified future date.
Bonds are called "fixed income" securities because the payments are predetermined and contractually obligated. Unlike stocks, where dividends can be cut and prices fluctuate with company performance, a bond's payments are fixed in advance. A bondholder who holds to maturity knows exactly how much they will receive and when — unless the issuer defaults.
This is the single most counterintuitive and important concept in bond investing: when interest rates rise, existing bond prices fall — and vice versa. Understanding why requires working through the math.
This relationship is why bond investors feared rising rates in 2022. When the Federal Reserve raised rates from near 0% to 5.5% in 16 months — the fastest tightening in 40 years — many long-term bond funds lost 20–30% of their value.
Current yield is simply the annual coupon divided by the current market price. If you paid $900 for a bond with a $50 annual coupon: Current Yield = $50 / $900 = 5.56%. This understates the total return because it ignores that you will receive $1,000 at maturity — a $100 gain above your $900 purchase price.
Yield to maturity is the total annualized return if you hold the bond until it matures, accounting for all coupon payments plus the gain or loss from price to par value. It is the most accurate measure of a bond's true return. A bond trading at a discount (price below $1,000) will have a YTM above its coupon rate; a bond trading at a premium will have a YTM below its coupon rate.
The US government issues several types of debt obligations, collectively called "Treasuries." They are considered the closest thing to a risk-free investment because they are backed by the full faith and credit of the United States government — which has the unique ability to print dollars and has never defaulted on its debt.
| Security | Maturity | How It Works | Typical Use |
|---|---|---|---|
| Treasury Bills (T-Bills) | 4 weeks to 52 weeks | Sold at discount, no coupon — you buy $980, receive $1,000 at maturity | Cash management, emergency fund alternative |
| Treasury Notes (T-Notes) | 2, 3, 5, 7, 10 years | Pay semi-annual coupons | Most commonly traded Treasury — the "10-year yield" is the global benchmark |
| Treasury Bonds (T-Bonds) | 20 and 30 years | Pay semi-annual coupons, highest interest rate risk | Long-term investors, pension funds |
| TIPS | 5, 10, 30 years | Principal adjusts with CPI; coupon rate stays fixed but applied to growing principal | Inflation protection — real return guaranteed |
Corporations borrow by issuing bonds, paying higher interest rates than governments because there is a real possibility (however small) that the company could fail and be unable to repay. Credit rating agencies assess each issuer's creditworthiness and assign ratings.
State and local governments issue municipal bonds ("munis") to finance infrastructure, schools, and public projects. The critical advantage: interest income from most municipal bonds is exempt from federal income tax and often exempt from state taxes too. This makes them especially valuable for high-income investors in the highest tax brackets.
Eurobonds are bonds issued in a currency other than the home currency of the country where they are issued — for example, a US dollar bond issued in Europe. Emerging market bonds are issued by governments or corporations in developing economies (Brazil, Mexico, Indonesia, South Africa). They offer higher yields but come with additional risks: currency risk (the local currency may depreciate against the dollar), political risk, and less liquidity.
Three agencies dominate global bond rating: Moody's, Standard & Poor's (S&P), and Fitch. Their role is to assess an issuer's ability and willingness to repay debt, assigning letter grades that guide investor decisions.
| Moody's | S&P / Fitch | Category |
|---|---|---|
| Aaa | AAA | Highest quality |
| Aa1/Aa2/Aa3 | AA+/AA/AA- | Very high quality |
| A1/A2/A3 | A+/A/A- | Upper-medium grade |
| Baa1/Baa2/Baa3 | BBB+/BBB/BBB- | Investment grade minimum |
| Ba1/Ba2/Ba3 | BB+/BB/BB- | Speculative / Junk |
| B through C | B through D | Highly speculative to default |
The 2008 financial crisis exposed a catastrophic conflict of interest in the rating agencies. Banks paid agencies to rate the mortgage-backed securities they were creating — and the agencies, competing for business, assigned AAA ratings to securities filled with subprime loans that should have been rated junk. When housing prices fell, these AAA-rated securities lost 70–90% of their value. The Dodd-Frank Act of 2010 attempted to reform rating agency accountability, but their fundamental business model — issuers paying for their own ratings — remains largely unchanged.
The yield curve plots interest rates (yields) on the vertical axis against maturities (time to repayment) on the horizontal axis for US Treasury securities. Its shape contains powerful signals about economic expectations.
Longer-term bonds yield more than short-term bonds. This is the historically normal state: lenders demand higher compensation for tying up money for longer periods. A 3-month T-Bill might yield 3% while a 10-year T-Note yields 4.5%.
Short and long-term rates are similar. This often signals a transition — either rates are about to rise (which would bring long rates up) or the economy is slowing (which would bring short rates down).
Short-term rates are higher than long-term rates. This is historically rare and powerful as a recession predictor. An inverted yield curve preceded every US recession since 1970 without a single false positive. The inversion in 2006 predicted the 2008 recession. The inversion in 2019 predicted the 2020 recession. The yield curve inverted again in 2022-2023, deeply so — with 2-year Treasury yields exceeding 10-year yields by over 1%. Whether this inversion will predict another recession remains to be seen as of mid-2024.
Duration measures how sensitive a bond's price is to changes in interest rates. A bond with a duration of 7 years will lose approximately 7% of its value if interest rates rise 1%, or gain 7% if rates fall 1%. Duration increases with maturity and decreases with coupon rate (because higher coupons return cash sooner, reducing average wait time for payment).
This is why long-term bonds are far riskier in a rising rate environment. In 2022, 30-year Treasury bonds lost over 40% of their market value as the Fed raised rates by 5.25 percentage points — one of the worst bond market performances in history.
Bonds serve several roles in a diversified investment portfolio:
Important caveat: The 2022 experience broke this historical pattern. Both stocks and bonds fell simultaneously — the S&P 500 dropped 18% and the Bloomberg US Aggregate Bond Index dropped 13% in the same year. When the cause of a stock market decline is rising inflation (which the Fed fights by raising rates), bonds do not provide their usual hedge. This reminded investors that "negative correlation" is not a law of nature — it is a historical tendency that can break down.