How Bonds Work

When the U.S. government needs to fund operations but doesn’t want to raise taxes, it borrows from investors by selling Treasury bonds. In 2025, the U.S. Treasury issued over $8 trillion in new debt according to the Treasury Bulletin. That’s not a typo. Trillions of dollars, borrowed from ordinary investors, pension funds, and foreign governments. Bonds are the machinery that makes this possible, and understanding them is essential for anyone who wants to build wealth.

The short answer

A bond is a loan you make to a government or company in exchange for regular interest payments and the return of your principal when the bond matures. When you buy a bond, you’re essentially becoming a lender. The issuer promises to pay you a fixed interest rate (the coupon) at set intervals and return your original investment at the end of the term. This makes bonds fundamentally different from stocks, which represent ownership in a company.

The full picture

What a bond actually is

At its core, a bond is an IOU. When you purchase a bond, you’re lending money to the issuer for a predetermined period. In return, the issuer agrees to pay you interest periodically and repay the full face value (called par) when the bond reaches its maturity date.

Let’s say you buy a 10-year Treasury bond with a face value of $1,000 and a 4% coupon rate. Every year, you’ll receive $40 in interest payments. At the end of 10 years, you’ll get your $1,000 back. That’s the basic transaction.

The interest rate on a bond is called the coupon rate because, in the old days, bonds came with physical coupons you’d clip and redeem for interest payments. Most bonds today pay interest electronically, but the terminology stuck.

Types of bonds

Not all bonds are created equal. The three main categories are government bonds, municipal bonds, and corporate bonds.

Government bonds are issued by national governments. In the United States, these are Treasuries, and they’re considered the safest investments in the world because the U.S. government has never defaulted on its debt. Treasury bonds (T-bonds) mature in 20-30 years, Treasury notes (T-notes) mature in 2-10 years, and Treasury bills (T-bills) mature in less than a year. Other countries issue bonds too: Germany’s Bunds, Japan’s JGBs, and the UK’s Gilts all function similarly. These markets are heavily influenced by how central banks work and their monetary policy decisions.

Municipal bonds are issued by cities, states, and other local governments to fund infrastructure projects like schools, highways, and water treatment facilities. These often come with a tax advantage: the interest is typically exempt from federal income tax and sometimes state and local taxes too.

Corporate bonds are issued by companies to raise money for expansion, acquisitions, or day-to-day operations. These carry more risk than government bonds because companies can (and sometimes do) go bankrupt. The interest rates on corporate bonds are generally higher to compensate for this additional risk.

How bond prices work

Here’s where it gets interesting: bonds can be bought and sold before they mature, and their prices fluctuate based on changes in interest rates. Understanding interest rates is essential to understanding bond pricing.

When interest rates rise, existing bonds with lower coupon rates become less valuable, so their prices fall. When interest rates fall, existing bonds with higher coupon rates become more valuable, and their prices rise. This is called interest rate risk, and it’s the primary risk investors face with bonds.

For example, if you bought a bond paying 3% interest and then market rates jumped to 5%, your bond is worth less because new investors can get better returns elsewhere. Conversely, if rates drop to 1%, your 3% bond becomes valuable because it pays more than new bonds.

This inverse relationship between interest rates and bond prices is one of the most important concepts in bond investing.

Credit ratings matter

Not all bonds are equally likely to be repaid. Credit rating agencies like Moody’s, Standard & Poor’s, and Fitch assign ratings to bond issuers based on their financial health and ability to repay debt. These agencies use similar rating systems to those used in how credit scores work, with AAA representing the highest credit quality.

Investment-grade bonds carry ratings of BBB- or higher from Standard & Poor’s. These issuers are considered likely to meet their payment obligations. High-yield bonds (also called junk bonds) have lower ratings and carry higher risk, which is why they offer higher interest rates to compensate investors.

The 2008 financial crisis made credit ratings famous for the wrong reasons: many mortgage-backed securities had inflated AAA ratings that turned out to be wildly optimistic. Always take ratings with a grain of salt.

Yield: your actual return

The coupon rate tells you what the bond pays, but yield tells you what you actually earn. Current yield is simply the annual interest payment divided by the bond’s current price. If a bond pays $40 per year but trades for $950, your yield is 4.2% ($40 ÷ $950).

Yield to maturity (YTM) is more complex but more useful: it accounts for both the interest payments you’ll receive and the gain or loss you’ll make if you hold the bond until it matures. This is the number professionals use when comparing bonds.

Why it matters

Bonds serve a fundamentally different purpose than stocks in a portfolio. Stocks offer growth potential but come with significant volatility. Bonds offer stability and predictable income. In a diversified portfolio, they act as a buffer against market downturns.

Consider the 2008 financial crisis: the S&P 500 fell 38% that year, but the 10-year Treasury yield dropped from 3.9% to 2.2%, meaning Treasury bonds actually gained value as investors fled to safety. Bonds didn’t just preserve capital during the crash, they offset some of the losses from stocks.

For retirees or anyone needing predictable cash flow, bonds are irreplaceable. If you need $40,000 per year in retirement income, you can buy bonds that guarantee exactly that. No stock market volatility, no wondering if your portfolio will survive a downturn.

And with interest rates at historic highs in 2024-2025, bonds offer yields not seen in over a decade. The 10-year Treasury was yielding around 4.3% in early 2025, compared to near-zero just three years earlier. For income-focused investors, this represents a genuine opportunity.

Common misconceptions

“Bonds are completely safe.”

This is wrong. While U.S. Treasury bonds are considered virtually risk-free, other bonds carry real risk of default. Corporate bonds can and do fail, especially during economic downturns. Even municipalities have gone bankrupt (Detroit filed for Chapter 9 in 2013). Learn more about how bankruptcy works to understand what happens when issuers can’t repay their debts. The safety of your bond investment depends entirely on the issuer’s financial health.

“You should only hold bonds when interest rates are falling.”

This myth traps investors. If you wait for rates to fall, you miss out on the higher yields available when rates are elevated. The smart approach is to hold bonds across different maturities (a bond ladder) so you’re continuously reinvesting and can take advantage of rate changes over time.

“Bonds always lose money when interest rates rise.”

Not true. If you hold a bond to maturity, you get your full principal back regardless of rate changes. You only lose money if you’re forced to sell before maturity at a bad time. For long-term investors who can hold to maturity, rate changes are noise, not loss.