When a company or government needs to raise money, it has two main options. It can sell ownership — that's a stock. Or it can borrow money and promise to pay it back with interest — that's a bond.
When you buy a bond, you're acting as the lender. The borrower — a corporation, the U.S. government, a city, or a state — promises to pay you a fixed amount of interest on a regular schedule, and then return your original investment at the end of a set period of time called the maturity date.
A simple example
You buy a $1,000 bond from the U.S. government with a 4% interest rate and a 10-year maturity. Every year for 10 years the government pays you $40 in interest (4% of $1,000). At the end of year 10 they return your original $1,000. You've earned $400 in interest over the decade, and you got your money back.
That's it. A bond is a loan with a contract attached to it — spelling out exactly how much you'll be paid and when you'll be paid back.
How bonds differ from stocks
The key difference between a stock and a bond comes down to what you own and what you're owed.
Stocks — ownership
You own a piece of the company. If the company does well, your piece becomes more valuable. If it fails, you could lose everything. Higher potential reward, higher risk. No guaranteed return.
Bonds — a loan
You lend money to the company or government. They owe you a fixed payment on a fixed schedule. Lower potential reward, lower risk. The return is known upfront — as long as the borrower doesn't default.
Think of it this way. If a friend asks you for money to start a business, you have two choices. You could become a part-owner — sharing in the profits if it succeeds and the losses if it fails. Or you could lend them the money at a set interest rate — getting paid back regardless of how well the business does, as long as they don't go under. A stock is the first option. A bond is the second.
Who issues bonds?
U.S. Treasury bonds
Issued by the federal government. Considered the safest bonds in the world — backed by the full faith and credit of the United States. Lower interest rates because the risk is so low.
Municipal bonds
Issued by states, cities, and local governments. Often exempt from federal taxes — useful for higher-income investors. Used to fund schools, roads, and public infrastructure.
Corporate bonds
Issued by companies. Higher interest rates than government bonds because companies carry more risk than governments. A company can go bankrupt — a government rarely does.
High-yield bonds
Also called "junk bonds." Issued by companies with lower credit ratings. Highest interest rates — because the risk of default is highest. Not recommended for beginners.
The risk of bonds
Bonds are generally considered safer than stocks — but they're not without risk. There are two main things that can go wrong.
Default risk — the borrower can't pay you back. This is rare for U.S. government bonds and uncommon for large, established corporations, but it does happen. The higher the interest rate a bond offers, the more the market is signaling that there's a real chance the borrower might default. High returns on bonds are a warning sign, not a gift.
Interest rate risk — when interest rates rise, existing bond prices fall. This is because a bond paying 3% becomes less attractive when new bonds are paying 5%. If you need to sell your bond before maturity during a period of rising rates, you may get less than you paid for it. If you hold to maturity, you get your full principal back regardless.
~4–5%
The approximate long-run average annual return of U.S. bonds — compared to roughly 10% for U.S. stocks. Bonds grow more slowly, but they fall less dramatically during market downturns. That stability is what makes them useful in a balanced portfolio.
Where bonds fit in a long-term strategy
For a young investor just starting out, bonds are not the priority. Time is your greatest asset, and stocks — specifically index funds — have historically produced far higher returns over long periods. If you're in your 20s or 30s and won't need the money for decades, a portfolio heavy in stock index funds is generally the right approach.
Bonds become more important as you get closer to retirement. As you age, you have less time to recover from a major market drop — so gradually shifting some of your portfolio from stocks to bonds helps protect what you've built. A common rule of thumb: subtract your age from 110 to get the percentage of your portfolio to hold in stocks. At 30, that's 80% stocks and 20% bonds. At 60, that's 50% stocks and 50% bonds.
This isn't a hard rule — it's a starting framework. But it captures the core idea: bonds are a tool for managing risk over time, not a path to building wealth from scratch.
Bond funds — the index fund version of bonds
Just as stock index funds let you own hundreds of stocks at once, bond index funds let you own hundreds of bonds at once — automatically diversified, at low cost. You don't have to research individual bonds or worry about a single borrower defaulting.
The most widely held bond index fund is BND — Vanguard's Total Bond Market ETF — which owns thousands of U.S. bonds across government and corporate issuers. FXNAX is Fidelity's equivalent. Both carry very low expense ratios and are available at every major broker.
Most beginners don't need a bond fund right away. But knowing it exists means you have a clear next step when the time is right — and you won't have to figure it out from scratch.
The bottom line
A bond is a loan with a contract. It pays steadier, more predictable returns than stocks — but lower ones over time. For young investors, bonds are less urgent than stock index funds. But understanding them completes the picture of how wealth is built and protected across a lifetime of investing.
Start with index funds. Learn bonds. Use both when the time is right.