Bond Basics — What is a bond?

To understand bonds, start with interest rates. Interest rate theory can fill libraries, but the core idea is simple: an interest rate is the fee charged for lending money. If I loan you $1,000, you eventually repay the $1,000. I may also require an annual fee—say $50—for the use of that money. That $50 is interest. Expressed as a percentage of the $1,000 loan, the interest rate is 5%:

$50 ÷ $1,000 = 0.05 (5%)

A bond is a debt instrument: a loan contract where an investor lends money to an issuer (often a government, municipality, or corporation). In return, the issuer typically pays interest over time and returns the principal at maturity. You are the lender; the issuer is the borrower.

Why do issuers borrow this way? The same reason households and companies borrow: they need money now for something large—roads, factories, operations—and repay over time. When you buy a bond, you are helping fund that borrowing.

Debt vs. equity: A stock (equity) represents ownership in a company. A bond (debt) does not. Bondholders are creditors. If the issuer does well, stockholders may benefit more; if the issuer struggles, bondholders usually stand ahead of stockholders in the repayment line—but bondholders can still lose money if the issuer defaults.

Many bonds pay a fixed coupon for the life of the bond. That is the classic “fixed income” idea. There are exceptions—floating-rate notes, inflation-linked bonds (such as TIPS), and zero-coupon bonds that pay no periodic interest and instead are issued at a discount to face value.

Also important: bonds are not automatically “safe.” U.S. Treasuries are generally treated as among the lowest credit-risk investments in the world, but even they can lose market value when rates rise if you sell before maturity. Corporate and municipal bonds add credit risk (the chance the issuer fails to pay). Inflation can reduce what your interest dollars buy.

Bond characteristics

Face value (par value / principal): the amount the issuer promises to repay at maturity (often $1,000 for corporate bonds; U.S. Treasuries commonly use $100 increments for quoting/trading)
Maturity: the date principal is due. Short-, intermediate-, and long-term bonds carry different interest-rate sensitivity
Coupon: the scheduled interest payment, usually quoted as an annual percentage of face value (many U.S. bonds pay coupons semi-annually)
Call feature (optional): if a bond is callable, the issuer may redeem it early under stated rules—often when rates fall and refinancing is cheaper

Today, most bonds are electronic book-entry records rather than paper certificates, but “face value” still means the principal amount used for coupon calculations and repayment at maturity.

Don’t confuse principal (the loan amount / face value) with “school principal.” Your mortgage payment mixes principal repayment and interest; a coupon bond’s regular payment is usually interest only, with principal returned at maturity (amortizing bonds exist, but that is a different structure).

Coupon rate vs. yield

The coupon rate is fixed on a traditional bond: a 5% coupon on a $1,000 face value means $50 of interest per year (often $25 twice a year).

Yield is about the return relative to the price you actually pay. If you buy that same bond for $1,000, a simple current yield is:

$50 ÷ $1,000 = 5%

Now suppose market interest rates rise and new comparable bonds pay 6% ($60 per year on a $1,000 par bond). Your older bond still pays only $50. Buyers will not pay full price for a lower coupon, so the market price falls. Roughly speaking, for current yield to approach 6%:

$50 ÷ market price ≈ 0.06 → market price ≈ $833

You still receive the $50 coupon if you hold the bond. If you bought at a discount and hold to maturity (and the issuer pays as promised), you also get face value back—so part of your total return can come from that price recovery. The more complete measure for holding to maturity is yield to maturity (YTM), which accounts for coupons, the purchase price, and repayment of principal. For callable bonds, investors also watch yield to call / yield to worst.

Rule of thumb: when market interest rates go up, existing bond prices usually go down. When rates go down, existing bond prices usually go up. That inverse relationship is the key price risk for bonds you may sell before maturity.

Why not just always set the market price equal to face value? Issuers need to raise a planned amount of money when bonds are first sold. After issuance, secondary-market trading lets prices adjust as rates, credit views, and demand change. That primary vs. secondary market split is covered next in Trading Bonds.