Bonds

Definition: A bond is a loan an investor makes to a government or company in exchange for periodic interest payments and repayment of principal at maturity.

How It Works

The issuer (a government, municipality, or corporation) borrows a fixed amount of money, called the face value or par value, usually issued in units of $1,000 or $100
In exchange, the issuer promises to pay a stated interest rate, called the coupon rate, on a regular schedule (commonly semiannually) for the life of the bond
At the maturity date, the issuer repays the full face value to whoever currently holds the bond at that time
Bonds are first sold in the primary market, often through an auction process run directly by the issuer or its underwriters
They can then be bought and sold among investors in the secondary market before they mature, where their price fluctuates with market conditions
Bond prices move opposite to prevailing interest rates
When market rates rise, existing bonds with lower fixed coupons become less attractive, so their price falls to compensate a new buyer with a higher effective yield
When rates fall, existing bonds with higher coupons become more valuable relative to new issues, and their price rises

The Anatomy of a Bond

Face value (par value): the amount repaid at maturity and the base on which the coupon is calculated
Coupon rate: the fixed annual interest rate stated on the bond, paid as cash income to the holder
Maturity: the date the principal is repaid; can range from a few months (Treasury bills) to 30+ years (long bonds)
Issuer: the government or company that borrowed the money and is obligated to repay it
Yield: the actual return an investor earns, which differs from the coupon rate once the bond trades away from its face value
CUSIP or ISIN: a unique identifier used to track the specific bond issue in trading systems

How Bond Pricing Works

A bond’s fair price is the present value of all its future cash flows — coupon payments plus the final principal repayment — discounted at the prevailing market interest rate, $r$ :

P = \sum_{t=1}^{n} \frac{C}{(1+r)^t} + \frac{F}{(1+r)^n}

Where:

$P$ is the bond’s price today
$C$ is the periodic coupon payment
$F$ is the face value repaid at maturity
$r$ is the market discount rate per period
$n$ is the number of periods remaining until maturity

Worked example: Take a bond with a $1,000 face value, a 5% annual coupon ($50 per year), and 3 years to maturity.

If the market interest rate for comparable bonds is also 5%, the bond prices at exactly $1,000 (trading “at par”)
If market rates rise to 7% after issuance, the same bond’s price falls, since new bonds now offer a more competitive coupon:

P = \frac{50}{1.07} + \frac{50}{1.07^2} + \frac{1050}{1.07^3} \approx 947.49

The bond now trades at a discount to face value, because it must be cheaper to offer a buyer a return competitive with newer, higher-coupon bonds
If rates instead fell to 3%, the same bond would trade at a premium above $1,000, since its above-market coupon becomes more valuable

Types of Bonds

Government/Treasury bonds: issued by national governments (e.g., U.S. Treasuries); generally considered the lowest credit risk in their own currency
Municipal bonds (“munis”): issued by states, cities, or local authorities, often with tax-exempt interest income
Corporate bonds: issued by companies to fund operations, expansion, or acquisitions; risk and yield vary widely by issuer
- Investment-grade bonds: issued by financially strong companies with a lower risk of default and correspondingly lower yields
- High-yield (“junk”) bonds: issued by companies with weaker credit profiles; pay higher coupons to compensate investors for greater default risk
Zero-coupon bonds: pay no periodic interest; instead sold at a deep discount to face value and redeemed at full face value at maturity, with the discount itself functioning as the interest earned
Inflation-linked bonds (e.g., U.S. TIPS): principal adjusts with inflation, protecting the holder’s purchasing power over time
Callable bonds: give the issuer the right to repay the bond early, usually when interest rates fall and refinancing at a lower rate becomes attractive for the issuer
Convertible bonds: can be converted into a predetermined number of the issuing company’s shares, blending fixed bond income with potential equity upside
Agency bonds: issued by government-affiliated entities, carrying slightly more risk than sovereign debt but usually less than corporate bonds

Bond Credit Ratings

Independent agencies grade an issuer’s ability to repay debt on time. The scale runs, roughly, from safest to riskiest:

Rating band	Moody’s	S&P / Fitch	Meaning
Highest quality	Aaa	AAA	Minimal default risk
High quality	Aa	AA	Very low default risk
Upper medium	A	A	Low default risk
Lower medium (investment grade cutoff)	Baa	BBB	Adequate capacity to repay
Speculative	Ba, B	BB, B	Elevated default risk (“junk”)
Highly speculative	Caa and below	CCC and below	Substantial or near-certain risk of default

Anything at Baa3/BBB- or above is considered investment grade; anything below is high-yield or “junk”
A rating downgrade typically pushes a bond’s price down (and its yield up), since investors demand more compensation for the added risk

Yield: Coupon Rate vs. Current Yield vs. Yield to Maturity

Coupon rate: the fixed rate printed on the bond, based on face value — this never changes over the bond’s life
Current yield: the annual coupon payment divided by the bond’s current market price; this moves as the bond’s price moves
Yield to maturity (YTM): the total annualized return an investor earns if the bond is held until maturity, accounting for coupon income, any price gain or loss relative to face value, and the time value of money
YTM is the most complete single measure of a bond’s expected return and is the number most often quoted when comparing bonds

Duration: Measuring Interest Rate Sensitivity

Duration estimates how much a bond’s price will change for a given change in interest rates, expressed in years
As a rule of thumb, a bond with a duration of 7 will lose roughly 7% of its value if rates rise by 1 percentage point, and gain roughly 7% if rates fall by 1 percentage point
Longer-maturity bonds generally have higher duration, and are therefore more sensitive to rate changes, than short-maturity bonds
Bonds with higher coupon rates have somewhat lower duration than otherwise similar bonds with lower coupons, because more of their return arrives sooner in the form of cash payments

Bond Risk Factors

Interest rate risk: rising rates reduce the market value of existing bonds, especially longer-duration ones
Credit/default risk: the chance the issuer fails to make interest payments or repay principal in full
Inflation risk: fixed coupon payments lose real purchasing power if inflation rises faster than expected
Liquidity risk: some bonds, especially smaller municipal or corporate issues, can be hard to sell quickly without accepting a lower price
Call risk: callable bonds may be redeemed early by the issuer, forcing the investor to reinvest at lower prevailing rates
Reinvestment risk: coupon payments received along the way may have to be reinvested at lower rates than the original bond offered
Currency risk: for bonds issued in a foreign currency, exchange rate swings can add or subtract from returns independent of the bond’s own performance (see Exchange Rate)

How Bond Prices Are Quoted

Bond prices are typically quoted as a percentage of face value rather than a dollar amount, so “98” means the bond trades at 98% of par
A bond trading below 100 is trading “at a discount”; above 100 is trading “at a premium”; exactly at 100 is trading “at par”
Accrued interest since the last coupon payment is usually added separately when a buyer actually settles a trade

Bonds vs. Stocks

	Bonds	Stocks
Legal claim	Creditor (owed a debt)	Owner (equity stake)
Typical income	Fixed coupon payments	Variable, optional dividends
Priority if issuer fails	Paid before shareholders	Paid last, after all creditors
Typical volatility	Lower	Higher
Upside potential	Capped near face value plus coupons	Theoretically unlimited
Common role in a portfolio	Income and stability	Growth

Why It Matters

Bonds offer more predictable income and lower volatility than stocks, making them a common tool for balancing risk in a portfolio
Because bond and stock prices often move somewhat independently of each other, adding bonds to a stock-heavy portfolio can smooth out overall returns
Government bond yields serve as a benchmark “risk-free rate” used to price virtually every other financial asset, including mortgages, corporate loans, and stock valuations
The global bond market is enormous — larger than the global stock market by some measures — and its yields are watched closely by central banks and policymakers as a signal of investor expectations for growth and inflation
Retirees and conservative investors often shift toward bonds to preserve capital and generate steady income as they near or enter retirement
Rising or falling bond yields directly influence mortgage rates, so bond market moves affect ordinary households well beyond direct bond investors

Common Pitfalls

Assuming bonds are risk-free: only certain government bonds held to maturity in their home currency are close to risk-free; corporate and long-duration bonds carry real price and default risk
Confusing coupon rate with yield: a bond’s stated coupon only equals its yield when it’s trading exactly at face value; otherwise the two diverge
Ignoring interest rate risk on long-duration bonds: a 30-year bond’s price can swing dramatically with rate changes, far more than a 1-year bond’s
Expecting bond funds to behave like individual bonds: a bond mutual fund or ETF never “matures,” so its price can decline indefinitely if rates keep rising, unlike a single bond that returns to par at maturity if held that long
Overlooking inflation’s effect on real returns: a bond paying 3% when inflation runs at 4% is delivering a negative real return, even though the nominal payment is positive
Chasing yield without checking credit quality: a bond paying an unusually high coupon relative to its peers is usually signaling elevated default risk, not a free lunch

Who Buys Bonds

Individual investors: seeking income, capital preservation, or diversification against stock market swings
Pension funds and insurance companies: matching predictable long-term liabilities (like future pension payouts) with predictable long-term bond income
Central banks: buying or selling government bonds as a tool of monetary policy, including large-scale purchase programs during economic downturns
Mutual funds and ETFs: pooling many investors’ money to buy diversified baskets of bonds, offered as a single fund share (see Mutual Funds and ETFs)
Foreign governments and sovereign wealth funds: holding another country’s government bonds as part of their foreign currency reserves

Example

An investor buys a newly issued 10-year U.S. Treasury bond with a $10,000 face value and a 4% annual coupon, paid semiannually as two $200 payments per year. Over the next decade, the investor collects predictable interest income regardless of stock market swings. If interest rates fall to 3% a few years later, the investor’s bond — still paying the original, now above-market 4% coupon — becomes more valuable and could be sold in the secondary market for more than $10,000. If the investor instead holds it to maturity, they simply receive the final coupon payment plus the full $10,000 principal back, regardless of what happened to its price along the way.

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