Bond prices and yields are two sides of the same coin, and understanding how they interact is essential for any fixed-income investor. In this lesson, you will learn why bond prices move the way they do, how to measure the return a bond offers, and what risks to watch for when adding bonds to your portfolio.
The Price-Yield Inverse Relationship
The single most important concept in bond investing is the inverse relationship between price and yield. When interest rates rise, existing bond prices fall. When interest rates fall, existing bond prices rise. This is not a theory or a tendency - it is a mathematical certainty built into how bonds work.
Why does this happen? Because bonds compete with each other in the marketplace. If new bonds offer higher interest rates, older bonds with lower rates become less attractive. To compensate, their prices must drop until their effective yield matches what new bonds are offering.
Example: How Rising Rates Affect Bond Prices
Imagine you buy a bond with a face value (also called par value) of $1,000 that pays a 4% annual coupon - meaning you receive $40 per year in interest. At the time you buy it, 4% is the going market rate, so you pay exactly $1,000 for the bond.
Six months later, interest rates rise and new bonds are being issued at 5%, paying $50 per year on a $1,000 face value. Now your bond only pays $40 per year. If you wanted to sell your bond, no rational buyer would pay $1,000 for $40 in annual income when they could pay $1,000 for $50 in annual income from a new bond.
To make your bond competitive, its price must drop. Specifically, it would need to fall to approximately $800 so that the $40 coupon payment represents a 5% yield ($40 / $800 = 5%). The exact price depends on the bond's remaining maturity and other factors, but the principle is clear: higher market rates push existing bond prices down.
The reverse is equally true. If market rates dropped to 3%, your 4% bond would become more valuable because it pays more than newly issued bonds. Buyers would be willing to pay a premium above $1,000 to secure that higher income stream.
Current Yield
The simplest way to measure a bond's return is the current yield. It tells you what percentage return you are earning based on the bond's current market price, not its face value.
The formula is straightforward:
Current Yield = Annual Coupon Payment / Current Market Price
Example: Calculating Current Yield
A bond has a face value of $1,000, a coupon rate of 6% (paying $60 per year), and is currently trading at $950 in the secondary market.
Current Yield = $60 / $950 = 6.32%
Notice the current yield (6.32%) is higher than the coupon rate (6%) because you are buying the bond at a discount. You are paying less than face value but still receiving the same $60 annual payment.
If that same bond were trading at $1,100, the current yield would be $60 / $1,100 = 5.45%, which is lower than the coupon rate because you are paying a premium for the bond. Current yield is easy to calculate, but it has a limitation: it ignores any gain or loss you will experience when the bond matures at its face value.
Yield to Maturity (YTM)
Yield to maturity (YTM) is a more comprehensive measure of a bond's total expected return. It accounts for three components: the annual coupon payments you receive, the difference between the price you paid and the face value you will receive at maturity, and the time remaining until the bond matures.
Think of YTM as the bond's internal rate of return - the annualized rate that would make the present value of all future cash flows (coupons plus face value at maturity) equal to the bond's current price. It is the most widely used metric for comparing bonds.
Example: Why YTM Matters
Consider a bond with a face value of $1,000, a 5% coupon rate ($50/year), 10 years to maturity, and a current price of $920. The current yield is $50 / $920 = 5.43%. But the YTM is higher - approximately 5.95% - because it also accounts for the $80 gain you will earn when the bond matures at $1,000 (you paid $920). That $80 gain, spread over 10 years, adds roughly 0.52% annually to your total return.
Conversely, if the bond were priced at $1,080, the YTM would be lower than the current yield because you would lose $80 at maturity when you only receive $1,000 back for a bond you paid $1,080 for.
Premium vs Discount Bonds
Bonds trade at different prices relative to their face value depending on how their coupon rate compares to current market interest rates. Understanding these categories helps you quickly assess what a bond's price is telling you.
Premium Bonds
A bond trades at a premium (above par) when its coupon rate is higher than the current market interest rate. Investors are willing to pay more than face value to secure the higher-than-market income stream. For example, a bond paying 6% when the market rate is 4% will trade well above $1,000. As the bond approaches maturity, its price gradually declines toward $1,000 - a process called amortization of premium.
Discount Bonds
A bond trades at a discount (below par) when its coupon rate is lower than the current market interest rate. The lower income makes the bond less attractive, so its price drops to compensate. A bond paying 3% when the market rate is 5% will trade below $1,000. As maturity approaches, the price gradually rises toward $1,000 - this is called accretion of discount.
Par Bonds
A bond trades at par when its coupon rate equals the current market interest rate. The bond is priced at exactly its face value because its income stream matches what the market demands.
Quick Reference: Bond Pricing Summary
| Condition | Price vs Par | YTM vs Coupon |
|---|---|---|
| Coupon > Market Rate | Premium (above $1,000) | YTM < Coupon Rate |
| Coupon = Market Rate | Par ($1,000) | YTM = Coupon Rate |
| Coupon < Market Rate | Discount (below $1,000) | YTM > Coupon Rate |
Interest Rate Risk
Interest rate risk is the risk that changes in market interest rates will cause a bond's price to fluctuate. All bonds face this risk, but some are far more sensitive than others. The key factor is maturity: the longer the time until a bond matures, the more its price will move in response to interest rate changes.
Why does maturity matter so much? A bond with 30 years remaining locks you into a fixed coupon rate for three decades. If rates rise, you are stuck earning below-market income for a very long time. A bond with only 2 years left will return your principal soon, so the impact of rate changes is minimal - you will get your money back quickly and can reinvest at the new, higher rate.
Example: Maturity and Price Sensitivity
Suppose interest rates rise by 1% across the board. Here is the approximate impact on bonds with different maturities, all starting with a 4% coupon:
| Bond Maturity | Approximate Price Change |
|---|---|
| 2-Year | -1.9% |
| 10-Year | -8.1% |
| 30-Year | -17.2% |
A 1% rate increase causes a 30-year bond to lose roughly nine times as much value as a 2-year bond. This illustrates why maturity is the primary driver of interest rate risk.
Bond investors often use a concept called duration to measure interest rate sensitivity more precisely. Duration, measured in years, estimates how much a bond's price will change for a 1% change in interest rates. A bond with a duration of 7 years will drop approximately 7% in price if interest rates rise by 1%, and gain approximately 7% if rates fall by 1%.
Duration takes into account not just maturity but also the coupon rate and current yield. Higher coupon bonds have shorter durations (and less rate sensitivity) because more of their cash flows come sooner. Zero-coupon bonds have the longest duration for any given maturity because all of their return comes at maturity.
Credit Risk
While interest rate risk affects all bonds, credit risk (also called default risk) varies dramatically from one bond issuer to another. Credit risk is the possibility that the bond issuer will fail to make interest payments or repay the principal at maturity. The higher the credit risk, the higher the yield investors demand as compensation.
Credit Rating Agencies
Three major agencies assess the creditworthiness of bond issuers: Moody's, Standard & Poor's (S&P), and Fitch. Each uses a letter-grade system to rank bonds from the safest to the most speculative.
Credit Rating Scale (Simplified)
| S&P / Fitch | Moody's | Category |
|---|---|---|
| AAA | Aaa | Highest quality |
| AA | Aa | High quality |
| A | A | Upper medium quality |
| BBB | Baa | Medium quality (lowest investment grade) |
| BB | Ba | Speculative (high-yield) |
| B | B | Highly speculative |
| CCC and below | Caa and below | Substantial risk / near default |
Investment Grade vs High-Yield
The dividing line falls at BBB-/Baa3. Bonds rated BBB- (S&P/Fitch) or Baa3 (Moody's) and above are considered investment grade. These issuers have a strong ability to meet their financial obligations, and their bonds are considered relatively safe.
Bonds rated below that threshold are called high-yield bonds (also known as "junk bonds"). These carry a higher risk of default, so issuers must offer significantly higher yields to attract investors. High-yield bonds can offer returns of 6-10% or more, but they come with real risk - during economic downturns, default rates on high-yield bonds can spike dramatically.
Credit Spreads
The extra yield a bond pays above a comparable U.S. Treasury bond is called the credit spread (or yield spread). Since Treasuries are considered virtually risk-free (backed by the U.S. government), the spread represents the additional compensation investors demand for taking on the issuer's credit risk.
Example: Understanding Credit Spreads
A 10-year U.S. Treasury bond yields 4.0%. A 10-year corporate bond rated A yields 4.8%. The credit spread is 0.8% (or 80 basis points). This means investors require an extra 0.8% per year to compensate for the risk that the corporation might default.
A 10-year BB-rated corporate bond might yield 6.5%, giving it a credit spread of 2.5% (250 basis points) over Treasuries. The wider spread reflects the higher probability of default.
Credit spreads widen during periods of economic uncertainty (investors demand more compensation for risk) and narrow during periods of economic confidence.
Key Takeaways
- Bond prices and yields move in opposite directions - this is the fundamental law of bond investing.
- Current yield measures income relative to market price, while yield to maturity captures total return including price gains or losses at maturity.
- Bonds trade at a premium when their coupon exceeds market rates, at a discount when their coupon is below market rates, and at par when they match.
- Longer-maturity bonds are more sensitive to interest rate changes. Duration quantifies this sensitivity.
- Credit ratings from Moody's, S&P, and Fitch help assess the likelihood of default. Investment-grade bonds (BBB/Baa and above) are considered relatively safe.
- Credit spreads over Treasuries represent the extra yield investors demand for taking on default risk.
- High-yield (junk) bonds offer higher returns but carry meaningfully higher default risk, especially during economic downturns.
Disclaimer: This content is for educational purposes only and does not constitute financial advice. Always do your own research and consider consulting a qualified financial advisor before making investment decisions.