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Why Yield to Maturity Exists (and Why Coupon Rate Isn't Enough)
A bond's coupon rate is fixed forever — a 5% coupon bond always pays 5% of face value in annual interest. But the price you pay for that bond in the secondary market changes every day as interest rates move. Pay $1,000 for a 5% bond and you earn exactly 5%. Pay $950 and you earn more than 5% (because you also get a $50 capital gain when the bond matures and returns $1,000). Pay $1,050 and you earn less than 5% (because you'll lose $50 at maturity).
YTM captures all of this in one number. It's the single annualized return that makes your entire cash flow — all coupon payments plus the face value repayment at maturity — equal to today's purchase price in present value terms. If two bonds have different coupons, prices, and maturities, you can still compare them directly by comparing their YTMs.
The Three Yield Measures — and Their Differences
Coupon Rate
The coupon rate is the annual interest the bond pays as a percentage of face value. It's fixed at issuance and never changes. A $1,000 bond with a 5% coupon pays $50/year whether its market price is $800 or $1,200. Coupon rate tells you nothing about the return you'll earn from buying the bond today at today's price.
Current Yield
Current yield = Annual coupon ÷ Current price. It measures your income return based on what you actually paid. Buy the 5% bond at $950 and your current yield is $50 ÷ $950 = 5.26%. It's better than coupon rate for measuring income, but it still ignores the capital gain or loss you'll receive at maturity.
Yield to Maturity
YTM is the discount rate that makes the present value of all future cash flows (coupons + face value repayment) exactly equal to the current price. It's the true total return including income AND capital gain/loss. For the $950 bond with $50/year coupon and 10 years to maturity, the YTM is approximately 5.57% — higher than the 5.26% current yield because it includes the $50 gain at maturity spread across 10 years.
The YTM Approximation Formula
While the exact YTM requires iteration (trial and error), a useful approximation formula gives results accurate to about 0.1%:
Example: $1,000 face value, 5% coupon ($50/year), current price $950, 10 years to maturity:
Capital gain = ($1,000 − $950) ÷ 10 = $5/year
Average price = ($1,000 + $950) ÷ 2 = $975
YTM ≈ ($50 + $5) ÷ $975 = 5.64%
(Exact YTM via bisection: 5.57% — close enough for comparison purposes.)
Discount Bond vs. Premium Bond: How YTM Relates to Coupon Rate
| Bond Price | Name | YTM vs. Coupon Rate | YTM vs. Current Yield |
|---|---|---|---|
| Below face value | Discount bond | YTM > coupon rate | YTM > current yield |
| Equal to face value | Par bond | YTM = coupon rate | YTM = current yield |
| Above face value | Premium bond | YTM < coupon rate | YTM < current yield |
Three Important Limitations of YTM
1. It Assumes You Hold to Maturity
YTM is only realized if you hold the bond until it matures. If you sell before maturity, your actual return depends on the price you sell at — which is determined by interest rates at that time. If rates rise after you buy, you'll sell at a loss. If rates fall, you'll sell at a gain. YTM is most useful as a comparison metric, not as a guaranteed return projection.
2. It Assumes Coupon Reinvestment at YTM
YTM's calculation implicitly assumes you reinvest each coupon payment at the same YTM rate. In practice, you may reinvest at a higher or lower rate depending on what rates are when you receive each payment. This reinvestment risk means your actual realized return can differ from YTM — especially for long-maturity bonds in volatile rate environments.
3. It Doesn't Account for Call Provisions
Many corporate bonds are callable — the issuer can redeem them before maturity at a specified price if interest rates fall. If your bond is called early, you won't receive the remaining coupon payments you'd planned on. For callable bonds, use yield to call (YTC) — calculated the same way as YTM but using the call date and call price instead of the maturity date and face value.
To calculate YTM for any bond, use the Bond Yield Calculator. For an introduction to the broader bond market and bond types, read how bonds work.
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Frequently Asked Questions
What does yield to maturity mean?
YTM is the total annualized return you'd earn by buying a bond at its current price and holding it until maturity, collecting all coupon payments. It's expressed as an annual percentage and accounts for three things: coupon income, any capital gain (bond bought below face value), and any capital loss (bond bought above face value). It's the most complete single measure of a bond's return.
What is the difference between YTM and current yield?
Current yield = annual coupon ÷ current price. It only measures income return. YTM also includes the capital gain or loss at maturity. For a bond bought below face value, YTM is higher than current yield (the capital gain adds to total return). For a bond bought above face value, YTM is lower than current yield (the capital loss subtracts from total return).
Is higher YTM always better?
Higher YTM means higher return — but usually means higher risk. Government bonds have low YTM because they're safe. Investment-grade corporate bonds pay slightly more for their credit risk. High-yield (junk) bonds pay the most but carry significant default risk. When comparing bonds of the same type and maturity, higher YTM is preferable. Across types, higher YTM signals the market is pricing in more risk.
How do I calculate YTM?
The exact calculation requires iterative methods (trial and error to find the discount rate). The approximation formula is: YTM ≈ (Annual Coupon + (Face Value − Price) ÷ Years) ÷ ((Face Value + Price) ÷ 2). This is accurate to about 0.1%–0.2% for most bonds. Use the Bond Yield Calculator above for the exact result via numerical bisection.
Does YTM change over time?
Yes — YTM changes every time the bond's market price changes, which happens continuously. The coupon rate never changes, but YTM fluctuates with market interest rates, the bond's remaining term, and the issuer's credit quality. This is why bond prices are quoted in terms of yield in financial markets — it normalizes bonds with different coupons and prices for apples-to-apples comparison.