Treasury bonds are the benchmark against which all other fixed-income investments are measured — the risk-free rate that anchors every financial model and the safety anchor that protects portfolios when equity markets collapse. Understanding how to calculate Treasury bond yields, compare them to alternatives, and determine when they belong in a portfolio requires grasping the fundamental relationship between bond prices and yields — a relationship that confuses more investors than almost any other fixed-income concept.
I Bonds: Series I Savings Bonds
Series I Savings Bonds are non-marketable Treasury securities (you can't sell them in the secondary market) that pay an inflation-adjusted composite rate combining a fixed base rate and a variable component tied to CPI. The composite rate adjusts every 6 months in May and November. I Bonds bought when inflation is high can deliver compelling short-term yields — in November 2022, the composite rate reached 6.89% — though rates have since normalized with declining inflation.
Purchase limits: $10,000 per person per calendar year in electronic form through TreasuryDirect, plus $5,000 in paper form using your tax refund. Must hold for at least 12 months; selling within 5 years forfeits the last 3 months of interest. Tax treatment: federal taxable but state-tax-exempt; can also defer federal tax until redemption or use for qualified education expenses federal-tax-free. These features make I Bonds competitive with high-yield savings accounts and CDs for conservative savers who can lock up the funds for at least one year.
Treasury Bonds in Portfolio Construction
In a balanced portfolio, Treasury bonds serve two distinct purposes: income generation and equity offset (Treasuries typically rise when equity markets fall, providing rebalancing opportunities and psychological stability during market downturns). The equity offset function requires long-duration Treasuries — short-term T-bills don't provide the same crisis protection because they don't rally significantly when stocks fall.
The appropriate Treasury allocation depends on time horizon, risk tolerance, and whether you need current income. For a 20-year investment horizon, the bond allocation is primarily about volatility reduction and rebalancing fuel — not return generation. For a 5-year horizon with a specific spending goal, Treasuries provide principal protection and predictable cash flows that equities can't. Laddering maturities — holding bonds maturing in 1, 3, 5, 7, and 10 years — provides both current income and the flexibility to reinvest at prevailing rates as each rung matures, without the price volatility of all-long-duration exposure.
How Treasury Bonds Are Structured
The US Treasury issues securities across a spectrum of maturities: Treasury bills (T-bills) mature in 4, 8, 13, 17, 26, or 52 weeks. Treasury notes mature in 2, 3, 5, 7, or 10 years. Treasury bonds (technically) mature in 20 or 30 years. All are backed by the full faith and credit of the US government — the lowest credit risk available in US dollar-denominated investments.
T-bills don't pay periodic interest; they're issued at a discount and mature at face value. A 26-week T-bill with a face value of $10,000 purchased at $9,740 returns $260 at maturity. Treasury notes and bonds pay a fixed coupon rate semiannually — a 10-year note with a $10,000 face value and 4.5% coupon pays $225 every six months ($450 per year) for 10 years, then returns the $10,000 principal. The coupon rate is fixed at issuance; what changes in the secondary market is the price, which inversely affects yield.
Yield Calculations: Current Yield vs Yield to Maturity
Current yield is the simplest calculation: Annual coupon payment ÷ Current price. A bond with a $500 annual coupon trading at $9,600: current yield = $500 ÷ $9,600 = 5.21%. This tells you the income return based on today's price but ignores the capital gain or loss at maturity.
Yield to maturity (YTM) is the comprehensive measure — the total annualized return if you buy the bond today and hold it to maturity, including all coupon payments and the difference between purchase price and face value. YTM is harder to calculate by hand (it requires solving for the discount rate that equates all future cash flows to the current price) but financial calculators and tools compute it directly. For a bond paying $450 annually, maturing in 8 years, with face value $10,000, currently priced at $9,250: YTM ≈ 5.87% per year. This is more useful than current yield because it captures the $750 capital gain you earn by buying below par and receiving full par at maturity.
Related Calculators
The Price-Yield Relationship
Here's what trips up most bond investors: bond prices and yields move in opposite directions. When market interest rates rise, existing bonds (with their fixed coupons) become less attractive relative to new bonds offering higher coupons — so existing bond prices fall until their yield matches the new market rate. When rates fall, existing bonds with higher coupons become more valuable — prices rise.
Jennifer, 48, in Boston, Massachusetts bought a 10-year Treasury note at par ($10,000) with a 3.5% coupon in early 2021. By late 2022, 10-year Treasury yields had risen to 4.2%. Her bond's market price fell to approximately $9,440 — a $560 loss if she sells. But if she holds to maturity, she receives all coupons plus full $10,000 face value. Her choice: realize the loss now (useful if she can buy higher-yielding bonds and recoup the difference) or hold and earn the original 3.5% she locked in. Duration — a measure of a bond's price sensitivity to interest rate changes — tells you how much a bond's price will change for each 1% change in interest rates. A 10-year bond has a duration of approximately 8 to 9 years, meaning a 1% rate increase reduces its price by roughly 8 to 9%.
TIPS: Treasury Inflation-Protected Securities
TIPS adjust their principal value with CPI inflation. If you buy $10,000 in TIPS and inflation runs 4% over the year, your principal adjusts to $10,400, and your coupon payment is calculated on the new higher principal. This inflation adjustment protects purchasing power in a way conventional bonds don't.
The break-even inflation rate is the CPI rate at which TIPS and conventional Treasuries produce identical returns. If a 10-year Treasury yields 4.5% and a 10-year TIPS yields 1.8%, the break-even inflation rate is 4.5% - 1.8% = 2.7%. If actual inflation exceeds 2.7% over 10 years, TIPS win. If it's below 2.7%, conventional Treasuries win. Comparing to the Fed's 2% inflation target and your own inflation expectations tells you which is the better bet for your specific situation.
