Are Your Bonds Leaking?
In a word: yes. The way coupon-bearing bonds are marketed understates a critical flaw in how their returns actually compound — and most investors have no idea it's happening.
The Yield to Maturity Illusion
When you buy a bond, you're quoted a Yield to Maturity (YTM). This number represents the total return you'll earn if you hold the bond to maturity — combining the purchase price, the maturity value, and the periodic coupon payments you receive along the way.
The problem is what YTM assumes about those coupon payments. The calculation assumes every coupon you receive gets reinvested at the original investment rate. If you buy a 5.3% bond, YTM assumes every $25 semi-annual coupon payment gets reinvested at exactly 5.3%.
Where do you actually invest small, irregular coupon payments at the original investment rate? Nowhere. They go into a money market account, get spent, or sit idle. The compounding assumption that drives the YTM number is almost never realized.
The Real Estate Analogy
Think of it like a rental property. You buy a property for $100,000, receive $1,000 monthly rent for 10 years, then sell for $100,000. YTM-style thinking says your total return is a specific percentage based on all those cash flows combined. But if you spend the rent instead of reinvesting it at the same return rate, your actual performance is materially lower than the stated yield.
Why This Is Getting Worse
In low-rate environments, the reinvestment problem is compounded. There are fewer places to reinvest small coupon payments at rates anywhere near the original bond yield. And when rates rise, existing bond prices decline — so the bond you're holding loses market value at exactly the moment your reinvestment options are theoretically improving.
What YTM Actually Is
YTM is useful for one thing: comparing bonds at the moment of purchase. It's a snapshot, not a guarantee. Using it as the basis for long-term portfolio projections creates a false expectation of compounding that will not materialize. The "leakage" between the projected and actual returns is real money — and over a 20 or 30-year retirement, it adds up to a significant shortfall.