Episode 41: Duration

Hey! I'd love to hear your thoughts, send me a voice note.Episode Summary Why do two bond portfolios of identical credit quality and coupon rates experience wildly different price declines when interest rates shift? The answer lies in duration, a single, highly powerful metric that measures how sensitive any bond's price is to interest rate swings. This episode breaks down the dual definitions of duration, the three structural factors that dictate it, and how investors can use this number to match their portfolio to their actual investment horizon.Key ConceptsThe Dual Definition: Duration is simultaneously the mathematical sensitivity of a bond's price to interest rate changes (e.g., a duration of 5 means roughly a 5% price change for every 1% shift in yields) and the weighted average time it takes to get your money back.The Three Drivers: Duration is structurally determined by:Maturity: Longer maturities directly increase duration.Coupon Size: Higher coupons return cash earlier, lowering duration.Yield Levels: The prevailing market yield level itself acts as a minor factor.The Zero-Coupon Peak: Because zero-coupon bonds make no intermediate payments, their duration equals their maturity exactly, making them the most interest-rate-sensitive conventional instruments in existence.The Volatility Gap in NumbersConsider two 5% coupon bonds priced at par ($1,000) when required yields rise by 1% (to 6%):The 3-Year Bond: Price falls to $973.27 (down ~2.7%). Its modified duration is ~2.7.The 20-Year Bond: Price falls to $885.30 (down ~11.5%). Its modified duration is ~12.46.The 20-Year Zero-Coupon Bond: Price falls from $376.89 to $311.80 (down over 17%). Its duration is exactly 20.Practical Portfolio RulesEvery bond fund publishes its duration. To protect your capital, match the fund's duration to your time horizon. A long bond fund is not "conservative"—it simply exchanges credit risk for massive interest rate sensitivity.Disclaimer Educational content only, not financial advice. Speakers are not registered advisors; consult a professional.