Stock duration is a way to understand how sensitive a stock may be to changes in interest rates. The concept comes from the bond market, where investors face the risk that rates will change after they lend money. Lending $100 at 5% per year is beneficial if prevailing rates go down in the meantime. You still have your money lent at a locked 5%, whereas making a new loan would force you to lend at a lower rate. Conversely, if rates tick higher, you’ve lent at 5% when you could have waited to lend at a higher rate, if you’d had a crystal ball.
So, the longer a bond’s maturity, the greater its sensitivity to interest rates. In other words, locking in a below-market rate for 10 years is more costly than making the same mistake over five years. This is called interest rate risk, and the measurement of a bond’s sensitivity to interest rate risk is called duration.
Stock duration is more nuanced, but the underlying principle is similar. Stock investors buy shares of companies, which entitle them to a share of future profits. If the company is highly profitable today, then the investor is less reliant on the future unfolding in a manner beneficial to the company. Take the consumer staples sector for example. Many mature staples companies generate substantial sales and strong cash flow from established products, even when the long-term growth of the company itself is modest. Investors in these companies are often placing greater value on reliable near-term cash flows than on distant future growth.
Compare consumer staples with the technology sector, where many companies generate little or no profit today but offer the potential for significant earnings in the future. Technology investors are placing greater weight on those future profits. Just as bondholders who lend for longer face greater uncertainty about interest rates, stockholders relying on far-off earnings face greater uncertainty about whether those expectations will be realized. Prevailing interest rates can significantly influence this risk-reward calculation.
We can derive the value of a stock by estimating its future cash flows and discounting (aka adjusting) them back to today’s dollars. This is just an academic way of saying that a business is worth all its future cash flows net of a haircut we apply to account for unknown risks. Higher rates reduce the present value of those future cash flows, while lower rates increase it. The further into the future the cash flows are expected, the greater the effect.
Like long-dated bonds, companies whose values depend heavily on profits far in the future are more exposed to rising rates because those distant cash flows become less valuable when discounted at higher rates. By contrast, companies generating substantial cash today have lower stock duration because investors rely more on near-term cash flows than uncertain future growth. In simple terms, rising rates tend to favor businesses with current cash flows over companies whose investment cases depend primarily on distant future earnings.
Stock duration offers another way to diversify an equity portfolio. Combining shorter-duration companies, whose valuations rely more on current cash flows, with longer-duration companies, whose valuations depend more on future growth, can reduce a portfolio’s reliance on a single interest-rate or economic scenario. Combining both can preserve meaningful growth opportunities while helping to mitigate downside risks during periods of market volatility or changing interest rates.
