How Long Can Stocks Beat Bonds By A Wide Margin?

 | Jun 21, 2018 08:38AM ET

Stocks are expected to outperform bonds in the long run, but how much is too much over a medium-term horizon?

The question is topical in the wake of a strong bull market for US equities over the past decade. Although stocks have had a rough ride so far in 2018, recent wobbles haven’t dented the decisive performance edge over bonds, at least not yet.

Consider how representative mutual funds stack up over the past 24 years. For stocks, the proxy is Vanguard 500 Index Investor, an index fund that tracks the S&P 500. For bonds, the proxy is Vanguard Interm-Term Invmt-Grade Inv, a portfolio with an average effective maturity of six years that’s comprised of US government securities and investment-grade corporate bonds.

The chart below tracks how the daily return spread for the two funds has fared through time. The spread is calculated as the cumulative daily return difference for stocks less bonds. A rising spread index indicates that stocks are outperforming bonds; a falling index reflects bonds beating stocks. As you can see, recent history has favored stocks – rather dramatically, in fact. The spread index’s current reading is 2.27, as of yesterday’s close (June 20) – close to the highest level in nearly 18 years.