A lot of investors have gotten comfortable with a simple plan: put everything in the S&P 500 and let it ride. And for good reason, large caps have dominated for most of the last two decades.
But the chart below is a good reminder of why that approach has a blind spot.
Since 2005, U.S. small caps have trailed large caps in 14 of the past 21 first halves, including brutal stretches in 2020 (-10.0%) and 2024 (-13.5%). If you only owned the S&P 500, small caps probably weren't even on your radar.
Then 2026 happened. Small caps outperformed large caps by 12.3% in the first half, the strongest reading in this entire dataset.
The Point Isn't That Small Caps Will Win
Nobody knows which asset class leads next, and the data actually backs that up. Looking back at prior years when small caps had a strong first half, large caps often came right back and reclaimed leadership afterward. This time could be no different.
That's exactly why we stay diversified across market caps instead of concentrating in one. Diversification isn't about predicting the next rotation. It's about being positioned to capture it whenever it happens, without having to guess the timing.
Why This Rotation Might Have Legs
A few things make the current small cap move worth watching:
- Valuations are stretched thin. Small caps have been trading cheap relative to large caps for years, so there's more room for prices to grow from here.
- AI isn't just a mega cap story. As AI tools become more accessible, smaller businesses can use them to cut costs and run more efficiently, the same advantage that's fueled large cap earnings growth.
- A cheap starting point plus a real catalyst is often how new cycles begin.
None of this guarantees small caps keep outperforming. But it's a reasonable case for why this rotation could have more room to run, and another reason not to bet the whole portfolio on one part of the market.
The Takeaway
Markets move in cycles, and leadership changes hands more often than most investors expect. Staying diversified across market caps means you don't have to correctly call the next shift to benefit from it, you're already there when it happens.