If you have a piece of your portfolio parked in a standard S&P 500 index fund, you are likely feeling good about the 12% return you have racked up this year. But there is a less flashy corner of the indexing world that has quietly left that performance in the dust. The Invesco S&P 500 Equal Weight ETF (RSP) treats Nvidia, a mid-cap industrial stock, and every other company in the index as equals. That approach has delivered a year-to-date return of 15.95% through August 26, versus the 12.37% posted by the iShares Core S&P 500 ETF (IVV). The gap of nearly 3.6 percentage points has put equal weighting back in the spotlight and pushed RSP to a milestone: on August 19, the fund crossed $100 billion in assets under management for the first time, after pulling in more than $12 billion in net inflows just this year.

The structural difference between the two fund types explains the divergence. A market-cap-weighted fund like IVV gives its largest constituents—Nvidia, Microsoft, Apple, and Amazon—outsized influence because they represent a huge share of the index. RSP, by contrast, assigns each of the 500 companies roughly the same weight at each quarterly rebalance, muting the impact of any single giant. That nuance matters a great deal in 2026, according to Brendan McCann, a senior associate manager research analyst at Morningstar. He points to the underperformance of several big-name tech stocks as the key swing factor. "Several of the big names in the market, like Microsoft, Nvidia, and Apple, have underperformed the broader technology market," McCann explained. "Since RSP underweights those companies, its performance is more insulated when those stocks underperform."

The flip side of the coin has also reinforced the trend. Many smaller S&P 500 stocks have performed exceptionally well in 2026, and equal weighting gives those names more room to drive returns. "Several smaller S&P 500 stocks have performed exceptionally in 2026, and equal weighting gives those stocks more weight," McCann said. So RSP is not just avoiding tech's laggards—it is capturing upside from smaller companies that a cap-weighted fund would barely register.

This milestone naturally raises the question of whether the equal-weight trade has become too popular for its own good. McCann is not worried yet. "I think at $100 billion the ETF still has plenty of runway," he said. However, he flagged a very real constraint tied to fund size: liquidity in RSP's smallest holdings. As the fund's assets grow, it becomes harder to trade the smallest stocks in the portfolio. "There's no perfect number for how large the assets could grow, but I would say if assets were to quadruple, it could be more challenging to rebalance the portfolio," McCann noted. That would put the potential stress point near $400 billion.

McCann sees the current performance gap as a live snapshot of just how much the S&P 500 now depends on a handful of giant stocks. The primary driver, especially given the concentration in today's market, is the performance of the largest stocks relative to the broader market. Because so many of those largest stocks sit in one sector, technology's fortunes disproportionately steer the cap-weighted index's returns. The numbers illustrate how lopsided that concentration has become. As of August 25, the S&P 500 Equal Weight Index held roughly 17% in technology, versus a 38% technology weighting in the standard S&P 500 Index—a gap of about 21 percentage points, according to McCann. The cap-weighted benchmark tracked by most index funds and 401(k) target-date funds is, in effect, a leveraged bet on one sector.

The implication cuts both ways. "Should the technology sector take a hit, RSP should hold up better than the broader market," McCann said, which is a defensive case for equal weighting. But it also means RSP's fortunes will keep hinging on tech's next move: a rebound in Nvidia, Microsoft, or Apple could just as easily narrow the performance gap that has fueled this year's inflows.