Skip to navigationSkip to main contentSkip to right columnADVERTISEMENTTrefis TeamFri, June 26, 2026 at 10:04 PM GMT+2 3 min readPhoto by ArtsyBee on PixabayYour small-cap ETF had a great year, but a surprisingly small number of its holdings did the heavy lifting.The iShares Russell 2000 ETF (IWM) delivered a +42.1% return over the past year, but that gain wasn't earned evenly. In fact, the five biggest contributors produced about 55% of the combined gains from the holdings measured, showing how a few key stocks can power a fund that looks broadly diversified on paper.When you own an index fund, you own the math. And the math of the past year shows that your return was disproportionately influenced by a handful of standout performers.The Engine Room: A Holding Did The Work Of ManyThe single biggest contributor to the fund's return was Bloom Energy (BE). While it makes up just 1.8% of the fund, the stock returned stunningly over 1,000% the past year. A performance like that from even a small holding can have an outsized impact on