A Case Study in Mismatched Fund Returns
Why do a fund's returns sometimes differ from its underlying index? A longstanding legal principle holds the key.
Over the past 12 months, the Technology Select Sector SPDR Fund (XLK) – a member of the Kiplinger ETF 20, our favorite exchange-traded funds – has returned a loss of 10.5%, lagging a 5.0% loss in the S&P 500 Information Technology Index.
Both the ETF and the index are weighted by market value and include the same companies – the 69 tech stocks that are members of the S&P 500 stock index. So, what gives?
Weighting matters when it comes to fund returns
The weighting of stocks in the ETF varies from their weighting in the index, thanks to a rule in the Investment Company Act, enacted in 1940, that governs how mutual funds and ETFs should maintain diversification.
From just $107.88 $24.99 for Kiplinger Personal Finance
Be a smarter, better informed investor.
Sign up for Kiplinger’s Free Newsletters
Profit and prosper with the best of expert advice on investing, taxes, retirement, personal finance and more - straight to your e-mail.
Profit and prosper with the best of expert advice - straight to your e-mail.
"The index doesn't have to adhere to the 1940 Investment Company Act, but the fund does," says Matthew Bartolini, head of ETF research in the Americas for State Street Global Advisors.
The diversification rules are designed to avoid risk from stock concentration in funds.
Chiefly, the rules prescribe that no single stock can make up more than 25% of any given fund's assets and that the sum of any stocks in the fund with a 5% or greater stake must add up to less than 50%.
Ergo, Apple (AAPL), Microsoft (MSFT) and Nvidia (NVDA) – top holdings in both the Technology Select Sector ETF and the Information Technology index – make up 41% of the ETF but account for roughly 60% of the Info Tech index.
The variation in the weighting of holdings had little impact on relative returns in 2022 and 2023, when the ETF and the Info Tech index posted similar gains.
But 2024 was different, thanks to mega-size gains in a handful of mega-size companies. The ETF logged a 21.6% gain that calendar year; the Info Tech index, 36.6%.
"It has been an anomalous market," says Bartolini. Of course, many of those mega-size firms have given back some of those gains recently, and that may mean the ETF will close the gap in relative performance.
The Technology Select Sector SPDR is a solid tech fund. The ETF's 10-year 17.4% annualized return beat 89% of its peers.
This item first appeared in Kiplinger Personal Finance Magazine, a monthly, trustworthy source of advice and guidance. Subscribe to help you make more money and keep more of the money you make here.
Related Content
Profit and prosper with the best of Kiplinger's advice on investing, taxes, retirement, personal finance and much more. Delivered daily. Enter your email in the box and click Sign Me Up.

Nellie joined Kiplinger in August 2011 after a seven-year stint in Hong Kong. There, she worked for the Wall Street Journal Asia, where as lifestyle editor, she launched and edited Scene Asia, an online guide to food, wine, entertainment and the arts in Asia. Prior to that, she was an editor at Weekend Journal, the Friday lifestyle section of the Wall Street Journal Asia. Kiplinger isn't Nellie's first foray into personal finance: She has also worked at SmartMoney (rising from fact-checker to senior writer), and she was a senior editor at Money.
-
Gen X Turns 60: It's Time to Remix Your Retirement PlaylistIf you want a worry-free retirement, you can't keep playing the same old song. You need to freshen up your financial strategies, as well as your music.
-
I'm a Financial Adviser: Here's How a Three-Part Retirement 'Crash Plan' Can Prepare You for Market TurbulenceHaving a plan ready to go when markets get wild — covering how you'll handle income, rebalancing and taxes — can be the ultimate retirement secret weapon.
-
Investors Buy the Nasdaq's Big Dip: Stock Market TodayStocks are up and down again to end an up-and-down week ahead of big earnings announcements and the eventual return of regular economic data flow.
-
Here's How to Plan This Year's Roth Conversion, From a Wealth ManagerWhile time is running out to make Roth conversions before the end of the taxable year, consider taking your time and developing a long-term strategy.
-
Four Times You Need a Second Opinion on Your Financial PlanIs your financial plan fit for purpose — or is your adviser peddling an outdated strategy? When you see these red flags, it's time for a second opinion.Evan
-
'But It's Not My Fault!': Your Insurance Company Absolutely Will Blame You in These Five ScenariosInsurance companies care about 'fault' in more ways than you think — from payment mishaps to your neighbor's landscaping — so it's on you to manage the risks.
-
Dow Dives 797 Points as Government Opens: Stock Market TodayThe process of pricing and re-pricing realities old and new never stops, and next week promises to be at least as exciting as this week.
-
5 Core Stocks Every Investor Should Own In 2026 and BeyondCore stocks are solid, long-term investments that provide stable returns and steady growth within your portfolio. Here are five we like.

