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
Become a smarter, better informed investor. Subscribe from just $107.88 $24.99, plus get up to 4 Special Issues
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.
-
December Fed Meeting: Live Updates and CommentaryThe December Fed meeting is one of the last key economic events of 2025, with Wall Street closely watching what Chair Powell & Co. will do about interest rates.
-
This Is Why Investors Shouldn't Romanticize BitcoinInvestors should treat bitcoin as the high-risk asset it is. A look at the data indicates a small portfolio allocation for most investors would be the safest.
-
I'm a Federal Benefits Pro: I Answer These 2 Questions a LotMany federal employees ask about rolling a TSP into an IRA and parsing options for survivor benefits, both especially critical topics.
-
December Fed Meeting: Live Updates and CommentaryThe December Fed meeting is one of the last key economic events of 2025, with Wall Street closely watching what Chair Powell & Co. will do about interest rates.
-
Why Investors Shouldn't Romanticize Bitcoin, From a Financial PlannerInvestors should treat bitcoin as the high-risk asset it is. A look at the data indicates a small portfolio allocation for most investors would be the safest.
-
I'm a Financial Pro Focused on Federal Benefits: These Are the 2 Questions I Answer a LotMany federal employees ask about rolling a TSP into an IRA and parsing options for survivor benefits, both especially critical topics.
-
Private Credit Can Be a Resilient Income Strategy for a Volatile Market: A Guide for Financial AdvisersAdvisers are increasingly turning to private credit such as asset-based and real estate lending for elevated yields and protection backed by tangible assets.
-
5 RMD Mistakes That Could Cost You Big-Time: Even Seasoned Retirees Slip UpThe five biggest RMD mistakes retirees make show that tax-smart retirement planning should start well before you hit the age your first RMD is due.
-
I'm a Wealth Adviser: My 4 Guiding Principles Could Help You Plan for Retirement Whether You Have $10,000 or $10 MillionRegardless of your net worth, you deserve a detailed retirement plan backed by a solid understanding of your finances.
-
A Retirement Triple Play: These 3 Tax Breaks Could Lower Your 2026 BillGood news for older taxpayers: Standard deductions are higher, there's a temporary 'bonus deduction' for older folks, and income thresholds have been raised.
-
If You're Retired or Soon-to-Be Retired, You Won't Want to Miss Out on These 3 OBBB Tax BreaksThe OBBB offers some tax advantages that are particularly beneficial for retirees and near-retirees. But they're available for only a limited time.