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Repair common Windows errors and clear accumulated junk for a smoother, more stable PC - no reinstall needed.Free scan · no reinstallThe S&P 500 and Wilshire 4500 target different parts of the U.S. stock market, so funds tracking them are generally not substitutes. The S&P 500 is a large-company benchmark; the Wilshire 4500 Completion Index represents mid-, small-, and micro-cap stocks outside the S&P 500. A portfolio can use them for distinct roles, but the index label alone does not tell you which fund is better or whether it is available in your retirement plan.
What each index covers
S&P 500: large-cap stocks
The S&P 500 includes leading U.S. companies and covers approximately 80% of available market capitalization, according to S&P Dow Jones Indices. The index page reported 503 constituents as of August 31, 2026. The “500” in its name is not an exact, fixed count of securities.
Wilshire 4500: completion-market stocks
The Wilshire 4500 Completion Index is defined as the Wilshire 5000 Total Market Index with S&P 500 securities removed. It measures the remaining mid-, small-, and micro-cap segment. Wilshire’s factsheet, dated March 28, 2024, listed 2,884 components and notes that the number varies; “4500” should not be read as a current exact count. The index was created on December 31, 1983. See the Wilshire 4500 Completion Index factsheet.
Are these funds alternatives or complements?
They are different exposures, not two versions of the same market slice. A fund tracking the S&P 500 holds large-cap exposure. A fund tracking the Wilshire 4500 adds stocks excluded from that benchmark, spanning mid-, small-, and micro-cap companies. Used together, they can represent large-cap and completion-market portions of a U.S. stock allocation; the right mix depends on an investor’s overall portfolio and goals.
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Do not assume that a fund called “extended market,” “completion,” or “total market” tracks the Wilshire 4500. Those labels can refer to other benchmarks. Check the fund prospectus for the exact index it seeks to track.
How to compare funds tracking them
An index itself cannot be purchased. Investors gain exposure through a mutual fund or ETF that seeks to track it. The SEC explains this distinction in its Investor.gov guide to index funds.
- Benchmark: Confirm the precise index in the prospectus. Similar-sounding completion or extended-market funds may track a different index.
- Costs: Compare each fund’s current expense ratio and consider trading costs. No matched, current expense figures for Wilshire 4500 and S&P 500 trackers are established here.
- Tracking: Review how closely the fund has followed its benchmark over comparable periods. Sampling, fees, expenses, and trading can cause fund returns to differ from index returns.
- Implementation: Check whether the fund uses full replication or sampling, along with its share class and availability through your brokerage or employer plan.
- Dates: Treat constituent counts, market-coverage figures, returns, and sector weights as dated measurements, not timeless characteristics.
Understand the Wilshire naming
Wilshire announced a modernization and rebranding of its broad Wilshire 5000 series as the FT Wilshire 5000 series in 2021. Its current index-family page lists FT Wilshire 4500, while the March 2024 completion factsheet defines the legacy Wilshire 4500 in relation to the Wilshire 5000 Total Market Index. The family’s naming and a fund’s chosen benchmark may differ, so rely on the benchmark and methodology stated in the fund’s current prospectus. See Wilshire’s 2021 announcement and FT Wilshire index family page.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What the available figures do—and do not—show
The S&P 500’s approximately 80% market-cap coverage and 503 constituents are figures from the S&P Dow Jones Indices page as of August 31, 2026. Wilshire’s 2,884-component figure comes from a factsheet dated March 28, 2024. Because the counts have different dates and measure different indexes, they are not a like-for-like comparison of current market size. Nor do they establish which fund performed better: no matched return period, share classes, or comparable current expense figures are provided.
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