XLU vs VPU vs IDU: Utilities ETF Holdings, Overlap and Basket Analysis

A sector label leaves out important rules: which companies may enter, which classification system defines “utilities,” which market-cap bands are eligible, how issuer concentration is limited and how often the index is reweighted. Those decisions can change both the smaller-company tail and the largest positions. XLU and VPU use GICS Utilities, while IDU’s stated benchmark uses ICB’s Utility Industry. The maps are not interchangeable, so equal-language labels do not promise matching constituents.

These are counts of direct-equity rows in the files, not perfectly synchronized counts of index members. XLU’s file also lists cash-like positions and a small utilities futures position; IDU’s CSV includes cash, a money-market fund, collateral and a futures line in addition to equities. The overlap calculation below excludes those rows. The dated files are State Street XLU holdings, Vanguard VPU holdings data, and iShares IDU holdings CSV. Vanguard’s API reports August 31 as the latest complete file located for this review; the product page can surface an older holdings date in its rendered table.

State Street says XLU seeks to track the Utilities Select Sector Index before expenses. The index draws its constituents from S&P 500 companies classified as Utilities under GICS; it does not try to cover every listed U.S. utility or every market-cap tier. S&P’s current U.S. methodology describes the index as capped market-cap weighted and rebalanced quarterly. If a company’s float-adjusted weight is above 24%, the rebalance process caps companies at 23%; it also constrains the combined weight of names above 4.8% to 50%, with buffers and redistribution rules. This is a concentration-control process layered on market capitalization, not equal weighting. See the State Street XLU profile, S&P Utilities Select Sector overview and S&P U.S. Indices Methodology.

The September 24 XLU export contains 31 direct stocks. NextEra Energy (NEE) is 12.72662%; Southern (SO) 7.693124%; Duke Energy (DUK) 7.122851%; Constellation Energy (CEG) 6.954891%; and American Electric Power (AEP) 5.163971%. The five sum to 39.661457%. The top ten sum to 58.760879%, or 58.76% rounded to two decimals. Although the benchmark has buffers intended to control extreme concentration at scheduled checks, weights can move between reviews as prices change. State Street’s September 24 industry table assigns 65.21% to Electric Utilities, 26.16% to Multi-Utilities, 4.38% to Independent Power and Renewable Electricity Producers, 2.14% to Gas Utilities and 2.11% to Water Utilities. That profile is broader than “regulated electric wires” alone.

Vanguard says VPU tracks the MSCI US Investable Market Utilities 25/50 Index. The index covers U.S. large-, mid- and small-cap companies classified in GICS Utilities. The 25/50 constraints limit one group entity to 25% and all group entities individually above 5% to 50% together. The methodology uses an optimization framework to stay close to its parent index while satisfying those limits; the caps do not turn the portfolio into an equal-weight basket. Vanguard describes full replication when possible and sampling when regulatory constraints prevent it. See Vanguard’s VPU profile, the MSCI index profile and MSCI 25/50 methodology.

The latest complete Vanguard API snapshot found for this review is August 31, 2026, with 68 equity rows. Its top weights are NEE 11.73099%, SO 6.77662%, DUK 6.38579%, CEG 5.86491% and AEP 4.55053%; the top five total 35.30884%. The top ten total 52.70344%, or 52.70% rounded. Compared with XLU’s September file, VPU’s larger eligible universe shows up mainly below the shared large-cap core: 37 of VPU’s 68 stocks are absent from XLU’s 31-stock list. This is a wider company-size range, not a promise that small stocks have a large portfolio weight. The source weights are fund weights as reported by Vanguard; they are not recomputed from later market prices.

BlackRock identifies IDU’s benchmark as the Russell 1000 Utilities RIC 22.5/45 Capped Index. FTSE Russell describes it as U.S. large-cap companies assigned to the Utility Industry under ICB. At quarterly index reviews, a single company is capped at 22.5%, while companies individually above 4.5% together cannot exceed 45%. A scheduled cap is an index construction rule, not a guarantee that a fund’s live market weights stay exactly at those levels between reviews. See the iShares IDU profile, FTSE Russell index code sheet and capping methodology guide.

BlackRock’s September 24 CSV has 46 equity rows. NEE is 10.78%, SO 6.52%, DUK 6.03%, CEG 5.73% and Waste Management (WM) 5.29%; the top five total 34.35%, and the top ten total 52.12%. IDU’s issuer exposure breakdown on that date includes 10.27% in Environmental & Facilities Services, alongside electric utilities, multi-utilities, power producers, gas and water utilities. WM, Republic Services, Clean Harbors and GFL Environmental are visible in the direct-equity file. This is a useful reminder to inspect the actual basket and the provider’s industry labels. The breakdown does not establish that every position is a regulated electric, gas or water network company, and its category names should not be compared as if they were the same taxonomy as State Street’s GICS categories.

For XLU–VPU, we matched direct equities by CUSIP, which both files provide. For pairs involving IDU, the BlackRock CSV supplies ticker and issuer name but no CUSIP in this export; we matched exact tickers and manually checked the company names. We excluded cash, money-market funds, collateral and futures. We summed the issuers’ published portfolio weights over the matched names. The final column sums the lower of the two fund weights for each shared name. That lower-weight total is a descriptive common-allocation floor, not an industry-standard overlap statistic, not return correlation and not a forecast of diversification.

The XLU–IDU row is the cleanest same-date comparison: all 31 XLU stock tickers appear in IDU, and those names account for 84.41% of IDU’s equity-fund weight. The remaining 15.36 percentage points of IDU’s direct-equity weight are in stocks absent from XLU’s file. For XLU–VPU and VPU–IDU, the dates differ by more than three weeks. During that gap, prices, shares, index membership and fund flows can change. Their ticker intersections describe the named snapshots, not a synchronized September 24 or August 31 overlap. IDU rounds weights to two decimals in the CSV, so its contributions are less precise than the five- or six-decimal source weights in the other two files. Published values are rounded to two decimals in the table.

Suppose a hypothetical account places US$5,000 in XLU and US$5,000 in IDU. Using both September 24 files, the calculated NEE exposure is US$5,000 × 12.72662% = US$636.33 from XLU, plus US$5,000 × 10.78% = US$539.00 from IDU, for US$1,175.33 of NEE exposure across a US$10,000 account, or about 11.75%. This arithmetic shows how two tickers can repeat a company; it is not a forecast, return calculation or recommendation. Applying the same process across every CUSIP or verified ticker is the right way to add the account’s exposure company by company.

A broad-market fund such as VOO already holds many S&P 500 utilities; a total-market fund such as VTI can also include companies outside the S&P 500. Adding a sector fund therefore often changes the weight of companies already in a broad basket, rather than adding wholly separate businesses. Compare VTI and VOO’s broad-market baskets and the energy-sector ETF basket comparison. Energy and utilities are separate GICS sectors, though some power generators and energy suppliers operate across economic boundaries. Sector labels classify companies; they do not guarantee that two industries hedge each other or move in opposite directions.

The three baskets include companies with different mixes of regulated electricity and gas networks, generation, transmission, water, independent power and environmental services. Their revenues can be affected by the rules and timing of rate cases, capital spending, financing costs, fuel and power prices, weather, plant availability and local demand. FERC says it generally regulates interstate electricity transmission rates, while distribution rates are generally handled by state or local authorities. This division helps explain why utilities do not face one uniform regulatory or earnings path; it does not establish a return prediction. See FERC’s explanation of electric transmission formula rates.

The issuer pages list expense ratios of 0.08% for XLU, 0.09% for VPU and 0.37% for IDU. On a hypothetical balance fixed at US$10,000 for a full year, the simple calculation is US$8, US$9 and US$37. The difference between XLU and VPU is about US$1; IDU is US$29 above XLU and US$28 above VPU. Fund expenses accrue over time against changing assets, so this is an illustration rather than a bill. It excludes bid–ask spreads, brokerage charges, taxes, tracking differences and the consequences of holding several funds with repeated stocks. See the expense ratio versus total cost guide.

Before comparing these tickers, decide whether the intended exposure is the S&P 500 utilities subset, a broader GICS utilities market across company sizes, or the Russell 1000 ICB utility-industry basket. Then compare dated full holdings by security identifier, separate stocks from cash and derivatives, inspect concentration and sector classifications, and check the current prospectus and trading costs. The September 24 XLU–IDU match offers a same-day direct-equity comparison; no same-date VPU file was available in the Vanguard endpoint used here. These figures describe portfolio construction as of the listed dates, not future performance or suitability for a particular investor.