# ETF Research Center vs ETF Insider: two funds, or the whole portfolio Both answer how much your funds overlap, for free. One compares two ETFs at a time; the other rolls up a portfolio, mutual funds too, on quarter-old holdings. *https://stockmarketstack.com/compare/etf-research-center-vs-etf-insider* - https://stockmarketstack.com/tools/etf-research-center.md - https://stockmarketstack.com/tools/etf-insider.md Both cards above exist to answer a question an index investor asks late: how much of the same stocks do I already own through the funds I hold. Both answer it free. The difference is the shape of the question each one takes — two funds against each other, or every holding at once — and which funds each will accept at all. ## Two funds, or all of them [ETF Research Center](https://stockmarketstack.com/tools/etf-research-center)'s Fund Overlap tool takes **two** equity ETFs. For each stock both hold, it takes the smaller of the two weights and adds them up; it also prints the number of shared names, what share of each fund's holdings appears in the other, the sector drift between them and the largest over- and underweights. Every fund page also lists its ten closest comparables by overlap. It answers "do these two do the same job" precisely. [ETF Insider](https://stockmarketstack.com/tools/etf-insider) takes **a portfolio**: ETFs, mutual funds and single stocks, added by symbol or by a two-column CSV of symbol and quantity. It draws an overlap matrix for every pair at once, and — the part the other tool does not do — rolls the whole portfolio down to the securities underneath, so it can say how much of your total is in one company, one sector or one country through all your funds together. Its card does not record how the overlap figure is calculated; ETF Research Center's does. The practical difference grows with the number of funds. Five funds are ten pairs, and ten pairwise overlaps still do not add up to "how much of my money is in the largest five stocks" — the overlap between two funds says nothing about a third. If that total is the question, only one of these tools answers it directly. ## Which funds each one will take This settles it for many readers before anything else does. - **Mutual funds** — a 401(k) line-up, say — go into ETF Insider and not into ETF Research Center's overlap tool, which is equity ETFs only. - **UCITS and Canadian funds** go into ETF Research Center, whose universes cover US-listed, Canadian-listed and UCITS funds, London listings included. ETF Insider is US-listed only, takes symbols rather than ISINs, and counts a foreign issuer's fund only if it trades on a US exchange. - **Bond ETFs** are out of scope for ETF Research Center's overlap tool. ETF Insider's card does not exclude them, and does not describe them either. ## How old the holdings are ETF Insider's own FAQ says most of its holdings come from SEC filings and can only be refreshed as funds file each quarter — and those quarter-end portfolios are published up to 60 days late. So an overlap or concentration figure can describe the portfolio as it stood several months earlier. For a broad index fund, whose constituents move slowly, that matters less; for an actively managed or thematic fund, the list may have turned over since. ETF Research Center's card records performance and valuation as end-of-day and complete holdings for select issuers' funds, but not the as-of date of the holdings behind the overlap tool. Read the date beside the result rather than assuming it is current. That the two cards are silent in different places is itself worth knowing: neither is a live view of what a fund holds today. ## What each one adds, and what to ignore ETF Research Center's other free tool on the same question is the **TCO comparison**: two funds side by side on expense ratio, average bid/ask spread and round-trip commission over a holding period you choose. If two funds overlap almost entirely, cost is usually what is left to decide on, and this is the comparison most screeners never make. Its fund pages also print the ALTAR Score and a five-step label from Speculative to Avoid, plus a sell-side price target. Those are a valuation model's forecasts, not facts about the fund, and nothing about overlap depends on them. ETF Insider adds a correlation matrix and an efficient-frontier chart. The second is an optimisation over past returns: it shows which mix would have had the best risk-adjusted result over the history in the tool, not which will. Its site is also hard to date — a 2023 copyright and blog entries ending in January 2025 — though its application was answering searches on 7 October 2026. Neither has an API on the plans an individual would buy, and [Trackinsight](https://stockmarketstack.com/tools/trackinsight), the other free global ETF site in the category, keeps holding overlap for its institutional product. ## The recommendation **Two funds, and the question is whether to keep both** — two S&P 500 trackers, a growth fund against a total-market fund, a UCITS fund against its US twin — use **ETF Research Center** with a free Basic login. Its pairwise overlap is by weight, it works from either fund's side, and the cost comparison on the same site answers what the overlap leaves open. **Three or more holdings, and the question is where the whole portfolio is concentrated** — especially if mutual funds or single stocks are among them — use **ETF Insider**'s free plan, and read every figure as of the last quarterly filing rather than today. Outside US listings it cannot help, and the pairwise tool is the only one of the two that can. Neither question needs a paid plan. Pay ETF Research Center when you want the fundamentals rolled up per fund, and ETF Insider when four saved portfolios or the limited holdings data run out. The rest of the category is on the [ETF research](https://stockmarketstack.com/categories/etf-research) page. ## FAQ ### Which one tells me how much of my portfolio is in a single stock across all my funds? ETF Insider. Its concentration view rolls every fund you add down to the securities underneath and totals them by name, sector, geography and size. ETF Research Center answers the question two funds at a time, or the other way round — its Stock Locator lists every ETF holding a given stock and at what weight — so the portfolio-wide total is arithmetic you would do yourself. ### Can I check the overlap of mutual funds in my 401(k)? With ETF Insider, which takes US-listed mutual funds as well as ETFs and single stocks. ETF Research Center's overlap tool is limited to equity ETFs. Either way the holdings behind a mutual fund come from its periodic filings, so read the result as of the last filing date rather than today. ### Do I need to pay for either to check overlap? No. ETF Research Center's overlap tool shows full results with a free Basic login — anonymous visitors see only the top five rows. ETF Insider's free plan keeps up to four saved portfolios with the overlap and concentration views. The paid plans buy other things — fundamentals and complete holdings on ETF Research Center at $29 a month, unlimited portfolios and Excel export on ETF Insider at $14 a month or $99 a year. ### Why does the overlap percentage change depending on which fund I start from? Because shared holdings are a different share of each fund. On 7 October 2026 ETF Research Center put SPY against QQQ at 54% overlap by weight, with 84% of QQQ's holdings also in SPY but only 17% of SPY's in QQQ. A small fund inside a large one looks almost entirely duplicated from its own side and barely present from the other. Ask the question from the fund you are thinking of dropping.