This post updates a post I wrote over five years ago, Tax Tail Wags Investment Dog, about the tax effects of Exchange Traded Funds (ETFs). I decided an update was in order after seeing the massive flows into ETFs in the first quarter of 2026 and that the authors had updated the paper on which I based my 2021 post with four more years of data. The tax effects of ETFs are clearly happening faster and are larger than I expected.1 That is bad news for federal and state income tax revenues.
In a nutshell, the ETF structure provides a classic example of how financial engineering, the realization requirement, and step up in basis undercuts taxation of capital gain income – especially when Congress fails to constrain or limit efforts by the tax planning industry to exploit seams in the tax code. That is likely reducing federal tax revenues by over $20 billion/year and growing.
The favored taxation of ETFs is largely due to four factors:
- An unintended effect of a provision of the Tax Reform Act of 1969
- Favorable decisions by the SEC
- Exploitation of the literal language of the tax law
- Inattention by Congress
It is clear now that the effects, unless addressed by Congress, will lead to the loss of hundreds of billions of dollars in tax revenue. This has, as far as I can tell, been largely flying under the radar.2 It is also unintended and undercuts the fairness and efficiency of the tax system. But we’re stuck with it, absent a seismic change in Congressional attitudes and practices.
ETFs’ tax advantage
Here’s a short version of the how and why of ETF’s favored tax treatment. For a fuller account, see Colon, Unplugging Heartbeat Trades and Reforming the Taxation of ETFs.
Mutual funds, which ETFs are a subset of, are subject to form of pass-through taxation. They are pooled investment funds owned by their shareholders. When the fund sells appreciated securities and recognizes gain, that income is passed-through and taxed to the shareholders.3 Thus, even though the shareholder has done nothing he/she may receive distributions of capital gains (or dividends for short term gains) reported on a Form 1099, because the fund itself has sold securities.4 Interest and dividends earned by the funds are similarly subject to pass through taxation, losses are not (they offset gains at the fund level).
For traditional mutual funds, distributions to satisfy shareholder redemptions are almost always made in money.5 However, the Tax Reform Act of 1969 included a provision that allows funds to instead provide for redemptions “in kind” – i.e., to hand over some of the fund’s portfolio securities to the shareholder. Congress’s rationale for making this minor change is unknown; there isn’t any written legislative history for it. It was done when Congress started to limit the ability of corporations to distribute appreciated property tax free (the General Utilities doctrine).
Making in-kind redemptions is rarely done by traditional mutual funds, by all accounts.6 That changed with the advent of ETFs in 1993 (i.e., 24 years later); they routinely do it as part of their general mode of operation.
ETFs trade on public stock exchanges. And, unlike closed-end funds, the number of outstanding ETF shares can go up or down based on market demand (i.e., they’re open-end funds). To keep their net asset values or NAVs (i.e., the value of the securities in the fund’s portfolio) aligned with the minute-to-minute changes in value of the aggregate value of outstanding ETF shares (again, all the relevant securities are typically trading on stock exchanges) requires use of in-kind redemptions through Authorized Providers or AP (essentially market makers for the ETF shares). The AP and the ETF swap shares back and forth to keep the two sets of values aligned. The shares being swapped are ETF shares themselves and the portfolio holdings (stocks for an equity ETF) of the ETF.
This swapping creates the opportunity for the ETF to purge its portfolio of low-basis shares and their potential for the ETF itself realizing capital gains that must be distributed to shareholders – i.e., when the ETF has to dispose of portfolio shares because of changes in its investment plans or sales/redemption of the ETF shares. Of course, that requires some minimum level of swapping and the authority to pick low-basis shares to do it. The SEC provided regulatory guidance provided the necessary leeway – i.e., allowing use of custom baskets of shares (e.g., low-basis ones) rather than requiring pro rata lots, a proportionate distribution of all the ETF’s portfolio securities.
The swapping and that guidance allowed the fund industry to develop the practice of “heartbeat trades” – essentially extra swapping with the AP to purge the low-basis securities. It’s extra swapping because it’s not necessary either to keep prices aligned or to satisfy purchases or sales of ETF shares. They’re doing for the purposes of getting rid of the low-basis holdings to insulate their shareholders from distribution of capital gains.
In addition, Vanguard came up with the idea of adding an ETF share class to a traditional mutual fund. That allowed it to use heartbeat trades to purge low basis holdings in the traditional fund as well. Vanguard patented that technique and the SEC also authorized it. The patent has expired and the SEC has provided general guidance for other funds to use the technique, which they have started doing.
Net result: Expanded use of ETFs, thus, reduces both capital gain distributions from mutual funds and dividends (short term gains are distributed by mutual funds as dividends).7 Use of ETFs has sky rocketed. Tax revenues similarly declined.
Flows
Overall
An ETF.com post, Q1 ’26: The State of the (Bonkers) ETF Market (3/27/2026), reports massive flows into ETFs (my emphasis):
ETF assets are roughly $13.8 Trillion, now spread across 5,046 funds. * * * Vanguard pulls roughly $1.5B per day. VOO [Vanguard’s S&P 500 ETF] alone absorbed $39.3B YTD. * * *
And the flows are also bonkers! Year-to-date inflows ($446B) are running 64% ahead of 2025’s record pace: on track for $2T+, seven years ahead of Bloomberg Intelligence’s 2024 forecast for when we might hit that kind of number.
The post also reports that 231 new ETFs have been created in 2026 and have gathered over $37 billion in assets. By contrast, the Investment Company Institute, the industry trade association, reports traditional mutual funds have experienced outflows of more than $32 billion. Thus, in one quarter, almost half a trillion in assets flowed into ETFs while $32 billion flowed out of traditional mutual funds.
More actively managed ETFs
Actively managed mutual funds are inherently less tax efficient than index funds, because the active managers regularly buy and sell investments to maximize returns. That is what active management is all about. Indexing is a permanent buy and hold strategy with capital gain triggering selling only done if the index changes or if money is needed to pay for shareholder redemptions. Trading causes the fund to realize capital gains that are distributed to shareholders yielding tax liability.
ETFs traditionally were index funds, including those based on more exotic indexes constructed using various financial metrics (dividend history, volatility, etc.). But the according to the ETF.com post, the recent flows are often to actively managed ETFs:
A big part of this flood will be * * * [flows into] active ETFs. While we could do a lot of splitting hairs on just how “active” a lot of them are, there are indeed now more active than passive ETFs: 2,751 vs. 2,295. 84% of 2026 launches are active, with flows that mirror. Active is gaining assets at 3X its base: 12% of assets but 38% of flows.
One might naively assume that doesn’t matter. If actively managed ETFs are trading stocks and bonds, just like traditional mutual funds they will need to distribute any resulting capital gains to shareholders, typically generating tax liability. Wrong. As described above, ETFs’ ability to distribute low-basis securities to their Authorized Providers (AP) effectively can wash away many of those capital gains, especially with the ability to use “heartbeat” trades. For example, this State Street post reports in 2025 that 53% of active mutual funds distributed capital gains, while only 9% of active ETFs did. The post makes the point that tax savings are the big driver of the ETF onslaught.
Conversions
In addition to new launches, fund complexes are converting traditional mutual funds to ETFs. For example, the ETF.com post notes Dimension converted multiple of its funds to ETFs and plans to do more. I assume that accounts for some portion of the ETF in-flows and traditional funds’ outflows.
As the trend to ETFs continues, it will be harder to resist converting. ETFs not only are more tax efficient, but they also have lower fees. Those two factors should make it a no-brainer for taxable accounts to select an ETF when both flavors are available for an otherwise equivalent fund. Fund complexes still offering only traditional funds will be at a competitive disadvantage.8
Share class option
As noted above, Vanguard developed a patented structure that bolts an ETF onto a traditional fund as a separate share class, allowing the ETF’s use of heartbeat trades to cleanse the traditional mutual fund of its low-basis securities, reducing capital gain distributions for its shareholders.9
The ETF.com post describes the industry response to patent’s expiration:
The share class story is well trod at this point: the Vanguard patent for ETF share classes of traditional mutual funds expired in 2023, and by last December the SEC had granted exemptive relief to over 30 firms. Two weeks ago, on March 17th, the SEC completed the transition to this new era by issuing the final Exchange Act relief for multi-class ETFs.
(That sound you heard was a starting gun.)
About 100 applications are in, about 70 orders issued. 2 firms launched.
Longer term trend
To get a fuller picture, I went on FRED and captured data on the relative AUMs of all mutual funds and ETFs, including those holding bonds and other fixed income securities, as well as international stocks and bonds.
The following graph shows the data with the top line representing total mutual fund assets (including ETFs) and the bottom line, ETF assets. The lines are converging and likely will get much closer together. To express it in percentages, at the end of 2024 ETF assets were 49% of the total and now are closer to 58%. That’s an astounding increase in a little over a year and a quarter.10

Updated Article
I noticed via this Harvard Law School Forum post that the Moussawi, Shen, and Velthuis SSRN paper that I based my 2021 post on was updated in April of 2025. (The Harvard post is a very short summary that can be read in a minute or two.) The paper’s analysis now reflects an additional four years of data (through 2023) and more analysis (e.g., of the effect of the Vanguard share class strategy and tax-free conversions of traditional mutual funds to ETFs). Their data, of course, is still somewhat stale; it doesn’t reflect the tidal wave of ETF growth in the last year plus.
The updated article, which will be published in Review of Financial Studies, essentially presents the same story as before: the favorable tax status (i.e., deferral of most capital gains) is what is driving ETF growth. The ability to do conversions and the now general availability of the Vanguard share class strategy will only increase the amount of assets in ETFs, compared with traditional funds. The updated article has a wealth of additional information – a lot has happened in the intervening four years.11
This graph (Figure V, Panel B, p. 41) from the article illustrates the dramatic tax advantage of ETFs. It expresses realized capital gains as a percentage yield for the three types of funds:

The percentage rates are low, all under 8%. But with total AUM for all mutual funds now over $28 trillion, small percentages translate to large amounts.
The paper’s additional four years of data provides more information and certainty to its estimate of the potential effects on federal tax revenues from the migration of financial assets to ETFs. Using data through 2019, the 2021 version estimated deferral of capital gains between $400 billion and $679 billion (10-year estimate). The updated version raises that estimate to $915 billion to $1.7 trillion. (Note: the article’s data is limited to U.S. equity ETFs. Thus, it excludes ETFs that invest in foreign equity or fixed income securities. The latter generate only modest capital gains, of course.)
This is how the article (p. 32) describes the potential revenue effects:
Given that U.S. equity ETFs managed around $4.6 trillion in assets by the end of our sample period (Table A.I), it is reasonable to assume that these ETFs would contribute to the deferral of the tax on at least $915 billion and up to $1.7 trillion in short- and long-term capital gains distributions over the next decade. These projections will be much higher if we incorporate additional ETFs traded in the U.S. (other non-U.S. equity and fixed income ETFs with the in-kind redemption feature, estimated to be around $2.8 trillion in size in 2023 according to Investment Company Institute (2024)), as well as future investors’ flows into ETFs. The tax-deferral feature of ETFs also allows tax-free compounding of short- and long-term capital gains, creating larger accumulated future capital gains. Furthermore, investors can forgo paying taxes on the accumulated capital gains if they bestow their ETF shares due to the step-up in basis rule, disproportionally benefiting wealthier investors who have been migrating to ETFs in recent years.
Those numbers reflect the amount of gain deferred. To translate that to reduced tax revenue, one must make assumptions about the percentage of the deferred gains that are ultimately avoided altogether through stepped up basis (i.e., if the ETF shareholder sells, she/he will then recognize the gain based on their basis in the ETF shares) and what tax rate would have applied. Assuming 75% of the gains ultimately avoid taxation altogether and that the applicable federal rate is 15% (both of those are conservative, I think) suggests a potential 10-year revenue loss of about $150 billion.
That amount is surely very low because the paper’s numbers do not reflect:
- The very large flows into ETFs since 2023
- ETFs that invest in foreign equities and fixed income securities
- The subsequent growth of active ETFs which have proportionately more capital gains when the traditional structure is used12
- Growing use of private 351 ETFs by high-net-worth individuals to diversify holdings of concentrated direct stock holdings, such as founder stock or similar
- Use of ETFs to avoid the wash sale rule (see Appendix).
I would not be surprised if the use of ETFs will lead to $300 billion in reduced federal revenue over the next ten years.13
The bottom line is that Congress’s failure since the 1990s to regularly update the tax code to limit these sorts of arrangements has had a major impact on revenues and the budget deficit. And this is just one example. It also helps to explain why recipients of capital income pay lower effective rates than wage earners, modestly boosting income inequality. With regard to SALT considerations, it is a cautionary tale for states who are attracted (for reasons of enhancing equity and revenue yield) by the proposals to increase their reliance on taxing income from capital. That income tends to melt away, in addition to being more volatile and harder to collect.
Appendix
The Appendix provides two anecdotes of how ETFs are used to avoid paying taxes, almost certainly inconsistent with the intent of the Code when the relevant provisions were enacted.
Tax-free T-bills?
One ETF, BOXX, provides an example of how the combination of financial engineering, the ETF structure, and a market for tax avoidance (w/ IMO questionable cost-benefit payoff) can lead to the development of exotic investment products.
This 2022 Bloomberg article, T-Bills Without Tax Bills? This Fund Says It Cracked the Code, describes how an enterprising former Marine used the ETF structure to obtain preferential capital gain taxation on what is essentially an alternative to money market investments. In other words, deferral until realization and then lower federal tax rates for long-term gains apply. Tax liability, of course, can be washed away by the step up in basis rules if the fund holding pass on death. This Morningstar article explains how the investment element works. The underlying investments are option contracts on stocks – nothing close to T-bills.
There are doubts as to whether the tax angle works technically. See Steve Rosenthal at TPC and Professor Daniel Hemel for more details. But the fund has been around for four years and, according to Morningstar, now has $11 billion in assets. That is a niche fund by most standards. As of the first quarter end, Fidelity’s government securities money market fund had over $400 billion in assets, by comparison. But it still must have a very large number of shareholders.
I have seen no reports in the financial or tax press that the IRS has attacked the tax strategy. If it does and is successful, the compliance and administrative issues will be an unholy mess, given the large number of shareholders and the multiple tax years involved. (For all I know, the promoters may have gotten a private letter ruling – I no longer have access to a databased of PLRs.)
A couple of observations, to get the favored federal tax treatment (i.e., long-term capital gains) one needs to hold the investment for at least a year. That is not ideal for one’s cash or most liquid holdings. It is more likely to work for someone who wants a longer-term investment with a cash-like return. There are plenty of good investment arguments against that. It used to be truism that holding cash was not really an investment. However, there is some case for holding cash as a better diversifier than longer term fixed rate investments (e.g., see this column by John Rekenthaler). Second, Morningstar gives BOXX a negative rating. Its expenses are high – the fund’s operators siphon off a fair chunk of the tax savings and the fund is riskier than a money fund and certainly than holding T-bills.
SALT implications. From a state tax perspective, if the alternative is holding T-bills as suggested by the promoter, investors forgo their state tax exemption in doing so. Federal law prohibits states from taxing interest on Treasury securities. So, if investors abandon T-bills for BOXX, it’s a small plus for state income taxes without capital gain preferences (e.g., California and Minnesota). Those states will realize tax when the investor sells and realizes a taxable capital gain versus T-bill interest that is free of state tax. In addition, for million-income folks in Minnesota, the NIIT surtax applies if the gains are realized by selling the ETF. Of course, if the interests are never sold (i.e., they pass at death), there will be no state tax.
Avoiding wash sales
The wash sale rule prevents buy and selling essentially the same security within a short window of time to realize a capital loss without actually changing your position economically or financially. This would be classic gaming of the realization requirement and has been prohibited for over a century.
The proliferation of ETFs (e.g., multiple ETFs tracking the same index) creates the opportunity to avoid the wash sale limit. Sell a Vanguard ETF and buy an identical Fidelity ETF nearly simultaneously does not change one’s investments as a financial or economic matter. A recent academic study, ETFs and the Wash Sale Loophole (June 13, 2025), documents that institutional investors are routinely doing that. Here’s a quote from the abstract:
This study examines whether institutional investors use ETFs to circumvent wash sale rules. Consistent with tax-motivated demand for ETFs, incumbent ETFs both create more shares and experience more trading volume upon the introduction of nearly identical ETFs, particularly when recent returns are negative. We show tax-sensitive institutions’ investment in highly correlated ETFs has proliferated in recent years, exceeding a quarter of their AUM. Furthermore, tax-sensitive institutions holding more ETFs are significantly more likely to engage in swapping nearly identical ETFs. This swapping behavior has become widespread, with tax-sensitive institutional investors swapping $417 billion of nearly identical ETFs since 2001. We estimate that tax-sensitive institutions realized more than $84 billion dollars in losses in highly correlated ETFs associated with the swapping activity since 2001.
Those revenue losses, in the larger scheme of things, are modest. But even saving a few billion dollars matters. In 1997, for example, Congress largely foreclosed a wash sale avoidance strategy called short against the box that was widely used. (Disclosure: I used the short against the box technique a few times back in the 1990s. I have also used the ETF strategy recently and likely will again unless the law changes.) Congress largely has abandoned doing that sort of thing.
Notes
- This is what you would expect when Congress has largely abdicated its duty to protect the tax base from exploitations of gaps in law. In the 1980s and early 1990s, it did this routinely, enacting technical corrections bills and revenue raisers that closed new fissures. Anyone paying attention to federal tax policy recognizes that has not been happening in the last 25+ years. Ray Madoff makes that point in her book, The Second Estate. (Madoff’s focus is the failure to address estate and gift tax avoidance; the revenue effects for the income and corporate taxes are almost certainly larger.) It’s a sure recipe for reducing the tax on capital income. That is so because financial engineering can easily reconfigure income from investments and business operations to take legal forms that minimize its taxation. Aggressive regulations and judicial interpretations can staunch only so much of that. The real solution is for Congress to regularly tweak the Code’s language to foreclose the worst of those efforts. ETFs’ use of heartbeat trades is a classic example. See this law review article for detailed explanation of how a seemingly innocuous provision enacted in 1969 became a multi-billion-dollar tax break for ETF investors and providers. The article contends that Congress needs to fix the provision. I agree but now that the tax break has become embedded in expectations and there is more than a cottage industry benefitting from it, Congress will almost surely do nothing. It took Congress years to even partially close down syndicated conservation easements, most of which could only accurately be considered a scam. ↩︎
- In 2021, Senator Wyden proposed changes (see section 17) that would repeal tax-free in-kind redemptions for mutual funds. It went nowhere. I’m not sure it was even formally introduced. He also proposed in 2025 limiting the ability to create designer ETFs that allow individuals with concentrated portfolios (classic example would be founder stock in a successful tech startup) to diversify their holdings using designer ETFs. ↩︎
- Unlike S corps and partnerships, the pass-through treatment is crimped or partial. Losses are not passed through but retained in the fund and offset future gains. Short gains are passed through as dividends, so they can’t be offset by capital losses. ↩︎
- The shareholder will receive a distribution of money or fund shares (if the shareholder has elected to reinvest dividends or capital gain distributions), of course. If reinvested her basis in the fund will increase accordingly. ↩︎
- A typical mutual fund shareholder who requests a redemption would be shocked to receive portfolio securities instead of money. ↩︎
- The change was likely stimulated by the 1969 Act’s start of limitations on the rule in General Utilities – i.e., the ability of corporations to distribute appreciated property to shareholders without recognizing gain. See the text of the Colon article at notes 84 to 93 for possibilities as to Congress’s rationale. It’s clear no one thought at the time there would be significant revenue consequences to the 1969 change or when it was confirmed in the Tax Reform Act of 1986, which repealed the General Utilities doctrine. ↩︎
- Matt Levine, who writes a great free Bloomberg newsletter on financial markets, characterizes ETFs as mutual funds that don’t pay taxes, as well as an easy way to package trades. This combination explains their explosive growth. I highly recommend subscribing to his newsletter, if only for its entertainment value. ↩︎
- Tax savings are irrelevant to retirement funds and other tax-exempt entities, but ETFs’ generally lower fees are important. Retirement funds, like 401(k)s, may violate their sponsor’s fiduciary duties to participants if they don’t select/offer lower fee funds. A plethora of lawsuits have challenged employers whose 401(k) plans offer higher-fee funds. ↩︎
- I have personally benefited from the tax savings this structure provides. We have held three traditional Vanguard mutual funds in taxable accounts for a long time. They are based on narrower indexes and typically generated a modest amount of capital gain distributions until the ETF share classes were added. After that, the capital gain distributions totally stopped – now for well over a decade. That is so, even though the funds track indexes with stocks regularly being added and dropped from the indexes, while the value of the stocks they hold have appreciated substantially. The revised version of the Moussawi, Shen, and Velthuis article documents that my personal observation is the case for the Vanguard funds with ETF share classes. They have totally stopped distributing capital gains. See Appendix C. ↩︎
- The two lines are unlikely to converge – i.e., that ETFs will not totally replace traditional open-end mutual funds. There are investment reasons to prefer traditional mutual funds under some circumstances, such as liquidity issues. Moreover, the tax advantage doesn’t matter for retirement accounts or other tax-exempt investors, although ETFs’ typically lower fees do. On that front, fund complexes will not like their low fees (= lower profits and manager compensation) and so will drag their feet in moving all their AUM to the ETF structure. In addition, SEC rules require much more frequent disclosure of the portfolio holdings of ETFs compared to traditional mutual funds. This can be a disadvantage for actively managed funds that do not want to disclose their investment strategies, particularly as they are adding to or shedding holdings. ↩︎
- For example, with regard to the share class strategy, the article (p. A-20) cites a Bloomberg estimate, which I had not seen, that its use reduced Vanguard shareholders’ realized capital gains by $130 billion through 2018 (well over $20 billion in federal tax). Absent a favorable SEC decision, the share class strategy likely could not have been implemented. ↩︎
- The paper assumes that ETFs are index type investments. It treats active funds and ETFs as mutually exclusive categories. That appears to be less likely to be the case now, since 2025 and 2026 data show many more active ETFs, even though they may mainly be algorithm-based strategies and not classic manager-picked active funds. ↩︎
- In 2021, JCT staff preliminarily estimated that Wyden’s proposal (completely repealing tax-free in-kind redemptions) would have raised $206 billion. I’m sure they estimated a healthy rate of growth in the use of ETFs, but I doubt it was close to what is actually happening. The 2025-26 surge has surprised most observers, including industry sources. ↩︎






