When you buy an exchange-traded fund, the expense ratio is the first number you check. A low fee, say 0.03 percent, feels like a bargain. But that number is not the whole story. Buried in the fine print is a mechanism that lets the fund manager earn trading profits by trading against your own holdings. You pay the expense ratio, and you also pay indirectly when the manager profits from your portfolio. This double charge can quietly drain returns for years.

The Fee That Breeds a Conflict

The expense ratio is supposed to cover the cost of running the fund — management fees, custody, administration, and trading costs. But trading costs are not a simple line item. When the fund buys and sells securities, it generates brokerage commissions and bid-ask spreads. Those costs are borne by the fund, meaning by you. However, the fund manager can also earn revenue from the same trading activity.

How? Some fund managers operate their own trading desks. When the fund places a trade, the manager can execute it internally, acting as the counterparty. The manager buys or sells the security to the fund at a price that includes a spread — a profit for the manager. This is effectively a markup on every trade. The fund's returns are reduced by that markup, and the manager pockets the difference.

Securities and Exchange Commission rules permit this arrangement, as long as the manager discloses it in the prospectus and executes trades at fair market value. But fair market value is a range, not a single price. The manager can consistently take the favorable side of that range, extracting a small profit on each trade. Over thousands of trades, the total can be substantial.

A study by a quantitative finance researcher, published in 2023, estimated that this trading-profit extraction adds roughly 0.2 to 0.5 percent annually to the true cost of owning an ETF. That is on top of the stated expense ratio. For a fund with a 0.03 percent expense ratio, the real cost could be ten times higher.

How the Manager Profits Twice

The manager collects the expense ratio as stated. That is the first profit. The second profit comes from the trading desk. When the fund rebalances, or when investors create or redeem shares, the manager must buy or sell underlying securities. If the manager's broker-dealer affiliate handles those trades, it can charge a spread or commission. The revenue flows to the manager, not back to the fund.

This is not illegal, but it is a conflict of interest. The manager has an incentive to trade more frequently than necessary because more trades generate more profit. The fund's stated investment objective may call for low turnover, but the manager's trading desk benefits from churn. The expense ratio does not capture this incentive.

Disclosure rules do not require a separate line item for trading profit. The fund's financial statements show net investment income, net realized gains, and expenses. The trading profit is embedded in the cost basis of securities bought and the proceeds of securities sold. It is invisible to the typical investor. Computational finance models used by the fund to value its holdings do not flag this leakage because the models assume arm's-length pricing.

The gap in disclosure is like a haircut that never appears on your statement. In finance, a haircut is the discount applied to collateral. Here, the haircut is the hidden spread the manager takes. You see the expense ratio, but not the cost of the manager trading against you.

Evidence from Prospectus Footnotes

Look at the Statement of Additional Information for any large ETF. Vanguard and BlackRock, for example, disclose that they earn brokerage income from trading activity. In Vanguard's SAI for its Total Stock Market ETF, a footnote states that the fund may pay commissions to broker-dealers that are affiliates of the manager. That is a polite way of saying the manager can be the counterparty.

BlackRock's filings show revenue from securities lending, another hidden profit center. The fund lends out its shares to short sellers and earns a fee. The manager keeps 60 to 80 percent of that lending revenue, depending on the arrangement. The expense ratio already covers custody and administrative costs. The lending revenue is pure profit for the manager, and it comes at the expense of the fund's shareholders, who bear the risk of the borrower defaulting.

Securities lending is disclosed, but the magnitude is hard to parse. A 2024 analysis by the Investor Protection Trust found that the average ETF keeps only 20 to 40 percent of lending revenue. The manager takes the rest. Over a decade, that can amount to several basis points of annual return. Combined with trading profit, the total hidden cost may reach 0.3 percent or more.

The double-dip is hidden in plain text. The prospectus says the manager may engage in principal transactions. The footnotes disclose securities lending splits. But few investors read those documents. The industry norm is to focus on the expense ratio, which is prominently displayed on every fund page.

The Real Cost to Your Returns

An expense ratio of 0.03 percent is not the total cost. If trading profit extraction adds 0.2 percent and securities lending retention adds another 0.1 percent, the true cost is 0.33 percent. That is not a disaster, but it compounds. On a $100,000 portfolio over 30 years, assuming a 6 percent annual return, a 0.33 percent annual drag reduces the ending balance by roughly $18,000 compared to a 0.03 percent drag. That is money that could have funded retirement or a child's education.

Index funds are not immune. In fact, ETFs are more vulnerable because they trade on exchanges and have a creation-redemption mechanism that generates frequent trades. Actively managed funds may also engage in principal trading, but the effect is harder to isolate because active management already has higher fees.

The Federal Reserve has taken notice. In June 2026, the Fed issued enforcement actions against former employees of two banks for misconduct related to securities lending. While those actions targeted individual wrongdoing, they signal that regulators are scrutinizing the revenue streams that flow from fund assets. The Fed's 2025 review of asset management activities found no consensus on whether to ban principal trading by fund managers, but the issue is on the table.

For now, the cost is real and mostly invisible. If you own an ETF, you are likely paying more than the expense ratio suggests. The question is whether you can avoid it.

Why Regulators Haven't Stopped It

There is no explicit ban on proprietary trading by fund managers. The Volcker Rule, part of the Dodd-Frank Act, restricts banks from proprietary trading, but it carves out asset management activities. A fund manager that is part of a bank holding company can still trade against its own funds as long as the trading is in connection with the fund's operations.

Haircut rules, which require banks to hold capital against risky assets, do not apply to fund assets. The fund's securities are held by a custodian, but the manager's trading desk is separate. The regulatory framework focuses on the fund's disclosures, not on the manager's internal profit centers.

Disclosure rules require the fund to list its expense ratio and any fees paid to affiliates. But the SEC does not mandate a line item for trading profit or securities lending revenue. The industry has lobbied against such requirements, arguing that they would be burdensome and would reveal proprietary trading strategies. The SEC's 2025 review of the fund disclosure framework found no consensus among stakeholders on whether to require more granular cost breakdowns.

Reform is possible but slow. The SEC could require funds to report the total cost of ownership, including trading spreads and securities lending retention. But until that happens, the expense ratio remains the only standardized number, and it understates the true cost.

What You Can Actually Do About It

First, read the Statement of Additional Information, not just the prospectus. Look for language about principal transactions and securities lending. If the fund discloses that it may trade with affiliates, that is a red flag. Some funds, like those from Dimensional Fund Advisors, explicitly state that they do not engage in principal transactions with affiliates.

Second, check the securities lending revenue split. Some funds, such as those offered by Vanguard, rebate a portion of lending income to the fund. Vanguard's structure, where the fund owns the management company, means that profits from securities lending flow back to the fund, reducing costs. In contrast, BlackRock's iShares ETFs typically keep a smaller share of lending revenue for the fund.

Third, consider direct indexing for large portfolios. Direct indexing lets you own the underlying stocks directly, avoiding the fund structure entirely. You pay a management fee, but there is no ETF expense ratio and no securities lending. The trade-off is complexity and higher minimums. For portfolios over $500,000, the savings may justify the effort.

Finally, accept that some drag is unavoidable. No investment is free. The key is to be aware of the hidden costs and to choose funds that minimize them. Compare not just expense ratios but also securities lending policies and trading practices. A fund with a slightly higher expense ratio but no principal trading may be cheaper overall.

Additional Examples of Hidden Costs in Practice

To illustrate the real-world impact, consider a mid-cap ETF tracking the S&P MidCap 400 index. The stated expense ratio is around 0.05 percent, but the fund's SAI reveals that the manager may engage in principal transactions with an affiliated broker-dealer. Assume the fund's annual turnover is 15 percent — typical for an index fund due to rebalancing and investor flows. If the manager captures an average spread of 0.1 percent on each trade, the annual cost from trading profit alone is 0.015 percent (15% turnover × 0.1% spread). That seems small, but combined with securities lending retention of 0.1 percent, the total hidden cost reaches 0.115 percent, more than doubling the stated expense ratio.

Another example: an international equity ETF with a 0.07 percent expense ratio. International funds often have higher turnover due to currency hedging and rebalancing across multiple markets. Turnover may reach 25 percent. If the manager's trading desk captures a spread of 0.2 percent on foreign trades (where bid-ask spreads are wider), the trading profit cost is 0.05 percent. Add securities lending retention of 0.15 percent, and the hidden cost totals 0.2 percent, nearly three times the stated ratio.

These estimates are conservative. Some funds, particularly those focused on small-cap or emerging markets, may have turnover exceeding 30 percent and spreads of 0.5 percent or more, leading to hidden costs of 0.3 percent or higher. The expense ratio alone is clearly insufficient to gauge total cost.

Counter-Arguments: Defenses of the Current System

Not everyone agrees that these practices are harmful. Fund managers argue that principal trading provides liquidity and efficiency. When the fund needs to execute a large trade, the manager's trading desk can step in as a counterparty, avoiding market impact and ensuring faster execution. This benefits shareholders by reducing the cost of trading, at least in theory. The manager's profit is compensation for taking on that risk.

Similarly, securities lending is defended as a way to generate additional revenue for the fund. Even though the manager keeps a large share, the fund still receives some income that reduces its net expenses. Without securities lending, the fund would have higher costs, and the expense ratio might be higher. The question is whether the split is fair.

Some industry participants argue that the current disclosure regime is adequate. They point to the requirement that principal transactions be at fair market value, and that securities lending revenue is disclosed in the financial statements. Investors who want to dig deeper can find the information. The problem, they say, is not lack of disclosure but lack of investor engagement.

However, these defenses overlook the conflict of interest. The manager controls both the fund's trading decisions and the trading desk's profit. There is no arm's-length negotiation. The manager can set the spread to maximize its own profit, within the range of fair market value. And securities lending arrangements are negotiated by the manager on behalf of the fund, but the manager's own compensation is tied to the revenue split. The incentives are misaligned.

Moreover, the argument that investors can find the information is weak. The SAI is long and dense. Most investors rely on the expense ratio as a summary measure. The industry's own marketing emphasizes low expense ratios. If the true cost were prominently displayed, investors would make different choices. The current system benefits managers at the expense of shareholders.

Trade-Offs: Direct Indexing vs. ETFs

Direct indexing offers a way to avoid the hidden costs of ETFs, but it comes with its own trade-offs. The management fee for direct indexing is typically around 0.1 to 0.2 percent, comparable to or slightly higher than the total cost of an ETF after hidden costs. However, direct indexing provides tax-loss harvesting opportunities that can add 0.5 to 1.0 percent in after-tax returns annually, especially for high-income investors. For taxable accounts, this can outweigh the fee difference.

But direct indexing requires a larger minimum investment, often $100,000 or more. It also involves more complexity: you need to manage a portfolio of individual stocks, monitor for corporate actions, and rebalance. For smaller portfolios, ETFs remain the more practical choice. The key is to select ETFs that minimize hidden costs.

Another alternative is to use mutual funds instead of ETFs. Mutual funds do not have the creation-redemption mechanism that generates frequent trades, so they may have lower trading costs. However, mutual funds can also engage in principal trading and securities lending, and they often have higher expense ratios. The comparison depends on the specific fund.

Ultimately, the best approach is to be informed. Read the fine print. Ask your financial advisor about the fund's trading practices. And remember that the expense ratio is just the starting point.

This article is for informational purposes only and does not constitute personalized investment advice. Consult a qualified financial professional for recommendations tailored to your situation.