Why ETFs Tracking the Same Index Can Deliver Different Returns

Two ETFs can carry almost identical names, follow the same benchmark, and still leave investors with different results. The reason is simple: an index is only a set of rules. An ETF is a real investment product that must turn those rules into an actual portfolio, manage cash flows, execute trades, process dividends, and provide liquidity to buyers and sellers.

That gap between theory and implementation matters. Choosing an ETF based only on its benchmark or recent return can hide costs and risks that become visible later. A better comparison looks at how efficiently the fund delivers the exposure it promises—and what investors actually pay to enter, hold, and exit the position.

The Expense Ratio Is Only One Part of the Cost

The expense ratio is the most visible difference between competing ETFs. If two funds follow the same index but one charges a higher annual fee, the more expensive fund begins with a structural disadvantage. Over a long holding period, even a modest difference in annual costs can compound into a meaningful performance gap.

But the cheapest ETF is not automatically the best tracker. Securities-lending income may offset part of a fund’s expenses, while transaction costs, taxes, cash balances, and the timing of index changes can create additional drag. Fund managers also differ in how efficiently they process subscriptions, redemptions, dividends, and portfolio rebalancing.

This is why investors should distinguish between tracking difference and tracking error. Tracking difference measures how much an ETF outperformed or underperformed its benchmark over a specific period. Tracking error measures how consistently the fund stayed close to that benchmark along the way.

A fund can have a small, predictable shortfall caused mainly by its annual expenses. Another may finish the year near the benchmark but move above and below it much more erratically. MEXC’s guide to premiums, discounts, and tracking error in stock-linked products explains how fees, distributions, taxes, pricing methods, and operational frictions can affect the relationship between a product and its reference asset.

For long-term investors, the useful question is not simply, “Which ETF has the lowest fee?” It is, “Which fund has delivered the most efficient and consistent exposure after all costs?”

The Same Benchmark Can Be Replicated in Different Ways

An ETF does not always hold every security in its benchmark at exactly the published index weight. A fund tracking a relatively simple, liquid index may use full replication, meaning it buys all or nearly all the underlying securities. An ETF following a much broader or less liquid market may use representative sampling, holding a smaller basket designed to behave like the full index.

Sampling can make a fund easier and less expensive to operate, particularly when an index includes hundreds or thousands of securities. However, it also introduces another source of tracking risk. If the selected holdings do not respond exactly like the securities left out, the ETF may temporarily diverge from the benchmark.

Even fully replicated funds face practical constraints. Index providers periodically add and remove constituents or change their weights. ETF managers must then trade the affected securities, sometimes when many other index-tracking funds are trying to do the same thing. The timing and cost of those trades can influence performance.

Cash management also matters. New investor money may not be invested immediately, while dividend payments can remain in cash until they are distributed or reinvested. When markets are rising quickly, this cash drag may cause a fund to trail its index. In falling markets, the same cash position can have the opposite effect.

MEXC’s view is that ETF quality should be judged by the reliability of the implementation process, not by the familiarity of the fund name or one year of headline performance. A well-run ETF should produce deviations that are limited, understandable, and reasonably consistent across different market conditions.

Trading Costs Can Outweigh a Low Annual Fee

The expense ratio affects investors gradually, but trading costs are felt as soon as an order is executed. ETFs trade on exchanges, where buyers quote one price and sellers quote another. The difference between the best bid and the best ask is the bid-ask spread.

For a large, actively traded ETF, that spread may be relatively narrow under normal market conditions. A smaller or more specialized fund may have a wider spread, meaning an investor gives up more value when entering or exiting the position. If the order is large relative to the available market depth, it may also execute across several price levels and create additional slippage.

This creates an important distinction between long-term and short-term costs. A long-term investor may care most about annual expenses and persistent tracking differences. A frequent trader may be affected much more by spreads, slippage, and intraday price deviations. A small advantage in the expense ratio can easily be overwhelmed by poor execution if the ETF is traded often.

Trading volume alone does not tell the full liquidity story. Investors should also consider the depth of the order book, the liquidity of the underlying securities, and the ability of market makers to hedge the ETF. The MEXC analysis of liquidity and bid-ask spread risk explains why spreads depend on market depth, volatility, the underlying basket, and the mechanics of the specific product.

Timing can matter as well. If an ETF trades while some of its underlying markets are closed, the latest net asset value may rely partly on stale prices. The ETF’s market price may then reflect new information before the underlying securities reopen. During periods of stress, spreads can widen and the ETF may trade at a larger premium or discount to its reported net asset value.

A premium does not necessarily mean the ETF is permanently overpriced, and a discount is not automatically a bargain. Investors need to ask whether the reference value is current and whether the price gap can be traded efficiently after spreads and other costs.

Currency, Dividends, and Fund Structure Change the Return Investors Receive

Global ETFs add another layer to the comparison: currency exposure. Consider two funds that both track the same US equity index but are offered to investors using a different home currency. One fund may hedge currency risk, while the other leaves the exposure unhedged. Their equity holdings can perform identically, yet their investor returns may differ because of exchange-rate movements and hedging costs.

The trading currency shown beside an ETF is not always the same as its economic currency exposure. An ETF may trade in euros, pounds, or another currency while still holding assets whose value is mainly driven by the US dollar. Investors therefore need to look beyond the currency in which the ETF is quoted and examine whether the underlying exposure is hedged.

Dividend policy can also make similar funds appear different. A distributing ETF pays eligible income to investors, while an accumulating ETF reinvests it within the fund. Comparing the price chart of a distributing ETF with a total-return index can be misleading because the chart may not include cash already paid out. Fair comparisons should use the same return basis and period.

Fund domicile, tax treatment, replication method, and legal structure can introduce further differences. Two ETFs following the same index may face different withholding taxes or operate under different regulatory frameworks. Investors may also encounter products that provide similar economic exposure without offering the same ownership rights, redemption process, or risk protections.

These distinctions become especially important when comparing ETFs with individual stocks, Tokenized Stocks, or derivative products. MEXC’s guide on choosing between RealStocks, Tokenized Stocks, Stock Futures, and ETFs highlights how holding period, liquidity, costs, legal claims, and product structure can alter the investor experience even when the underlying market exposure looks similar.

A Better ETF Comparison Starts With the Investor’s Objective

Past performance is useful, but it is not enough to identify the better ETF. A fund may temporarily outperform because of currency movements, cash holdings, tax treatment, or a short-lived deviation from its benchmark. None of these necessarily indicates superior long-term management.

A more useful comparison begins by confirming that both funds track the same version of the index. A price-return index and a total-return index are not equivalent because only the latter assumes that dividends are reinvested. The comparison period and currency basis must also match.

Investors can then examine the expense ratio, historical tracking difference, tracking error, bid-ask spread, fund size, replication method, distribution policy, currency-hedging policy, and underlying holdings. The relative importance of each factor depends on how the ETF will be used.

For a long-term core holding, a consistent tracking record and low recurring costs may matter most. For tactical exposure, liquidity and execution quality may deserve greater weight. For international investing, currency policy and tax treatment can be as important as the benchmark itself.

The goal is not to find an ETF with the most attractive single statistic. It is to find a product that delivers the intended market exposure through a transparent structure, at a reasonable total cost, with sufficient liquidity for the investor’s expected position size and holding period.

FAQ

Is the ETF With the Lowest Expense Ratio Always the Best Choice?

No. A lower expense ratio reduces one source of cost, but it does not account for tracking quality, bid-ask spreads, liquidity, taxes, currency exposure, or fund structure. Total ownership and trading costs provide a more complete comparison.

Why Does an ETF Sometimes Trade Above or Below Its Net Asset Value?

An ETF’s market price is set by buyers and sellers, while its net asset value is calculated from the underlying portfolio. Differences can emerge when markets are volatile, underlying securities are difficult to trade, or some of the relevant markets are closed. Creation and redemption mechanisms can help keep the two values aligned, but they do not guarantee an exact match at every moment.

Does a Larger ETF Automatically Carry Less Risk?

Not necessarily. A larger asset base may support liquidity and reduce the possibility of the fund being closed, but it does not remove market, concentration, currency, or tracking risk. The ETF’s holdings and index methodology still determine the underlying investment exposure.

Should Long-Term Investors Care About Bid-Ask Spreads?

Yes, although spreads usually matter more to frequent traders. Every investor eventually needs to enter and exit the position, and a wide spread can reduce the return realized from those transactions. The impact should be assessed alongside the expected holding period and position size.