Most European ETF investors are quietly sabotaging their own returns—not by taking too much risk, but by taking on too many funds. Overdiversification is the silent killer in modern ETF portfolios, and it’s eating into your gains in ways the industry would rather you never notice.
Let’s be blunt: The risks of overdiversification in ETF portfolios are real, pervasive, and rarely discussed with the urgency they deserve. While the gospel of diversification gets preached at every turn, European investors are being lulled into a false sense of security and mediocrity. In this deep dive, I’ll show you why chasing “perfect” diversification is a trap, how it’s costing you real euros, and what smarter investors are doing instead.
How Overdiversification Destroys Returns: The Numbers Don’t Lie
First, let’s define the crime. Overdiversification happens when your portfolio holds too many ETFs, many of which overlap in holdings or simply add dead weight. The result? Diluted returns, higher fees, and the illusion of safety.
According to Morningstar, the median European ETF investor now holds 8-12 separate funds, up from just 4 in 2015. Yet the marginal benefit to risk reduction drops off rapidly after the first 4-5 broad exposures.
Consider a typical scenario: a Dutch investor owns iShares Core MSCI World UCITS ETF (EUNL), Xtrackers MSCI USA UCITS ETF, and SPDR S&P 500 UCITS ETF. The dirty secret? Over 80% of the US and World ETF holdings overlap—think Apple, Microsoft, and Alphabet. This is not diversification, it’s redundancy dressed up with extra fees.
It gets worse. Add an emerging markets ETF and a Euro Stoxx 50 ETF, and you’re still barely moving the needle. MSCI World (EUNL) already covers over 1,500 global large and mid-cap stocks, including all the main European names. Each extra ETF chips away at your returns via incremental fees—maybe just 0.1% here and there, but compounded over 10 years and €100,000, that’s more than €1,000 down the drain for nothing.
Don’t even get me started on bond ETFs. As explored in our Eurozone government bond ETF guide, owning three different euro bond trackers gives you little extra protection compared to just picking the cheapest, broadest one. Diversification stops being useful and starts being expensive padding.
The Bottom Line
Overdiversification is where cautious European investors go to quietly lose money—and never notice until it’s too late.
Closet Indexing: The Silent Epidemic
There’s a name for this disease: closet indexing. Instead of building a sharp, purposeful portfolio, investors end up with a Frankenstein’s monster—bit of this, bit of that, until it becomes indistinguishable from the cheapest global index tracker.
In 2023, a study by Scope Ratings found that 61% of multi-ETF portfolios in Germany were functionally equivalent to a basic MSCI ACWI tracker—except for 2-3x the ongoing charges.
Why? Because most ETFs in Europe fish from the same narrow pond. Take the iShares Core MSCI World UCITS ETF (EUNL, TER 0.20%) and the Vanguard FTSE Developed World UCITS ETF (TER 0.12%). Both charge different fees, but over 90% of their top holdings are identical. Layering them together doesn’t add diversification; it adds pointless complexity.
If your portfolio’s performance hugs the MSCI World Index within 0.3% every year, congratulations—you’re paying more for the illusion of sophistication. Meanwhile, the only ones truly diversified are the ETF providers raking in your fees.
The Psychological Trap: Why More Feels Safer (But Isn’t)
It’s not just about numbers. The biggest risks of overdiversification in ETF portfolios are psychological. Investors crave action, novelty, and the comfort of “having all bases covered.” The finance industry feeds this with a buffet of choices and fear-driven marketing. The average European investor, bombarded by ETF launches and “must-have” new themes (AI, ESG, frontier markets), ends up in portfolio paralysis.
Let’s talk real money. In France, a 2022 survey by Amundi showed that ETF investors who owned more than 10 funds underperformed their broad benchmark by an average of 0.6% per year due to overlapping exposures, excess rebalancing, and, yes, fees. Over a 20-year horizon, that’s a 12% drag relative to the humble two-ETF combo (global equity + euro bonds) that’s the backbone of an all-weather portfolio.
To Be Fair: The Case for Selective Diversification
Let’s steelman the counterargument: Not all diversification is bad. Owning just one fund exposes you to index construction risk, currency mismatches, or regulatory quirks. There are legitimate cases for adding a targeted ETF—say, a Eurozone government bond tracker as explored here, or a niche inflation hedge as we examined in our inflation hedge ETF analysis.
During the 2022 energy shock, investors who had a slice of global commodities ETFs outperformed vanilla equity/bond mixes by up to 7% in EUR terms. That’s real diversification. But here’s the difference: these were deliberate, high-conviction tilts—not “just one more ETF” for the sake of variety.
True diversification means exposure to genuinely different drivers of risk and return—not simply owning more pieces of the same pie.
So yes, there are real risks to having too little diversification. But most European ETF portfolios are running headlong into the opposite trap: collecting funds like stamps, with diminishing results.
How to Spot—and Fix—Overdiversification
Here’s your litmus test: If you can’t explain why each ETF deserves a slot in your portfolio—and how it adds distinct, non-overlapping exposure—you’re already overdiversified.
- Check for overlap: Use tools like JustETF’s portfolio overlap calculator. If two funds share more than 75% of holdings, merge or drop one.
- Consolidate by geography and asset class: One global equity ETF, one Eurozone bond ETF, and (optionally) one inflation hedge is enough for 90% of investors. Anything beyond that needs a clear, evidence-based rationale.
- Watch your fees: Every 0.1% counts. With European ETF TERs now as low as 0.07% (see Degiro’s commission-free ETF list), there’s no excuse to overpay for closet indexing.
- Resist “theme” creep: Themed or sector ETFs can be useful bets—but only in moderation, and not as a substitute for core exposures. Don’t use “AI” or “ESG” ETFs to make yourself feel diversified if they simply buy more Microsoft and Alphabet.
For a step-by-step guide on getting your allocations right, see our breakdown on top mistakes in building European all-weather portfolios.
The Future Is Lean: Less Is More for European ETF Investors
I’ll say it plainly: In the coming years, the best-performing European ETF portfolios will be the simplest ones. With fees heading to zero and most broad markets increasingly correlated, obsessing over “maximum diversification” is a mug’s game. Instead, the next wave of smart investors will keep it ruthlessly simple—two or three sharply chosen funds, rebalanced with discipline, and zero closet indexing.
Here’s my bet: By 2028, the average cost of a well-diversified, two-ETF portfolio in Europe will fall below 0.10%—and those who shed their unnecessary funds now will enjoy 10-15% higher cumulative returns over the next decade compared to the “ETF collectors.” Your future self will thank you.
Disclaimer: This article reflects the author's opinion and is for educational purposes only. It does not constitute financial advice. Always do your own research before making investment decisions.