Portfolio a alokace
How to Diversify Without Over-Diversifying
Key takeaways
- Diversification reduces unsystematic risk, but can never eliminate systematic market risk.
- After roughly 20–30 uncorrelated stocks, each additional holding brings diminishing diversification benefit.
- A single global ETF covering thousands of stocks essentially solves diversification without needing more funds.
- Adding more funds purely for the feeling of diversification increases costs, complexity, and the chance of mistakes.
- Sector or thematic ETFs can paradoxically reduce diversification by doubling exposure.
Diversification is the allocation of capital across multiple assets so that the loss of one does not mean the loss of the entire portfolio. It works — but it has limits. Beyond a certain point, every fund added brings minimal benefit and maximum complexity.
Where Diversification Stops Helping
Classic research in modern portfolio theory showed that unsystematic risk — the risk specific to a company or sector — declines as more holdings are added. After approximately 20–30 uncorrelated stocks, the effect is nearly exhausted. What remains is systematic market risk, which cannot be eliminated through diversification. Adding more funds won't change that.
One ETF as Complete Diversification
A global index ETF covering the entire world via the MSCI World or All-World index holds thousands of stocks from dozens of countries and hundreds of industries. From an equity diversification standpoint, it is a practically complete solution. Why such an index forms a strong foundation is explained in the article What is a stock index.
Signs of Over-Diversification
A portfolio is over-diversified if:
- You have ten or more ETFs, but half of them hold overlapping stocks
- You've added sector ETFs that double exposure — a technology ETF on top of a portfolio with S&P 500
- You don't know what your funds actually hold — the portfolio is unreadable
- Transaction costs of rebalancing exceed the benefit of the additional fund
When to Add Another Asset Class
Adding bonds, gold, or a REIT ETF makes sense if these asset classes have low correlation with equities and genuinely change the risk profile of the portfolio. How correlation works is explained in the article on asset correlation. Adding them purely to make the portfolio "look diversified" is a mistake.
FAQ
How many funds is the right number for a portfolio?
It depends on your goals, but two to five funds cover the needs of most investors. One global equity ETF and one bond ETF are a sufficient foundation for long-term investing.
What is over-diversification?
A state in which you have too many funds that overlap with each other or add only minimal diversification benefit. It increases costs and complexity without actually reducing risk.
How do I know whether my ETFs are duplicated?
Compare fund holdings on the provider's website or on justETF. If two funds hold a large share of the same stocks, one is redundant. Sector ETFs are typically heavily represented in broad indices.