You own several shares, a few exchange-traded funds (ETFs) and perhaps a bond fund. Your investment account looks varied. But what if most of those holdings depend on the same technology companies, the same country or falling interest rates?
A long list of investments can hide a surprisingly narrow set of risks.
Portfolio diversification means spreading investments across assets whose returns are not all driven by the same forces. The aim is to reduce the damage that a single company, sector or market can cause to your finances. It cannot guarantee a profit or prevent losses across the portfolio.
“The useful question is therefore: what risks am I spreading, and which ones am I repeating?”
How is diversification different from asset allocation?
Asset allocation is the division of your portfolio between asset classes, such as shares, bonds and cash. Diversification concerns the variety of exposures both between those classes and within them.
An investor might allocate part of their portfolio to bonds but buy only one company's debt. That adds an asset class while leaving substantial exposure to a single borrower. Holding many companies' shares spreads company risk but still leaves the portfolio exposed to a broad stock market decline.
FINRA distinguishes three related decisions: choosing an asset allocation, diversifying the holdings within it and rebalancing when the mix changes. Each serves a different purpose.
Which risks can diversification reduce?
Diversification is particularly useful for reducing company-specific risk: the possibility that one business suffers a setback, such as a failed product, accounting scandal or loss of a major customer.
Consider two hypothetical portfolios, each worth CHF 20’000. One holds a single company. The other holds 20 companies in equal proportions.
If that company falls by 50% while every other holding remains unchanged:
| Portfolio | Exposure to the affected company | Portfolio loss |
|---|---|---|
| One company | CHF 20’000 | CHF 10’000, or 50% |
| 20 equally weighted companies | CHF 1’000 | CHF 500, or 2.5% |
This illustration isolates one company shock. It excludes fees, taxes and currency effects and assumes no movement in the other shares. It is not a forecast or a recommendation to hold 20 stocks.
The outcome changes if all 20 companies face the same problem. Twenty banks, for example, may share exposure to deteriorating credit conditions. Spreading money between them reduces dependence on one bank but leaves substantial sector risk.
Diversification also has limits against systematic risk: forces that affect much of the market, such as a recession or financial crisis. Many investments can fall together.
Why does correlation matter?
Correlation describes how closely two investments' returns move together over a measured period. A positive correlation means they tend to move in the same direction; a negative correlation means they tend to move in opposite directions. A correlation near zero indicates little linear relationship.
Diversification benefits depend partly on these relationships. Two investments do not have to move in opposite directions to help spread risk. They can still contribute if their movements are sufficiently different.
However, historical correlation is an observation, not a promise. Its value depends on the period, return frequency and currency used, and it can change as economic conditions change.
Shares and bonds illustrate this limitation. High-quality bonds may help cushion an equity decline in some circumstances. But inflation and rising interest rates can put pressure on both asset classes at once. Vanguard's research discusses how inflation and economic shocks influence the relationship between their returns.
The practical lesson is to consider several scenarios. Ask what might happen to your holdings during weaker growth, higher inflation or a sharp change in interest rates.
Where should you look for different exposures?
Diversification has several dimensions. None should be considered in isolation.
| Dimension | What to examine | What it cannot remove |
|---|---|---|
| Companies and issuers | Dependence on individual businesses or borrowers | Broad market losses |
| Sectors | Exposure to different industries and customers | Economy-wide shocks |
| Countries and regions | Reliance on one market or political environment | Global crises |
| Asset classes | Different roles for shares, bonds and cash | Simultaneous losses or inflation risk |
| Bond characteristics | Issuers, credit quality and maturity | Default and interest rate risk |
| Currencies | Exposure relative to your future spending currency | Unfavourable exchange rate movements |
For a Swiss investor, familiar domestic businesses may feel reassuring. Familiarity alone does not establish that they provide different sources of risk.
International investments can broaden exposure, but introduce additional considerations, including political, regulatory and currency risks. The SEC's investor guidance highlights these trade-offs.
Currency deserves particular attention. If you measure your wealth in Swiss francs, a foreign investment's return also depends on exchange rate movements. Buying a fund through a CHF trading line does not, by itself, remove the currency exposure of its underlying assets. Check whether the share class is explicitly currency-hedged and understand the costs and limits of that hedge.
Can several ETFs leave you concentrated?
Yes. Different fund names can conceal similar underlying holdings.
Imagine owning a global equity ETF, a US large-company ETF and a technology ETF. You might also hold a few technology shares directly. Depending on the funds' composition, the same businesses could appear in all four places.
FINRA recommends examining fund holdings alongside individual securities to identify this kind of overlap. It also notes that narrowly targeted funds can create concentration rather than broad diversification.
Here is a hypothetical calculation. Suppose 60% of your portfolio is in Fund A, which allocates 5% to Company X. Another 20% is in Fund B, which allocates 10% to that company. You also hold 5% of the portfolio in Company X directly.
Your total exposure to Company X is:
(60% × 5%) + (20% × 10%) + 5% = 10%.
This assumes the remaining holdings contain no Company X exposure. The calculation shows why counting funds can miss concentration. The underlying weights matter.
A broadly invested ETF can spread exposure across many securities. A sector or thematic ETF may serve a deliberate investment view, but its contribution should be assessed against what you already own.
Check underlying holdings and portfolio weights. Different products may repeat the same exposure.
Explain what an investment contributes, such as broader equity exposure, liquidity or a particular bond allocation.
Different assets can still fall together. Plan for losses as well as potential benefits.
How can you review your own portfolio?
Start with the goal. Money needed for a near-term expense has a different job from money invested for retirement decades away. A diversified equity portfolio can still be unsuitable for a short-term commitment.
Then review your exposures in five steps:
- List holdings and weights. Include investments across accounts rather than reviewing each account separately.
- Inspect funds' underlying assets. Identify repeated companies, sectors and markets.
- Consider your wider finances. Employer shares, pension investments and property may add exposures that your trading account does not show.
- Test plausible setbacks. Consider an equity decline, higher interest rates or a stronger Swiss franc. These are scenarios, not predictions.
- Review costs and complexity. An additional holding should provide a clear benefit worth its fees and administration.
Your income matters too. Someone whose salary and employer shares depend on the same company could face employment and investment losses together. That connection deserves attention even if the rest of their account appears varied.
Why does diversification need maintenance?
Market movements change portfolio weights. Successful investments can gradually become larger sources of risk.
Rebalancing means adjusting holdings towards a chosen allocation. Investors can review the mix at scheduled intervals or when weights move beyond limits set in advance. The SEC describes selling overweight holdings, buying underweight holdings and redirecting new contributions as possible approaches. Transaction costs and tax consequences also matter. [5]
Rebalancing does not guarantee better returns. Its purpose is to keep exposure aligned with the plan. If your goal or financial circumstances change, the plan itself may need reviewing.
Diversification starts with understanding what you own and how your investments behave together. Adding more holdings can reduce dependence on individual companies, but the benefit becomes smaller when those holdings share similar risks.
There is no universal number of investments that makes a portfolio diversified. Look at the underlying companies, sectors, countries and asset classes, then check whether their weights fit your goals and capacity for loss.
A well-diversified portfolio can still fall in value. Its purpose is to reduce reliance on any single investment or market outcome, helping you manage uncertainty with a portfolio you understand.
Frequently asked questions
How many investments do I need?
There is no universal number. Underlying holdings, weights and shared risks matter more than the number of entries in your account.
Can one fund provide diversification?
Yes, within its investment scope. A broad equity fund can spread company exposure, but remains exposed to equity market risk. Check its mandate and holdings.
Does diversification lower potential returns?
It can reduce the gains you would have made by owning only the best performer. It also reduces dependence on identifying that winner in advance.
Is cash useful in a diversified portfolio?
Cash can provide liquidity for planned spending. However, inflation can erode its purchasing power, and cash products have different protections and risks.
Is a portfolio diversified if everything falls together?
It may be. A shared decline does not prove that diversification was absent. Review the size of the losses, the underlying exposures and whether the portfolio still fits your goal.
The content in this article is provided for educational and marketing purposes only. It does not constitute investment advice or financial recommendations.
