“Don’t put all your eggs in one basket” is one of the oldest pieces of investment advice, and one of the most important. Diversification means spreading your money across different investments so that a fall in one doesn’t wreck your entire portfolio. It’s one of the few tools that can reduce risk without necessarily reducing your long-term return potential, which is why it’s often called the closest thing to a free lunch in investing.
But diversification is more complicated than simply owning lots of things. Many investors believe they’re well diversified when they’re not, and today’s global stock market indices are more concentrated than they’ve been in decades. This guide explains how diversification works, the different types, how correlation affects it, how many holdings you need, the risks of hidden concentration, how to diversify a UK portfolio and the mistakes to avoid.
Table of Contents
What Is Diversification?
A Simple Definition
Diversification is the practice of spreading your investments across different assets, companies, sectors, countries and investment styles to reduce the impact of any single investment performing badly.
Why It Works
Different investments respond differently to economic events. When some fall, others may rise, hold steady or fall less. Combining them can produce smoother returns overall.
What Diversification Can and Can’t Do
| Diversification Can | Diversification Can’t |
|---|---|
| Reduce the impact of one company failing | Prevent losses in a broad market crash |
| Smooth out portfolio returns | Guarantee profits |
| Lower overall volatility | Eliminate all risk |
| Improve risk-adjusted returns | Protect against every type of shock |
Two Types of Risk: What Diversification Targets
Specific (Unsystematic) Risk
The risk tied to a single company or sector, such as a product failure, scandal or poor management. Diversification can reduce this risk significantly.
Market (Systematic) Risk
The risk that affects almost all investments, such as recessions, interest rate changes, inflation shocks or geopolitical events. Diversifying within shares can’t remove this, but diversifying across different asset types can help.
| Risk Type | Examples | Reduced by Diversification? |
|---|---|---|
| Specific risk | Company profit warning, fraud, lost contract | Yes, largely |
| Sector risk | Tech sell-off, oil price crash | Yes, across sectors |
| Country risk | Political or economic problems in one country | Yes, across regions |
| Market risk | Global recession, financial crisis | Partly, across asset classes |
The Role of Correlation
What Is Correlation?
Correlation measures how closely two investments move together, on a scale from −1 to +1:
| Correlation | Meaning | Diversification Benefit |
|---|---|---|
| +1 | Move in exactly the same direction | None |
| 0 to +0.5 | Move somewhat independently | Moderate |
| 0 | No relationship | Strong |
| Negative | Tend to move in opposite directions | Very strong |
Why Correlation Matters
Owning ten technology shares may feel diversified, but if they all respond to the same factors, they may rise and fall together. True diversification combines investments with lower correlations.
Correlations Can Change
Correlations aren’t fixed. During market crises, many assets can fall together. In 2022, for example, rising interest rates hit both shares and bonds at the same time, reducing the usual cushioning effect bonds provide. Good diversification considers how investments might behave in different economic conditions, not just in normal times.
The Main Types of Diversification
1. Across Asset Classes
Combine different types of investments:
- Shares (equities): Growth potential, higher volatility
- Bonds: Income and stability, usually less volatile
- Cash: Safety and liquidity
- Property: Income and potential inflation protection
- Commodities and gold: May behave differently from shares and bonds
- Alternatives: Infrastructure, private equity, absolute return strategies
2. Within Asset Classes
Spread your money across many companies or bond issuers rather than a handful.
3. Across Sectors
Different industries perform well at different times:
| Sector | Tends to Do Well When |
|---|---|
| Technology | Innovation and growth are strong |
| Consumer staples | Economy slows (people still buy essentials) |
| Healthcare | Defensive, steady demand |
| Energy | Oil and gas prices rise |
| Financials | Interest rates rise (in some cases) |
| Utilities | Investors seek stable income |
| Industrials | Economic expansion and investment |
4. Across Countries and Regions
Different economies grow at different speeds and face different risks. Global diversification can include the UK, US, Europe, Japan, Asia Pacific and emerging markets.
5. Across Company Sizes
Large, mid-sized and small companies can perform differently. Smaller companies often offer higher growth potential with higher risk.
6. Across Investment Styles
- Growth: Companies expected to grow faster than average
- Value: Companies trading below their perceived worth
- Income: Companies paying high dividends
- Quality: Strong balance sheets and stable profits
7. Across Currencies
Holding investments in different currencies can reduce reliance on the pound, though it also introduces currency risk.
8. Across Time
Investing regularly over months and years, rather than all at once, spreads your entry points and reduces the risk of investing everything at a market peak.
How Many Investments Do You Need?
Individual Shares
Research suggests that holding a few dozen shares across different sectors can significantly reduce company-specific risk. Many investors aim for at least 20–30 holdings, though more may be needed for broader diversification across countries and styles.
Funds Make It Easier
A single global index fund can hold thousands of companies across dozens of countries, offering far more diversification than most investors could achieve by buying individual shares.
| Approach | Typical Holdings | Diversification Level |
|---|---|---|
| A few individual shares | 1–10 | Very low |
| Portfolio of individual shares | 20–40 | Moderate |
| UK index fund | Hundreds | Good within UK |
| Global index fund | Thousands | Broad |
| Multi-asset fund | Thousands plus bonds | Broad across assets |
Hidden Concentration: The Modern Diversification Challenge
Global Indices Are More Concentrated Than Ever
Many investors buy a global index fund and assume they’re well diversified. But global indices have become heavily weighted towards the US and a handful of very large technology companies.
The change has been dramatic. In January 2006, the US accounted for 48.6% of MSCI World, with Japan (11.3%) and the UK (11.4%) providing meaningful diversification. By August 2026, the US weight had risen to 70.6%, while Japan had fallen to 5.7% and the UK to 3.5%.
A Handful of Companies Dominate
Single-company concentration has also risen. MSCI notes that the top 10 constituents of the MSCI World Index make up more than a quarter of its total weight — a fourfold increase in 15 years. The U.S. now represents over 70% of the index, while information technology alone accounts for more than a quarter.
The trend has accelerated recently. MSCI data shows that between April 30, 2025, and July 31, 2026, the weight of the 10 largest constituents climbed from 26.7% to 38.1% in the MSCI Emerging Markets Index, 32.3% to 36.7% in the MSCI USA Index and 20.5% to 24.2% in the MSCI ACWI® Index.
To put it in perspective, Schroders found that the five biggest companies in the US now carry a similar index weight to the next five biggest countries combined.
| Concentration Measure | Figure |
|---|---|
| US weight in MSCI World (Aug 2026) | 70.6% |
| UK weight in MSCI World (Aug 2026) | 3.5% |
| Japan weight in MSCI World (Aug 2026) | 5.7% |
| Top 10 weight in MSCI ACWI (Jul 2026) | 24.2% |
| Top 10 weight in MSCI USA (Jul 2026) | 36.7% |
| Top 10 weight in MSCI Emerging Markets (Jul 2026) | 38.1% |
Why This Matters
Concentration isn’t automatically bad. These companies have grown because of strong earnings and innovation. But it means a global tracker is more exposed to US technology and AI-related shares than many investors realise. MSCI warns that risk concentration — where a small subset of holdings drives most volatility — adds another layer that weight-based reporting often obscures.
Ways to Reduce Concentration
- Add an ex-US fund: For example, an MSCI World ex US fund. AJ Bell notes that the MSCI World ex US index is less concentrated with the top 10 holdings accounting for just 13% of the benchmark, compared with 28% for the market-cap weighted version.
- Use equal-weight funds: Each company has a similar weighting, reducing the influence of the largest firms
- Add regional funds: UK, Europe, Japan, Asia Pacific or emerging markets
- Include smaller companies: Small and mid-cap funds offer different exposures
- Hold other asset classes: Bonds, property, infrastructure or gold
Home Bias: Too Much or Too Little UK?
What Is Home Bias?
Home bias is the tendency to invest heavily in your own country’s market. UK investors have traditionally held a large share of UK shares, even though the UK makes up only a small portion of global markets.
Pros and Cons of UK Exposure
| Pros of Holding UK Shares | Cons of Too Much UK Exposure |
|---|---|
| No currency risk for sterling investors | UK is a small share of global markets |
| Strong dividend culture | Less exposure to fast-growing tech sector |
| Familiar companies | Concentration in sectors like banks, energy and mining |
| Potential valuation opportunities | Ties wealth to one economy |
Finding Balance
Many UK investors hold a global core with a modest UK allocation for income and currency balance. The right mix depends on your goals, income needs and views.
Diversifying With Bonds
Why Bonds Matter
Bonds often (though not always) behave differently from shares and can provide income and stability.
Bond Diversification
- Government bonds (gilts): Lower credit risk
- Corporate bonds: Higher yields, more risk
- Index-linked bonds: Protection against inflation
- Global bonds: Spread across countries (often currency-hedged)
- Short, medium and long duration: Different sensitivity to interest rate changes
The Current Environment
With the Bank of England raising Bank Rate to 4% in November 2026 and UK CPI inflation at 3.5% in September, bond yields are higher than in the low-rate era, which can make bonds more attractive as both income and diversifiers. But inflation-linked and shorter-duration bonds may be worth considering if inflation stays high.
Diversification With Other Assets
Property
Property funds and REITs can provide income and exposure to real estate, though some property funds can suspend dealing during market stress.
Gold and Commodities
Gold has sometimes held value during market turmoil and inflation, though it pays no income and can be volatile.
Infrastructure
Infrastructure funds invest in assets like energy networks, transport and utilities, often offering steady, inflation-linked income.
Cash
Cash provides stability and liquidity, and keeps you from being forced to sell investments during downturns.
High-Risk Assets
Crypto and other speculative assets are sometimes promoted as diversifiers, but they’re extremely volatile. If you hold them, keep them to a small amount you can afford to lose.
Example Diversified Portfolios
Simple Two-Fund Portfolio
| Holding | Balanced Allocation |
|---|---|
| Global equity index fund | 60% |
| Global bond index fund (GBP hedged) | 40% |
Concentration-Aware Portfolio
| Holding | Allocation |
|---|---|
| Global equity index fund | 40% |
| Global ex-US equity fund | 15% |
| UK equity fund | 10% |
| Global small-cap fund | 5% |
| Global bond fund (hedged) | 20% |
| Index-linked gilts | 5% |
| Cash | 5% |
One-Fund Option
A multi-asset fund provides an instant mix of shares and bonds, rebalanced automatically.
All portfolios are illustrative only and not personal advice. Investments can fall as well as rise.
Diversification vs “Diworsification”
When Diversification Goes Too Far
Owning too many overlapping funds can create complexity without adding real diversification. This is sometimes called “diworsification.”
Signs of Over-Diversification
- Several funds tracking similar indices
- Many active funds holding the same large companies
- Higher total fees for little extra benefit
- Difficulty tracking and managing your portfolio
How to Avoid It
- Check fund factsheets for overlapping holdings
- Use portfolio analysis tools on your platform
- Keep your portfolio simple with a clear purpose for each holding
Rebalancing: Keeping Diversification on Track
Why Rebalance?
Over time, strong-performing assets grow to dominate your portfolio. For example, a 60/40 portfolio can drift to 70/30 after a strong run for shares, increasing your risk.
How to Rebalance
- Review once or twice a year
- Rebalance when allocations drift by a set amount (for example, 5 percentage points)
- Direct new contributions towards underweight assets
- Rebalance inside ISAs and pensions to avoid capital gains tax
Diversifying Beyond Your Portfolio
Think About Your Whole Financial Life
Your job, home and pension are also part of your overall financial picture:
- Job concentration: Avoid holding too many shares in your employer
- Property: If most of your wealth is in your home, consider investing elsewhere
- Income streams: Side income or multiple revenue sources can add resilience
- Tax wrappers: Spread savings across ISAs, pensions and general accounts for flexibility
UK Investor Protections
Diversify Across Providers Too
FSCS protection for eligible investments is £85,000 per person per authorised firm, and cash deposits are protected up to £120,000 per banking licence. If you have large sums, consider spreading them across providers.
Use FCA-Authorised Firms
Check the FCA Register before using any investment platform or adviser.
Common Diversification Mistakes
Owning Many Similar Investments
Lots of holdings don’t equal diversification if they all move together.
Assuming a Global Tracker Is Fully Diversified
Global indices are now heavily weighted towards the US and a small number of tech giants.
Too Much Home Bias
Over-reliance on UK shares limits exposure to global growth.
Ignoring Bonds and Cash
An all-share portfolio may be too volatile for many investors.
Chasing Past Winners
Diversification can feel frustrating when one asset outperforms, but it protects you when leadership changes.
Never Rebalancing
Portfolios drift towards higher risk over time.
Over-Diversifying
Too many funds add cost and complexity without real benefit.
Diversification Checklist
| Action | Done? |
|---|---|
| Hold a mix of asset classes suited to your goals | ☐ |
| Spread shares across many companies and sectors | ☐ |
| Invest across different countries and regions | ☐ |
| Check concentration in US and top holdings | ☐ |
| Review your level of UK home bias | ☐ |
| Include bonds and cash for stability | ☐ |
| Avoid overlapping funds | ☐ |
| Invest regularly over time | ☐ |
| Rebalance at least once a year | ☐ |
| Spread large sums across providers | ☐ |
Final Thoughts
Diversification is one of the most powerful tools for managing investment risk. By spreading your money across asset classes, companies, sectors, countries, company sizes, styles and time, you reduce the impact of any single investment going wrong and create a smoother path towards your long-term goals.
But diversification needs regular attention. Today’s global indices are far more concentrated than in the past, with the US making up around 70% of MSCI World and the top 10 companies accounting for a quarter or more of many major indices. Check what your funds actually hold, consider adding ex-US, equal-weight, smaller company or bond exposure if you want broader balance, avoid unnecessary overlap and rebalance regularly. Diversification won’t prevent every loss, but it can help you stay invested and on track through whatever markets bring.
Frequently Asked Questions
1. What is diversification in investing?
Diversification means spreading your money across different investments, such as shares, bonds, sectors and countries, to reduce the impact if one performs badly.
2. Is a global index fund fully diversified?
It offers broad diversification, but global indices are now heavily concentrated, with the US making up around 70% of MSCI World and the top 10 companies a large share of the index.
3. How many funds do I need to be diversified?
Many investors can achieve good diversification with just one to four funds, such as a global equity fund, a bond fund and possibly regional or smaller company funds.
