One fund vs three funds

The case for one fund

A single globally diversified index fund or ETF — something like one tracking the FTSE All-World or MSCI World index — already holds thousands of companies across dozens of countries. It is diversified across sectors, geographies, and company sizes. It requires one annual cost, one purchase, and no rebalancing.

For most long-term investors building wealth over 10, 20, or 30 years, this is enough. The data does not suggest that adding a second or third fund to a broadly diversified global fund produces meaningfully better outcomes. What it adds is complexity, and complexity tends to work against investors over time by creating more decisions, more tinkering, and more opportunities to make behavioural mistakes.

The best portfolio is not the theoretically optimal one — it is the one you can actually maintain without second-guessing it for decades.

When a second fund genuinely helps

There are legitimate reasons to add a second holding:

• Adding bonds. A global equity fund holds only shares. Adding a bond fund reduces overall volatility and can make the portfolio easier to hold through severe market falls. This matters more as you get older or as your timeline shortens.
• Tilting toward income. If you want your portfolio to generate dividend income (rather than growth), adding a dividend-focused ETF alongside a growth ETF serves a genuine purpose.
• Reducing UK home bias. Some UK investors deliberately add a UK-specific fund alongside a global one to slightly overweight the UK. This is a preference, not a requirement.

In each of these cases, the second fund does something meaningfully different from the first. That is the test worth applying: does this holding add genuine diversification or capability, or does it just add more of the same?

The overlap problem

The most common mistake is building what feels like a diversified multi-fund portfolio but is actually a highly overlapping one. Three popular examples:

• A global ETF + a US ETF + an S&P 500 ETF: the US market represents 60–65% of the global index. These three funds share enormous overlap in their top holdings.
• A FTSE All-World ETF + an MSCI World ETF: these track slightly different but heavily overlapping universes. The difference is marginal; the complexity is real.
• A technology ETF added to a global fund: global indexes are already heavily weighted toward technology companies. You are concentrating, not diversifying.

Use the planning calculators to check whether your holdings are genuinely spreading risk or creating unintentional concentration.

A reasonable two or three fund structure

If you want to go beyond one fund deliberately, a structure that makes sense:

• 80% global equity ETF (e.g. FTSE All-World or MSCI World) — growth engine
• 20% global bond ETF (e.g. iShares Global Aggregate Bond) — stabiliser

Or for those comfortable with equity-only:

• 85% global developed market ETF
• 15% emerging markets ETF (to add explicit emerging market exposure beyond what some global funds include)

Beyond three funds, the marginal benefit of additional holdings becomes very difficult to justify for a normal long-term investor.