What is diversification, and how much is enough?
Diversification means not putting all your money into one company, sector or country, so a single failure can't wipe you out. Spreading across many holdings cancels out the risk unique to any one of them. A single global tracker fund already holds thousands of companies worldwide, which is usually plenty. Piling on extra funds brings smaller and smaller benefit.
Why does putting everything in one company go wrong?
Diversification is a simple idea with an unglamorous name: don't put all your money into one company. Even a business that looks rock-solid today can hit trouble no one saw coming, whether a scandal, a failed product, or a debt it can't repay. Companies do sometimes fall all the way to zero, and shareholders can be left with nothing.
The catch is that you can rarely tell in advance which company that will be. Spreading your money across many holdings means no single failure can sink you. You give up the daydream of picking the one big winner, and in return you remove the nightmare of picking the one big loser.
How does spreading across sectors and countries help?
Individual companies aren't the only thing that can wobble. Whole sectors go through hard spells: banks in a credit crunch, oil firms when the price of crude slumps, tech when a boom cools. If all your money sits in one industry, a bad year for that industry is a bad year for you.
Countries can stall too. A single national economy might drift for a decade while others grow. Spreading across sectors and across countries means that when one corner of the world is struggling, another may be doing fine, and the calmer parts cushion the rougher ones.
How much diversification is actually enough?
Here's the reassuring part. You don't need to assemble hundreds of shares by hand. One broad global tracker fund already holds thousands of companies across dozens of countries in a single, low-cost product. In one purchase you own a slice of firms on almost every major exchange, weighted roughly by their size.
Research on diversification points to a clear pattern: most of the risk unique to individual companies disappears once you hold a few dozen well-spread shares. A global tracker sails far past that point, which is why, for a lot of beginners, one fund does the entire job.
Can you be too diversified?
So can you overdo it? In a sense, yes, not by owning too many companies, but by owning too many overlapping funds. Ten funds that each hold the same familiar global giants don't give you ten times the protection; they give you the same protection with ten times the paperwork and, often, higher combined fees.
This is the diminishing-returns part. Once you already hold a broad global fund, each extra fund you bolt on tends to add cost and complexity while doing very little for your actual spread. More funds and genuinely more diversification are not the same thing.
A worked example
Imagine two people each put £10,000 to work. Aisha puts all £10,000 into one company. Ben spreads his £10,000 across a global tracker holding 3,000 companies, so each company is worth about £3 of his money. Then that one company collapses to zero. Aisha loses her entire £10,000. Ben loses roughly £3, a rounding error, because the other 2,999 companies carry on as before. Same shock, wildly different outcome. That gap is what diversification gives you.
Common questions
How many shares do you need to be diversified?
Research suggests most of the risk tied to individual companies fades once you hold roughly 20 to 30 well-spread shares across different sectors. A single global tracker fund holds thousands of companies in dozens of countries, so it clears that bar many times over. For most beginners, one broad fund does the whole job.
Does diversification remove all risk?
No. It removes the risk unique to any single company or sector, but not the risk that whole markets fall together, since a global downturn drags almost everything down at once. Diversification smooths the bumps from individual failures; it does not promise you'll never see your total value drop.
Can you be too diversified?
In a way, yes. Owning ten funds that all hold the same giant companies adds cost and admin without real extra protection; that's duplication, not diversification. Beyond a broad global fund, each extra holding does less and less. More funds is not automatically more safety for your money.
Where to next
General information to help you understand investing, not advice about your situation. Figures are illustrative and the rules can change - always check gov.uk or your provider for the latest.