What Diversification Can and Cannot Do

Diversification is the closest thing investing has to a free lunch. By holding a mix of assets whose values do not move in lockstep, you can smooth the journey without necessarily accepting lower long-term returns. If one part of your portfolio is having a poor year, another may be holding steady or even gaining.

What it cannot do is remove risk. In a sharp, broad market fall, most assets drop together. Diversification cushions the blow; it does not stop you being hit. Anyone who tells you otherwise is selling something. The aim is not to avoid losses altogether, but to make sure no single setback can derail your plans.

Spread Across Asset Classes, Not Just Shares

Asset classes tend to behave differently because they are driven by different things: company profits, interest rates, inflation, supply and demand. A sensible starting point for most UK households is a mix along these lines:

• Global equities — the long-term growth engine, but the most volatile part of the pot.
• Bonds and gilts — loans to governments and companies. They often steady a portfolio when shares wobble, though they can fall too when interest rates rise.
• Cash — held in an easy-access account or premium bonds. Useful for emergencies and money you will need within three to five years, but it loses buying power to inflation over long periods.
• Property — whether a buy-to-let or a property fund. Illiquid and expensive to sell, so best kept as a minority holding.
• Gold and commodities — a small allocation, perhaps 5% or less, can add a genuinely different source of return.

The right split depends on your time frame. Money you need in two years should not be in shares at all; money you will not touch for twenty years can afford to be equity-heavy.

Think Globally, Not Just About the FTSE

UK investors have a stubborn habit of holding mostly UK companies, often because the names feel familiar. But the UK stock market makes up only a small slice of the global total, and it is heavily concentrated in a handful of sectors such as banking, energy and consumer staples. A portfolio biased to Britain is effectively a bet on those industries and on sterling.

Spreading across North America, Europe, Japan, Asia-Pacific and emerging markets gives you exposure to thousands of companies, different currencies and different economic cycles. A single global tracker fund can do this job for a fraction of a percent in annual charges, which is hard to beat for simplicity.

Regional diversification works best when you resist the temptation to chop and change. Selling out of an underperforming region after a bad year is a reliable way to lock in losses and miss the recovery.

Diversify Within Each Asset Class Too

Holding one fund is not diversification. If that fund tracks the FTSE 100, you own 100 large UK companies and nothing else. Look inside your holdings:

• Company size — large, mid and smaller companies behave differently across the cycle.
• Sectors — technology, healthcare, utilities and financials rarely peak at the same time.
• Geography and currency — overseas earnings give you a natural hedge against a weak pound.
• Style — growth companies and value companies take turns to lead, sometimes for years at a time.

A common trap is overlap. If you hold five global funds, you may own the same handful of technology giants five times over, creating a concentration you never intended. Check the top ten holdings of each fund before adding another.

Keep Costs, Tax Wrappers and Rebalancing in View

Diversification is only worthwhile if the costs do not eat the benefit. Platform fees typically range from about 0.15% to 0.45% a year, and fund charges from 0.05% for a simple tracker to well over 1% for an actively managed fund. Ten funds at 0.8% each is a very different proposition from five at 0.2%.

Use your allowances properly. An ISA shelters up to £20,000 a year from income tax and capital gains tax, and a pension adds tax relief on the way in, though you cannot access it until later. Spreading assets between an ISA, a pension and a general dealing account gives you flexibility about when and how you take money out.

Finally, rebalance. If shares have had a strong run, they may now make up a larger share of your portfolio than you intended, quietly raising your risk. Many investors check once or twice a year and top up lagging areas, or trim back when a holding drifts more than five percentage points from target. Doing this automatically removes emotion from the decision and quietly enforces the discipline of selling high and buying low.

Start with a mix you can hold through a bad year without panicking. That, more than any clever fund choice, is what keeps a portfolio intact.