Risk and diversification

Three different things get called risk, and confusing them is how people end up in the wrong portfolio.

"How much risk should I take?" is the question everyone asks and almost nobody answers well, because the word covers at least three different things that pull in different directions.

Three kinds of risk

Volatility is how much the value moves around. It's what people usually mean, it's what gets measured, and it's the least important of the three if you don't need the money soon. A portfolio that falls 20% and recovers has cost you nothing except discomfort.

Permanent loss is money that doesn't come back — a single company going bust, a fund closing, an investment that was never sound. Diversification is the defence, and it works.

Shortfall risk is ending up with less than you needed. It's the one people underrate, and it's the reason "safe" isn't always safe. Cash never falls in nominal terms and reliably loses purchasing power over decades. Someone thirty years from retirement holding everything in cash has eliminated volatility and taken on a near-certainty of falling short.

The mistake is optimising for the first and ignoring the third.

Three questions, not one

Good risk assessment separates things that get bundled together:

Attitude to risk — how you feel about your investments falling. Psychological, personal, and largely stable.

Capacity for loss — how much you could actually afford to lose without it changing your life. Financial and objective. Someone with a large guaranteed pension and no debts has high capacity regardless of how they feel; someone whose entire retirement depends on one pot has low capacity even if they're relaxed about it.

Need to take risk — how much return your plan actually requires. Someone who'll comfortably meet their goals with a 3% return has no need to reach for 7%, however comfortable they'd be with it. Taking risk you don't need is a real error.

The right answer sits at the intersection of all three, and the binding constraint is whichever is lowest.

Time horizon does most of the work

The single biggest determinant of how much volatility you can sensibly accept is when you need the money.

Under three years: cash. Not because shares are bad, but because there isn't time to recover from a fall, and the sequence you happen to get matters more than the average.

Three to ten years: a mix, weighted by how firm the date is and how flexible you could be if markets were down when you arrived.

Over ten years: volatility becomes much less relevant and shortfall risk becomes the main enemy.

Most people's money has several horizons at once — a house deposit in two years, retirement in twenty-five — and those should be treated as separate pots with separate answers rather than blended into one middling portfolio.

What diversification actually does

Spreading money across investments that don't move together reduces how much the whole falls when one part does badly. It does not remove risk, and in a serious crisis correlations tend to rise — many things fall at once.

Diversify across:

Asset classes — shares, bonds, property, cash
Geography — the UK is a small part of the world market
Sector — technology, healthcare, financials, energy
Individual holdings — no single company large enough to hurt you
Currency, which for a UK investor with global holdings is a real exposure in both directions

Home bias is worth naming. UK investors typically hold far more UK equity than the UK's share of global markets justifies. It feels safer because the names are familiar. Familiarity isn't diversification, and the UK market is heavily weighted towards a small number of sectors.

The shares and bonds mix

The main lever is the split between growth assets and defensive ones. More in shares means higher expected returns and bigger falls along the way; more in bonds means the reverse.

Old rules of thumb — subtract your age from 100 for your equity percentage — are crude and have aged poorly given longer retirements and different bond yields. Use them as a sanity check, not a method.

Bonds aren't risk-free either. 2022 demonstrated that when interest rates rise sharply, bonds fall, and they can fall at the same time as shares — which is precisely when you were relying on them not to.

The part that decides everything

The best portfolio is the one you'll actually stick with.

A theoretically optimal allocation that you abandon in a bad month is worse than a cautious one you hold for thirty years. Most of the gap between what investments return and what investors receive comes from behaviour — buying after things have gone up, selling after they've gone down.

If a 30% fall would make you sell, don't build a portfolio that can fall 30%, whatever the risk questionnaire says. That's covered further in Time in the market.

This article is for general education only and isn't personal advice. The right level of risk depends on your circumstances, your timescale and your objectives.