Rebalancing Your Portfolio Without Chasing Trends

Why Portfolios Drift in the First Place

You set up a sensible mix — perhaps 60% in shares, 40% in bonds and cash — and then life carries on. What many investors don't realise is that a portfolio left alone doesn't stay at 60/40. It quietly reshapes itself. If global equities have a strong couple of years, that 60% slice can easily become 70% or more. Nothing has gone wrong, exactly, but your risk level has crept upwards without you choosing it.

That drift matters more as you approach and move through retirement. A portfolio that was designed to fund twenty-five years of withdrawals becomes considerably more fragile if it has quietly turned into a growth-heavy one. Rebalancing is simply the habit of nudging things back to the mix you originally chose — and it is one of the few genuinely useful things you can do in a quiet week.

Choose a Rule Before You Need It

The hardest part of rebalancing isn't the maths. It's the psychology. Every instinct tells you to sell what has done well and buy what has lagged, which feels exactly backwards. The way round this is to decide your rule in advance, in writing, when markets are calm and you have no strong feelings either way.

Most investors are well served by one of two approaches, and either is perfectly respectable:

• Calendar rebalancing: you check your allocation on a fixed date — say, the first week of April each year, after the tax year has turned. If anything is out of line, you fix it. If not, you do nothing and go and enjoy the spring.
• Threshold rebalancing: you act only when an asset class drifts more than a set amount from target, commonly five percentage points. So a 60% equity allocation would trigger a review if it reached 65% or fell to 55%.

A blend works well for many people: check annually, but also act sooner if a big market move pushes you past your threshold. What matters is that the rule is fixed and boring. A rule you renegotiate whenever it becomes inconvenient isn't a rule.

Rebalance With New Money Where You Can

Here's the practical trick that saves both cost and admin. You don't have to sell anything to rebalance. If your equity allocation has fallen below target and you're still contributing to a pension or stocks and shares ISA, direct the next few months of contributions towards equities until the balance is restored. In drawdown, do the reverse: take your income from whichever part of the portfolio has grown above its target weight.

This approach has real advantages. It keeps trading costs negligible, avoids crystallising gains you don't need to crystallise, and it feels far less dramatic than a wholesale reshuffle. It is also very well suited to the monthly saver, who can rebalance gradually over a year or so without ever making a large single decision.

Keep an Eye on Tax Wrappers and Costs

If you do need to sell, the order in which you do it matters. Assets held inside an ISA or a pension can be switched without triggering a capital gains tax liability, so rebalancing inside those wrappers is usually the place to start. A general investment account is less forgiving, and it's worth using your annual capital gains allowance carefully if you need to sell there.

Costs deserve a mention too. Frequent small trades can quietly eat into returns, and some platforms charge for each deal. Rebalancing roughly once a year, or when thresholds are breached, keeps trading to a minimum. If you hold funds rather than individual shares, a single switch within the same provider is often the simplest and cheapest route.

Ignore the Headlines, Follow the Plan

The whole point of a rebalancing schedule is that it removes the need to have an opinion about what happens next. When a sector is soaring, your rule tells you to trim it — not because you think it's about to fall, but because it has grown beyond the risk you signed up for. When something is unloved, your rule may tell you to top it up. That's the discipline working as intended.

Trends are seductive precisely because they are visible in hindsight and noisy in the moment. A rebalancing plan lets you sidestep the question of whether this time is different. If you find yourself wanting to abandon the rule because of a particular news story, that's usually a signal to leave the portfolio alone for a fortnight.

A Few Sensible Grounds for Breaking the Rule

Rules serve you, not the other way round. There are legitimate reasons to revisit your target allocation — just not market noise. Consider a review if:

• Your circumstances have genuinely changed — retirement is closer, a spouse has died, long-term care costs are on the horizon, or you have inherited a sum that alters your plans.
• Your capacity to bear losses has shifted, for instance because a larger share of your income now comes from the portfolio.
• Your target allocation no longer reflects the life you're actually living, rather than the one you imagined a decade ago.

Those are reasons to rethink the plan itself, ideally with a regulated adviser, and then rebalance towards the new target. A turbulent week on the markets is not one of them.

Done well, rebalancing is undramatic: a short annual check, a few adjustments, and a portfolio that still matches the risk you chose. That quiet consistency is worth more than any amount of clever timing.