Rebalancing Doesn't Have to Mean Selling Everything

Over time, the investments that do well quietly take over your portfolio. If you started with a simple split — say 80% in global shares and 20% in bonds — a strong run for shares could leave you at 88% shares without you lifting a finger. That is drift, and it means your portfolio is now carrying more risk than the plan you signed up to.

Rebalancing is simply nudging those weights back towards your targets. The version most people picture involves selling the winners and buying the laggards, which sounds like effort, can trigger tax, and often means paying dealing charges twice over. The gentler alternative is to do the work with money that was already heading into or out of your portfolio.

Why Cash-Flow Rebalancing Suits Most Beginners

If you pay into an ISA or a pension every month, or you take a regular income from your pot in later life, you already own the perfect rebalancing tool. Instead of spreading new money evenly, you point it at whatever has fallen behind. Nothing is sold, so nothing is crystallised for tax, and you avoid two sets of dealing charges to shift the same amount of cash.

• New contributions: send your monthly or annual top-up to the asset that sits below its target.
• Withdrawals: when you need cash, take it from whatever sits above its target.
• Dividends and interest: reinvest them into the underweight holding rather than the one that paid them.
• Windfalls: a bonus, an inheritance or a fresh ISA allowance each April is a chance to close a large gap in one move.

The beauty of this approach is that it is automatic and boring, which is exactly what you want. You are not making a judgement about which asset will do better next year. You are following a rule that keeps your risk roughly where you decided it should be.

Work Out Where You Actually Are

You cannot correct a gap you have not measured, so start with a simple one-page snapshot. Twice a year is plenty for most people, and once a year is perfectly respectable.

• List each account separately — workplace pension, SIPP, stocks and shares ISA, and any general investing account.
• Note your target percentage for each broad asset class: shares, bonds, and perhaps property or cash.
• Note the current value of each holding and what percentage of the total it represents.
• Write down the difference. Anything more than about five percentage points from target is worth acting on.

If you hold a ready-made multi-asset fund, the provider rebalances internally and you can largely ignore this. The cash-flow method matters most when you hold separate funds or a handful of ETFs.

A Worked Example

Suppose you hold £30,000 in an ISA. Your target is 60% shares and 40% bonds, so you want £18,000 in shares and £12,000 in bonds. After a good couple of years, shares have grown to £19,800 and bonds sit at £10,200 — that is 66% and 34%.

Shares are £1,800 overweight and bonds are £1,800 underweight. Rather than selling shares, you simply direct your next £1,800 of contributions into bonds. If you invest £300 a month, six months of payments does the job without a single sale. If instead you are drawing £150 a month from the ISA, take the whole lot from shares: ten months of withdrawals brings the mix back into line.

Larger drift, or a big lump sum, can be fixed in a single afternoon. The arithmetic is the same — you are just working with bigger numbers.

When You Might Still Need to Sell

Cash-flow rebalancing has limits, and you should know them rather than pretend otherwise.

• You have stopped contributing. If you are fully retired and drawing a small income, your withdrawals may not be large enough to correct a big gap. Sell a little from the overweight side.
• Drift has run far ahead. If shares are 15 percentage points above target, new money alone may take years to fix it. A partial sale is the sensible answer.
• Your plan has changed. A move from 80% shares to 50% is a redesign, not a rebalance, and it will need real transactions.
• Tax wrappers matter. Sales inside an ISA or pension are not subject to capital gains tax, so do the selling there first. Sales in a general account can trigger a bill, and the annual exempt amount is far smaller than it once was.

The practical trick is to hold your bonds, or whatever you use to dampen volatility, inside your ISA or pension wherever possible. That way, when you do need to sell, you can do it without a tax consequence.

Build a Simple Annual Routine

Choose a date you will remember — the start of the tax year, or your birthday — and spend twenty minutes on it. Check your target weights against your time horizon and your attitude to risk, and ask yourself whether anything has genuinely changed. If not, leave the targets alone and just steer your contributions.

Rebalancing is not about squeezing out extra returns. It is about keeping the risk you are taking honest. Done with new money, it costs you nothing, takes minutes, and quietly keeps your portfolio aligned with the goals you set when you started.