How to Rebalance Your Portfolio in a Tax-Efficient Way

Rebalancing is the discipline of periodically restoring your investment portfolio to its target allocation — trimming asset classes that have grown above target and adding to those that have fallen below it. Done consistently, rebalancing maintains the risk profile your portfolio was designed for and enforces a systematic "sell high, buy low" discipline.

The problem is that rebalancing often requires selling assets that have gained in value. In a general investment account (a GIA, sometimes called an unwrapped account), that triggers a Capital Gains Tax (CGT) liability. After the CGT annual exempt amount was cut to £3,000 from 2024/25, even modest rebalancing in an unwrapped portfolio can generate a tax bill.

This guide covers the strategies that allow you to rebalance effectively while minimising the tax cost.

Why Rebalancing Matters — and Why It Creates Tax Problems

A simple example illustrates the drift problem. Suppose your target allocation is 60% equities and 40% bonds. After a strong equity market year, equities have grown to 70% of your portfolio and bonds have shrunk to 30%. Your portfolio is now more volatile than you intended — it will fall harder in a market downturn and recover the way an equity-heavy portfolio does, not the way a balanced portfolio does.

Rebalancing back to 60/40 requires selling equity holdings and buying bond holdings. If the equity holdings you are selling are sitting on significant gains, the sale crystallises those gains and triggers a CGT liability.

In an era of low annual exemption and relatively high CGT rates (24% for higher-rate taxpayers on most assets from October 2024), the tax drag from unmanaged rebalancing can be substantial. The solution is to use a combination of strategies that either avoid triggering CGT at all, or minimise the rate at which gains are taxed.

Strategy 1: Use New Contributions to Rebalance

The simplest and most tax-efficient way to rebalance is to direct new money into underweight asset classes rather than selling overweight ones.

If bonds are underweight, your next pension contribution or ISA contribution goes into a bond fund. If emerging markets are underweight, your next lump sum goes there. Over time — and particularly in the accumulation phase of investing — this "contribution rebalancing" can keep your portfolio close to target without triggering any sales.

This approach works best when:

• You have regular contributions coming in (salary-linked pension contributions, monthly ISA contributions)
• The drift is gradual rather than extreme (a 5% drift is manageable by contributions; a 20% drift may require some selling)
• Your portfolio is growing — if you are in drawdown and taking money out, you need to sell something, and directing withdrawals from overweight assets is the equivalent technique

Strategy 2: Rebalance Inside Tax Wrappers

ISAs and SIPPs (pensions) are completely free from CGT inside the wrapper. You can buy and sell any holding within your ISA or SIPP as many times as you like without any CGT consequence. Rebalancing inside a wrapper is entirely tax-free.

This makes the composition of your wrapper versus your GIA holdings important. Broadly:

• Assets that you expect to grow most (higher equity allocations, higher-volatility positions) are better placed inside wrappers where the gains are sheltered.
• Lower-growth assets (cash, short-duration bonds) are less urgent to shelter — the CGT liability from rebalancing them is smaller.
• Income-producing assets (bond funds, REITs, high-yield equities) are also valuable inside wrappers because the income is sheltered from income tax as well as CGT.

If you have the capacity to increase pension or ISA contributions as part of your rebalancing, do so — each contribution is a tax-free transfer of funds into the shelter.

Strategy 3: Tax-Loss Harvesting

If your portfolio contains positions sitting at a loss, you can sell them to crystallise the loss, which then offsets gains elsewhere in your portfolio.

Tax-loss harvesting works like this: you have sold an overweight equity fund and realised a £10,000 gain. You also hold a bond fund that has fallen in value and is sitting on a £6,000 unrealised loss. Selling the bond fund crystallises the loss, leaving you with a net taxable gain of £4,000. After the £3,000 annual exempt amount, only £1,000 is taxable.

Critically: you can immediately repurchase the same bond fund within your ISA (a "bed and ISA" transaction — see below), so your underlying portfolio allocation is not changed. The tax loss is crystallised; the investment position is maintained inside a better wrapper.

The 30-day rule (bed and breakfasting): if you sell an investment and repurchase an identical one within 30 days in the same account, HMRC ignores the transaction for CGT purposes. To crystallise a genuine loss, you must either wait 31 days, repurchase inside an ISA or pension (which does not trigger the rule), or buy a similar but not identical fund (for example, a different provider's tracker of the same index).

Strategy 4: Bed and ISA

Bed and ISA is one of the most powerful tax-planning tools available to UK investors. It works as follows:

1. You sell a holding in your GIA, crystallising a gain (which may be partly covered by the annual exempt amount or offset by losses).
2. You immediately repurchase the same investment inside a Stocks and Shares ISA, using this year's ISA allowance (up to £20,000 per person per year).
3. All future growth on that holding is now sheltered from CGT and income tax.

The gain on the original sale is unavoidable if the position is in profit, but all future gains are permanently sheltered. For positions with large unrealised gains, using bed and ISA over multiple tax years (up to £20,000 per year per person, or £40,000 for a couple) gradually moves the portfolio into the ISA wrapper.

Some platforms allow same-day or next-day repurchase inside the ISA. Check your platform's process to minimise market risk during the switch.

Strategy 5: Offshore Bond Switching

Offshore investment bonds (also called offshore bonds) are wrappers offered by life insurance companies, typically based in Ireland, Luxembourg, or the Isle of Man. Within the bond, you can switch between different investment funds without triggering a UK tax event. This makes them naturally rebalancing-friendly for unwrapped portfolios — the rebalancing happens inside the bond with no CGT consequence.

Gains on the bond are only taxed (as income rather than as capital gains) when you make a withdrawal. The 5% withdrawal allowance (a non-taxable notional withdrawal of up to 5% of the original investment per year, cumulative) provides a mechanism for taking income without triggering an immediate tax charge.

Offshore bonds are particularly suitable for higher-rate or additional-rate taxpayers who expect to drop to basic rate in retirement, allowing gains to be taxed at 20% rather than 40% or 45% on encashment. They also offer estate planning benefits and can be particularly useful for internationally mobile individuals.

They are not suitable for everyone — lower-rate taxpayers may find that an ISA produces a better long-term outcome.

Strategy 6: Time Gains to Coincide With Lower-Income Years

CGT rates in the UK depend on your marginal income tax position in the year the gain is realised. If your income is below the higher-rate threshold in a given year — because you have retired, taken unpaid leave, or made large pension contributions that reduced your taxable income — the CGT rate may be 18% rather than 24%.

Where possible, timing rebalancing sales to fall in years when your income is lower reduces the marginal rate on the gain. A gain of £20,000 taxed at 18% costs £3,600; the same gain at 24% costs £4,800. Over a portfolio rebalanced over several decades, managing the rate at which gains are taxed materially affects total returns.

The Annual Rebalancing Calendar

A sensible annual calendar for tax-efficient rebalancing might look like:

• January–February: review portfolio drift. Identify positions to rebalance.
• March: use remaining tax-loss harvesting opportunities before the year-end. Maximise ISA contributions before 5 April.
• April–June (new tax year): maximise new ISA allowance. Direct pension contributions to underweight assets.
• Ongoing: monitor for tax-loss harvesting opportunities after significant market moves.

Rebalancing quarterly or annually is generally sufficient for most portfolios — over-trading in search of perfect allocation increases costs and tax drag.

Compliance Note

CGT rates, annual exempt amounts, ISA allowances, and pension contribution limits referenced in this article reflect the position as of 2026 and are subject to change. This article is for general educational purposes and does not constitute financial or tax advice. Individual tax treatment depends on your specific circumstances, and you should take personalised advice before implementing any of these strategies.

How Global Investments Can Help

For investors with significant unwrapped portfolios, developing a structured rebalancing and tax-efficiency plan can save meaningful amounts over time. Our advisers work with clients to map their existing portfolio, identify the most effective wrapper strategy, and coordinate rebalancing in a way that manages both asset allocation and tax exposure. Contact our team to arrange a portfolio review.