When and How to Rebalance Your Investment Portfolio

A portfolio is not a static entity. Left unmanaged, the mix of assets inside it shifts constantly as different markets rise and fall at different rates. A portfolio designed with a 60% equity, 40% bond allocation might drift to 75% equity, 25% bonds after a strong stock market run — and suddenly you are exposed to far more risk than you intended or planned for.

Rebalancing is the process of returning a portfolio to its target allocation. It sounds simple, and the concept is — but the implementation involves decisions about timing, tax, costs, and currency that matter significantly over a long investment horizon.

Why Portfolios Drift and Why It Matters

In a year when global equities return 15% and bonds return 2%, your equity weight grows. Your risk profile has silently changed. If equities then fall sharply — as they periodically do — you are more exposed than your plan intended.

The same logic works in reverse. A portfolio that has underallocated to equities following a sell-off, because no rebalancing occurred, misses subsequent recovery. Rebalancing enforces the discipline of trimming what has done well and adding to what has underperformed — a systematic version of "buy low, sell high" that removes emotion from the decision.

Long-term evidence suggests that systematic rebalancing contributes modestly but consistently to risk-adjusted returns — not because it improves raw performance, but because it keeps the portfolio aligned with the risk level that generates the expected return.

The Main Rebalancing Strategies

Calendar rebalancing — review and rebalance at a fixed interval, typically annually (often at the tax year end or calendar year end). This is simple to implement and gives you a predictable schedule. The downside is that it may trigger rebalancing when drift is minimal, incurring unnecessary transaction costs.

Threshold rebalancing — rebalance when any asset class drifts more than a set percentage from its target, commonly 5%. If equities should be 60% and they drift to 66%, you rebalance. This is more responsive to market moves but requires ongoing monitoring.

Hybrid approach — check the portfolio annually but only rebalance if drift exceeds a threshold. This combines simplicity with efficiency and is the approach adopted by many professional portfolio managers.

For most private investors, an annual review with a 5% threshold trigger is a sensible starting point.

Tax Implications of Rebalancing

This is where rebalancing gets genuinely complex for taxable accounts.

In a tax wrapper (ISA, pension/SIPP, offshore bond) — rebalancing is tax-free. You can buy and sell freely within the wrapper without triggering capital gains tax or income tax on the transactions. For investors who hold their portfolios predominantly within tax-advantaged wrappers, rebalancing is relatively straightforward.

In a general investment account (GIA) — every sale of an overweight asset is a potentially taxable disposal. If your equity funds have appreciated significantly, selling some to rebalance may trigger a CGT liability. The CGT annual exempt amount (£3,000 in 2026/27) provides some headroom, but for a large portfolio with significant embedded gains, even modest rebalancing can generate a meaningful tax bill.

Strategies for managing tax in a GIA:

• Rebalance using new contributions — rather than selling overweight assets, direct new investment into underweight ones. This avoids triggering disposals entirely and is the most tax-efficient approach where contributions are ongoing.
• Use bed-and-ISA — sell assets in the GIA and immediately repurchase them inside an ISA (within the annual ISA allowance). You crystallise a gain, but future growth is then sheltered. The annual ISA allowance (£20,000) limits how much can be moved each year.
• Harvest losses — if some holdings are underwater, sell them to crystallise losses that can be offset against gains from rebalancing elsewhere.
• Time large disposals carefully — if you are rebalancing in a year of low income (perhaps after retiring, or before a salary increase), you may fall into a lower CGT rate band. The 2026/27 CGT rates on investment assets are 18% (basic rate) and 24% (higher rate) — a meaningful difference.

Rebalancing Without Selling: The Contribution Method

For investors making regular contributions — whether monthly savings or annual lump sums — the most elegant rebalancing approach is to direct all new money into whichever asset class is most underweight relative to the target.

This achieves gradual rebalancing without generating any disposals and therefore no CGT. Over time, contributions systematically correct drift. Where contributions are too small relative to the portfolio size to correct drift meaningfully within a year, some selling will still be necessary — but the contribution method reduces the amount that needs to be sold.

Currency Rebalancing: A Complication for International Investors

An internationally mobile investor typically holds assets in multiple currencies: GBP investments in an ISA, USD assets in a US brokerage account, EUR property or cash. Currency movements add a layer of complexity that purely domestic investors do not face.

Consider a portfolio target of 50% GBP assets, 30% USD assets, 20% EUR assets. If sterling weakens significantly against the dollar, the USD assets' GBP value increases — the portfolio may now show 40% USD and 40% GBP, even if the underlying asset prices in local currency have been unchanged.

The question is: is this drift intentional or unintentional?

• If you hold USD assets specifically as a dollar hedge, currency drift may be part of the strategy.
• If you chose asset class allocations without specific currency views, the currency drift is unintentional noise that should be corrected.

Currency rebalancing also has tax implications: a gain on a currency movement in a GIA is, in principle, a taxable event. HMRC treats gains from currency movements as falling within CGT, though in practice, tracking currency gains embedded in foreign-denominated fund holdings is complex.

For internationally mobile investors who expect to spend in multiple currencies in retirement, the target allocation itself should reflect the anticipated currency of expenditure — not just a global benchmark weighting.

How Often Is Too Often?

Over-rebalancing — rebalancing every month or every time drift exceeds 1% — is usually counterproductive. Transaction costs (even in low-cost platforms these exist in the form of spreads), potential CGT, and time invested in monitoring can outweigh the marginal benefit of keeping the portfolio tightly on target.

Academic research on rebalancing frequency suggests that annual rebalancing captures most of the benefit of continuous rebalancing, at a fraction of the cost. Monthly rebalancing adds very little benefit over annual rebalancing in most simulated portfolio scenarios.

For actively managed multi-asset portfolios managed by a professional, more frequent rebalancing may be appropriate — but that is the manager's responsibility, not yours.

Documenting Your Rebalancing Policy

Before your first rebalancing, write down:

• Your target allocation (each asset class as a percentage).
• Your rebalancing trigger (annual, or threshold-based, or both).
• Your tax strategy for each account (contribution-first in taxable accounts; free rebalancing in wrappers).
• Who is responsible for monitoring and executing (you, your adviser, or a discretionary manager).

Having a written policy removes the temptation to make ad hoc decisions based on market sentiment. The most common mistake in portfolio management is making a rebalancing decision based on a market view ("equities look expensive, so I won't rebalance into them") rather than the original plan.

How Global Investments Can Help

Rebalancing across multiple accounts, in multiple currencies, in multiple jurisdictions is not a trivial exercise. Global Investments helps clients establish portfolio construction and rebalancing policies that are consistent with their risk tolerance, tax position, and long-term financial objectives. For portfolios managed on a discretionary basis, rebalancing is handled systematically as part of the portfolio management service, with full transparency on what is being done and why. Speak to our advisers to review your current portfolio's alignment with your objectives.