Why Rebalancing During Market Downturns Is More Valuable Than You Think

Rebalancing is the most consistently undervalued practice in long-term investing. It requires no market timing, no manager selection skill, and no proprietary analysis. It demands only that investors maintain a target asset allocation — a defined percentage in equities, bonds, alternatives, and cash — and periodically return to that target when market movements have pushed the actual allocation away from it.

In practice, rebalancing is deceptively difficult. It requires selling assets that have recently risen (the winners) and buying assets that have fallen (the losers). During a market downturn — when equities are down 25%, financial news is alarming, and client confidence is shaken — rebalancing means buying more equities at a moment when many investors are contemplating selling everything. This is why disciplined rebalancing is valuable: it systematically implements buy-low-sell-high mechanics in a way that removes the need for market timing judgement.

The Mechanics: Why Rebalancing Works

Consider a portfolio with a target allocation of 60% global equities and 40% global bonds. Over the course of a year, equities rise 20% while bonds rise 3%. The portfolio now holds approximately 64% equities and 36% bonds. Without rebalancing, the investor has drifted into a riskier portfolio than intended — their equity exposure has grown, their drawdown risk has increased, and in a subsequent market decline they will lose more than expected.

Rebalancing back to 60/40 means selling some of the equities (which have risen) and buying bonds (which have lagged). If the equity market subsequently corrects, the rebalanced investor participates less in the decline.

The same logic applies in reverse during a downturn. If equities fall 30% and bonds rise 5%, the portfolio might be sitting at 47% equities and 53% bonds. Rebalancing means buying equities (which have fallen, are now cheaper) and selling bonds (which have risen). This is the "buy low" moment that most investors intellectually understand but emotionally fail to execute.

Research — including work by Vanguard's investment strategy team — emphasises that the primary purpose of rebalancing is to control risk and keep a portfolio aligned with its intended allocation, rather than to maximise return. Because higher-returning assets (typically equities) tend to grow as a share of an un-rebalanced portfolio, rebalancing can modestly reduce long-run nominal return while meaningfully reducing volatility and drawdown risk — improving risk-adjusted returns. The value of rebalancing lies in this discipline and risk control, not in a guaranteed return premium.

Threshold vs Calendar Rebalancing

There are two primary approaches to triggering a rebalance:

Calendar rebalancing: rebalance at predetermined intervals — monthly, quarterly, or annually. Annual rebalancing is typically sufficient for long-term portfolios; more frequent rebalancing increases transaction costs without proportionate benefit. Quarterly may be appropriate for larger portfolios where the absolute value of drift is significant.

Threshold (band) rebalancing: rebalance only when the allocation to any asset class drifts beyond a predefined tolerance band — for example, rebalance equities when they drift more than 5 percentage points from target. This approach responds to actual portfolio drift rather than calendar dates and tends to trigger rebalancing more often in volatile markets (exactly when it is most valuable) and less often in stable markets.

Research suggests threshold rebalancing (with bands of 5–10%) slightly outperforms calendar rebalancing on a risk-adjusted basis, though both are substantially better than no rebalancing. In practice, many discretionary managers use hybrid approaches: a calendar trigger combined with a maximum tolerance band that prompts action between scheduled reviews.

The cost consideration: rebalancing involves transaction costs — brokerage fees and bid-offer spreads. For small portfolios or portfolios with high transaction costs, calendar rebalancing annual or semi-annual is usually sufficient to avoid excessive friction. For direct equity portfolios with no dealing charges (e.g., within certain platforms), threshold rebalancing can be implemented more frequently without cost penalty.

Tax Considerations During a Rebalancing Event

This is where discipline must be combined with intelligence. Rebalancing within a taxable General Investment Account (GIA) triggers capital gains tax on sales. For a UK investor rebalancing in 2026, CGT applies at 18% (basic rate) or 24% (higher/additional rate) on net gains above the annual exempt amount (£3,000 for 2026/27).

A mechanical rebalancing programme that ignores tax will erode returns unnecessarily. Tax-efficient rebalancing techniques include:

Using new contributions: the most tax-efficient rebalancing method is directing new investment into underweight asset classes rather than selling overweight ones. If equities are overweight, new cash contributions go to bonds; the portfolio moves toward target without triggering disposals.

Dividend and income redirection: if dividends or interest income from the portfolio are collected as cash rather than automatically reinvested, they can be directed to underweight asset classes before triggering selling.

Selling within allowances: use the annual CGT exempt amount (£3,000 in 2026/27) each tax year to sell some of the overweight position tax-free, accumulating gains without a tax event.

Bed and ISA / Bed and SIPP: selling a GIA holding that has risen and repurchasing it within an ISA or SIPP wrapper eliminates future growth from CGT scope. The disposal crystallises a gain (taxable) but moves the investment into a tax-sheltered environment. This is most valuable for assets expected to grow substantially in future.

Tax-loss harvesting: selling GIA holdings that are currently in a loss position to generate an allowable loss that offsets gains from rebalancing disposals.

Rebalancing within wrappers first: selling inside an ISA or SIPP generates no CGT event. Rebalancing should prioritise wrappers first, using GIA selling only when wrapper capacity is insufficient.

Psychological Barriers to Rebalancing

Understanding why rebalancing is so difficult psychologically is important for investors who want to implement it successfully:

Recency bias causes investors to extrapolate recent performance. After a 30% equity decline, buying more equities feels like catching a falling knife. After a strong run, selling equities feels like leaving money on the table.

Loss aversion makes the pain of selling a declining asset feel worse than the rational portfolio management calculus suggests it should. Buying into a falling market feels like adding losses.

Media and peer pressure: market downturns generate intense negative media coverage that reinforces the feeling that buying equities is irrational.

Institutional investors — pension funds, sovereign wealth funds — rebalance mechanically regardless of sentiment because their mandates require it. This discipline is precisely what allows them to buy during crises, effectively transferring wealth from panic sellers to disciplined long-term holders. For private investors, either internalising the rebalancing discipline or delegating to a discretionary manager who will implement it without emotional interference is the practical solution.

Rebalancing with New Contributions

For investors still in accumulation phase, using new contributions to rebalance rather than selling existing positions is the most efficient approach, as it avoids:

• CGT triggers in GIA
• Dealing costs on both sides of a trade
• The psychological discomfort of selling

A simple annual process: before adding new funds, compare actual allocation to target allocation, and direct the new contribution entirely (or proportionally) to the most underweight asset class. Over time, this keeps the portfolio close to target without generating taxable events.

For investors contributing to ISAs and SIPPs regularly, this process happens naturally within tax-free wrappers — maximising ISA and pension contributions before investing in GIA is therefore not just about tax efficiency on the new money, but about reducing the need for future taxable rebalancing.

Automatic Rebalancing Tools

Several UK investment platforms offer automatic rebalancing as a feature of their managed portfolio or model portfolio services. Vanguard's LifeStrategy funds, for example, automatically rebalance to their target allocations. Multi-asset funds (discussed elsewhere on this site) achieve the same effect via internal rebalancing within the fund structure, avoiding all CGT events for fund investors.

For investors managing direct portfolios through platforms such as Hargreaves Lansdown, AJ Bell, or Interactive Brokers, automatic rebalancing is available through some portfolio management tools and model portfolio services.

Investments can fall as well as rise. Rebalancing does not guarantee positive returns and does not protect against market losses. Tax rules change, and the tax treatment of rebalancing events depends on individual circumstances. This guide does not constitute personal financial advice or tax advice. Investors should seek independent professional advice before implementing investment strategies.

How Global Investments Can Help

Disciplined rebalancing is a core element of our discretionary portfolio management service. We monitor client allocations against target across all accounts, use contributions and dividends to rebalance efficiently, and coordinate rebalancing actions with your tax position to minimise unnecessary CGT triggers. Contact us to discuss how we can help you implement systematic, tax-efficient rebalancing.