Rebalancing, and how often is enough

Portfolios drift away from their target allocation as assets perform differently. Rebalancing returns them, and the details matter less than the fact of doing it.

What it does

The primary function is risk control rather than return enhancement.

A portfolio left alone through a long equity bull market becomes progressively more equity-heavy, and therefore riskier than intended, precisely when valuations are highest.

Rebalancing sells what has risen and buys what has not, maintaining the intended risk level.

There is sometimes a return benefit as well, from systematically selling high and buying low across asset classes, but the evidence for a reliable rebalancing bonus is weaker than commonly claimed and depends heavily on the assets involved.

Risk control is the defensible justification.

How often

Research comparing rebalancing frequencies generally finds small differences between reasonable approaches.

Annual rebalancing performs comparably to more frequent schedules in most studies, with lower transaction costs and less administration.

Rebalancing very frequently — monthly, or continuously — generally reduces returns slightly through costs and by cutting short momentum, without materially improving risk control.

Rebalancing very rarely — every several years — allows substantial drift.

Annual, or when allocations drift beyond a defined band, are both defensible. The choice between them matters much less than having a rule.

Threshold rebalancing

The alternative to calendar-based.

Rebalance when an asset class drifts more than a defined percentage from target — five percentage points is a commonly used band.

This responds to actual drift rather than to the calendar, which means more action during volatile periods and none during calm ones.

A combined approach — check annually, act only if outside the band — captures most of the benefit with minimal effort.

Doing it tax-efficiently

The main practical consideration in taxable accounts, where selling triggers gains.

Rebalance in tax-advantaged accounts first. Trades there have no tax consequence, and for many people the tax-advantaged portion is large enough to accomplish the whole adjustment.

Use cash flows. During accumulation, direct new contributions to the underweight asset. In retirement, take withdrawals from the overweight one.

This rebalances gradually without any selling, and for many people it is sufficient on its own.

Direct dividends deliberately rather than automatically reinvesting them in the same holding.

Pair with loss harvesting where losses are available to offset gains.

Accept some drift in taxable accounts where the tax cost of correcting it exceeds the benefit. Precision is not the objective.

The difficult part

Rebalancing requires selling what has done well and buying what has done badly, which is behaviourally uncomfortable.

After a substantial equity decline, rebalancing means buying more equities at exactly the moment it feels least advisable.

This is when the discipline matters most and when it is least likely to be followed.

The practical defence is a written policy with a defined rule, decided in advance, so that the action is mechanical rather than a fresh judgement made under stress.

What not to do

Rebalance based on a market view. Deciding not to rebalance because you think equities will keep rising converts a risk control process into market timing.

Rebalance into individual positions. The process is about asset classes, not about topping up a favourite holding.

Ignore it entirely for a decade. The most common failure, and it generally results in an unintentionally aggressive portfolio at exactly the wrong stage of life.

Changing the target

Distinct from rebalancing and worth separating.

Adjusting the target allocation itself is a strategic decision that should be driven by changed circumstances — approaching retirement, a change in required return, a change in capacity to bear loss.

Changing the target because of a market view is market timing wearing different clothes, and it usually happens after a decline, which is the worst possible time.

Rebalancing across accounts

A practical point for households with several accounts.

The allocation that matters is the household total, not the allocation within each account.

Which means the target can be achieved by holding entirely different things in different accounts — bonds concentrated in a tax-deferred account, equities in a Roth and in taxable holdings.

This allows both asset location efficiency and tax-free rebalancing, since the adjustments happen inside the sheltered accounts.

It requires a single view of the total, which is why a simple spreadsheet listing every holding is worth maintaining.

General information only, not financial advice. Consult a qualified adviser about your own situation.