What it means
Every portfolio starts with a target allocation, for example 60% shares and 40% bonds, chosen to match the owner's tolerance for loss. Markets then do what they do, and after a strong run in shares the same portfolio might be 68% shares, carrying far more risk than the owner signed up for.
Rebalancing pulls it back to the plan. The behavioural value is what makes the discipline hard.
Rebalancing forces an investor to sell what has been performing well and buy what has been performing badly, which feels wrong at exactly the moment it matters most. Written rules exist precisely so the decision is not made in the heat of a rally or a crash.
There are two common approaches. Calendar rebalancing checks the portfolio at fixed intervals such as quarterly or annually, while threshold or band rebalancing acts only when an asset class drifts more than an agreed amount from target, often around 5 percentage points.
Many investors combine the two, checking on a schedule but trading only if a band has been breached. Costs and taxes shape how often it is sensible to act.
Every trade carries dealing costs, and in a taxable account selling winners can trigger a capital gains bill, so aggressive rebalancing can destroy more value than the risk control is worth. Directing new contributions and dividends into the underweight asset is often a cheaper way to achieve the same drift correction.
One misconception is worth flagging: rebalancing is not designed to raise returns. Over long periods it usually reduces both volatility and, slightly, total return, because it repeatedly trims the fastest-growing asset.
The payoff is a portfolio whose risk stays close to what the owner intended.
In practice
Real-world examples.
Example
A company pension scheme rebalances quarterly under a written policy. After a strong equity quarter its trustees sell $4,200,000 of shares and buy government bonds, restoring the 55/45 split their funding strategy requires.
Example
A private investor uses new savings instead of trades. Rather than selling appreciated shares and paying capital gains tax, she directs her $1,500 monthly contribution entirely into bonds until the target weights are restored.
Example
A charity endowment discovers its property allocation has drifted from 10% to 16% because listed markets fell while appraisal-based property values did not. The investment committee agrees to sell part of the property fund over six months, accepting that illiquid assets cannot be rebalanced quickly.
Think of it
“Rebalancing puts your portfolio back to target-resetting your mix.
Formula
Calculation
Current weight = Asset value / Total portfolio value. Trade required = (Target weight x Total portfolio value) - Current asset value.
An investor starts the year with $1,000,000 split 60/40: $600,000 in shares and $400,000 in bonds. Their policy is to rebalance whenever any holding drifts more than 5 percentage points from target.
Over the year shares gain 30%, taking them to $600,000 x 1.30 = $780,000. Bonds gain 2%, taking them to $400,000 x 1.02 = $408,000. The portfolio is now worth $780,000 + $408,000 = $1,188,000.
Current share weight = $780,000 / $1,188,000 = 0.6566, or 65.7%. That is 5.7 percentage points above the 60% target, so the band has been breached and a trade is due.
Target share value = 0.60 x $1,188,000 = $712,800. The trade required is $712,800 - $780,000 = -$67,200, meaning sell $67,200 of shares.
The proceeds go into bonds, which become $408,000 + $67,200 = $475,200. Checking the result: $475,200 / $1,188,000 = 0.40, exactly the 40% target, and shares sit at $712,800 / $1,188,000 = 60%.Case study
Seen in the real world.
Alderpine Foundation is an illustrative, fictional charitable endowment used to show what happens when rebalancing is neglected. Its investment policy specified 50% shares, 30% bonds and 20% alternatives, but the committee met only twice a year and had waved through a long equity rally without acting.
By the time a 30% equity market fall arrived in the fictional timeline, shares had drifted to 67% of the $80,000,000 portfolio, which is $13,600,000 more equity exposure than the policy allowed. That excess alone cost the foundation about $4,100,000, and it had to cut its annual grant budget by $400,000 to protect the capital base.
The committee's response was to adopt a 5 percentage point band with a monthly check performed by the custodian, and to rebalance using incoming donations wherever possible. The illustrative lesson is that rebalancing rules are cheap to write and expensive to skip, and their value only becomes visible in the year everything falls.
Watch out
Common mistakes.
- Rebalancing too often. Monthly trading on small drifts racks up dealing costs and tax with almost no risk benefit compared with quarterly or band-based rules.
- Expecting rebalancing to increase returns. Its purpose is to keep risk at the intended level, and in strongly trending markets it will usually cost a little performance.
- Abandoning the policy during a crash. The moment rebalancing feels most uncomfortable, buying the asset that has fallen, is the moment it does the most work.
Questions
People also ask.
How often should a portfolio be rebalanced?
Annually or quarterly with a drift band of around 5 percentage points suits most long-term investors, and more frequent action rarely justifies the cost.
Does rebalancing trigger tax?
In a taxable account selling appreciated assets can create a capital gain, which is why many investors rebalance inside tax-sheltered accounts or use new contributions instead.
Can illiquid assets be rebalanced?
Only slowly, because property, private equity and infrastructure cannot be traded on demand, so policies for these usually set wide bands and long correction periods.
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