Portfolio Rebalancing: When and How to Do It
A portfolio built with a specific equity-to-debt mix rarely stays that way. Markets move unevenly, and the allocation an investor started with can look very different a few years later, without a single new rupee being added. Rebalancing is the process of bringing that mix back in line with the original plan. This guide covers why drift happens, two common frameworks for deciding when to act, and the costs of rebalancing too often.
This article is educational and explains general portfolio-management concepts. It is not investment advice. Rebalancing decisions depend on individual goals, risk tolerance, and tax situations, so consider consulting a certified financial advisor before acting.
How Allocations Drift Without Any New Investment
Suppose an investor starts with a portfolio split 60% in equity funds and 40% in debt funds. If equities go on to outperform debt over the following two or three years, the equity portion of the portfolio grows faster in value than the debt portion. Even though the investor never changed a single holding, the portfolio might now be 72% equity and 28% debt simply because one asset class grew faster than the other.
This is allocation drift. It matters because the original 60/40 split was presumably chosen to match a certain risk tolerance and time horizon. A drifted 72/28 split is a meaningfully riskier portfolio than the one the investor originally intended to hold. The reverse can also happen: if equities underperform debt for a stretch, the portfolio can drift toward being more conservative than intended, potentially under-shooting long-term growth goals. Drift is not a sign that something went wrong with the underlying funds; it is a mechanical consequence of different assets growing at different rates.
Two Common Rebalancing Triggers
Rather than deciding on an ad hoc basis, most systematic approaches to rebalancing rely on one of two triggers, or a combination of both.
- Calendar-based rebalancing: The portfolio is reviewed and reset back to its target allocation at fixed intervals, for example once a year on a specific date, or semi-annually. The appeal of this approach is its simplicity and predictability. An investor always knows when the next review will happen and does not need to track markets in between. The drawback is that a calendar date may arrive when drift is minimal (making the rebalancing unnecessary) or may miss a period where drift became large well before the scheduled check-in.
- Threshold-based rebalancing: The portfolio is rebalanced whenever an allocation drifts beyond a predefined band, for example more than 5 percentage points away from its target. Under this approach, a 60/40 target portfolio would trigger a rebalance if equity exposure rose above 65% or fell below 55%. This method responds to actual market movement rather than the calendar, so it can catch large drifts sooner, but it requires more frequent monitoring to know when a threshold has been crossed.
Some investors combine both: they check the portfolio on a fixed schedule (say, quarterly) but only act if the drift also exceeds a chosen threshold at that check-in. This limits both unnecessary transactions and the risk of large, unmonitored drift.
The Cost of Rebalancing Too Often
Rebalancing is not free, and treating it as a frequent, low-friction adjustment can quietly erode returns. Two costs are worth weighing before every rebalancing decision.
- Exit loads: Many mutual fund schemes charge an exit load, a fee deducted if units are redeemed within a specified holding period, often around one year. Rebalancing by selling units that are still within this window means paying that load on top of any other costs, directly reducing the amount that gets reinvested.
- Capital gains tax: Selling fund units to rebalance is a redemption event, and any gains realized are subject to capital gains tax based on how long the units were held. Frequent rebalancing can mean repeatedly realizing gains at less favorable short-term rates instead of allowing gains to qualify for long-term tax treatment, and it can also mean paying tax earlier than necessary on gains that would otherwise have kept compounding.
For example, suppose an investor rebalances every time equity allocation drifts by even 1 percentage point. Because normal market volatility alone can cause moves of that size within weeks, this could mean redeeming and reinvesting many times a year, each time potentially triggering exit loads and short-term capital gains, while achieving little practical difference in risk compared to a wider band. A wider threshold, such as 5 percentage points, or a fixed annual review, tends to reduce these frictional costs considerably while still keeping the portfolio reasonably close to its target allocation.
Rebalancing Without Selling
One way to reduce the tax and exit-load drag of rebalancing is to adjust future contributions rather than sell existing units. If equity has grown to be overweight, an investor can direct new SIP installments or lump-sum additions toward debt funds until the allocation moves back toward target, avoiding a redemption event entirely. This approach works best when there is enough ongoing new investment to meaningfully shift the mix within a reasonable time frame; for large, one-off drifts, some amount of selling may still be necessary.
Before deciding which funds to trim or add to, it can help to see how much overlap exists between the funds already held, since two funds with very similar underlying stock holdings offer less real diversification than their separate labels suggest. Reviewing this with the portfolio overlap tool before rebalancing can clarify whether a portfolio is genuinely diversified across asset classes and fund styles, or just spread across multiple funds that behave similarly.
Frequently Asked Questions
- How often should a portfolio be rebalanced?
- There is no single fixed answer, as it depends on individual goals and how much drift an investor is comfortable tolerating. Common frameworks include reviewing annually on a fixed date, or acting only when an allocation moves beyond a chosen band such as 5 percentage points from target. Many investors combine both approaches.
- Does rebalancing guarantee better returns?
- No. Rebalancing is primarily a risk-management discipline that keeps a portfolio aligned with an intended asset mix, rather than a technique for maximizing returns. In some periods it can reduce returns compared to letting a winning asset class run, and in others it can help by systematically trimming an asset class after a large rally.
- Is rebalancing only about equity versus debt?
- Equity-to-debt is the most common axis discussed, but drift can also occur within equity itself, for example between large-cap, mid-cap, and small-cap allocations, or across sectors and geographies. The same calendar-based or threshold-based logic can be applied to these finer-grained allocations.
- Can rebalancing be done without redeeming units?
- Yes, in many cases. Directing new investments, such as SIP installments, toward the underweight asset class can gradually restore the target allocation without triggering exit loads or capital gains tax. This works best when drift is moderate and there is enough new investment flowing in to close the gap within a reasonable period.