If you set a target asset allocation — say, 70% equity and 30% debt — and then never touch it again, that allocation genuinely will not stay at 70/30 on its own. Whichever asset class happens to perform better over time will naturally grow to represent a larger share of your total portfolio, quietly shifting your overall risk level away from what you originally, deliberately intended, without you ever having made an active decision to take on more (or less) risk.
Why This Happens, Concretely
A genuinely strong equity market year can push a portfolio that started at 70/30 to something like 78/22 within just twelve months, purely through equity outperforming debt during that period — nobody actively added more equity exposure; the allocation simply drifted as a mechanical consequence of differential returns. Left unaddressed for several consecutive years of a strong equity run, a portfolio originally built for a moderate risk tolerance can gradually end up concentrated at a risk level closer to genuinely aggressive — often right around the time, close to a specific financial goal's deadline, when you'd actually want less risk in the portfolio, not more, precisely the opposite of what unmanaged drift tends to produce.
Two Practical Approaches, Compared
Calendar-based rebalancing — review your actual allocation once a year, on a fixed, easy-to-remember date such as your birthday or a specific portfolio-anniversary date, and rebalance back to your original target if it's drifted meaningfully from that target. This approach is simple, genuinely low-effort, and sufficient for the large majority of long-term individual investors who don't want portfolio management to become a frequent, time-consuming task.
Threshold-based rebalancing — rebalance whenever any asset class drifts beyond a predetermined band around its target, commonly something like ±5 percentage points. This approach responds meaningfully faster to genuinely large, sudden market moves than a fixed annual schedule would, but it requires checking your allocation more frequently to actually notice when a threshold has been crossed, which is more ongoing effort than most casual investors are willing to sustain consistently over many years.
For most individual investors without a specific reason to prefer otherwise, calendar-based rebalancing once a year strikes a sensible, sustainable balance between staying genuinely on track with your intended risk level and not over-trading — over-trading itself carries real costs, both in transaction friction and, in taxable accounts, in triggering capital gains tax on every single rebalancing transaction, which threshold-based rebalancing can generate more frequently than most investors realise until they actually see the tax bill.
The Behavioural Benefit That's Easy to Overlook
Rebalancing forces a genuinely mechanical, emotion-free version of "sell high, buy low" into your investing process — trimming back the asset class that's grown into an outsized share of the portfolio (because it performed well) and topping up the one that's lagged (because it performed comparatively poorly), which is precisely the opposite of what raw instinct typically tells most investors to do after watching one asset class outperform strongly for a while. That behavioural discipline, arguably even more than the precise mathematical timing of when exactly you rebalance, is the real, durable value that a consistent rebalancing habit provides over a full investing lifetime.
A Worked Illustration
Starting at ₹10 lakh with a 70/30 split (₹7 lakh equity, ₹3 lakh debt), suppose equity grows 25% over a year while debt grows a modest 7%. Equity is now worth ₹8.75 lakh, debt ₹3.21 lakh, total ₹11.96 lakh — a 73/27 split, drifted from the original 70/30 target. Rebalancing means selling roughly ₹35,000 worth of equity and moving it into debt, restoring the 70/30 split and, mechanically, locking in some of that equity gain rather than leaving the entire windfall exposed to a potential subsequent correction.
When Rebalancing Isn't Actually the Right Move
Rebalancing makes the most sense for a portfolio built around a specific, deliberately chosen long-term target allocation. If your allocation has genuinely, intentionally shifted because your actual goals, time horizon, or risk tolerance have changed — not because of passive market drift — the right move is to consciously set a new target first, rather than mechanically rebalancing back to an old target that may no longer actually reflect what you need from the portfolio going forward.
Frequently Asked Questions
Does rebalancing apply within an asset class too, or only between equity and debt? It can apply within a class as well — for instance, rebalancing between large-cap and small-cap equity funds if one has grown to dominate your equity allocation disproportionately — though most individual investors focus primarily on the broader equity-versus-debt split as the higher-impact rebalancing decision.
Are there tax-efficient ways to rebalance without triggering a large capital gains bill? Yes — directing new investment contributions preferentially toward whichever asset class is currently underweight, rather than selling the overweight asset class outright, achieves a similar rebalancing effect gradually over time without triggering any capital gains tax at all, and is often the more tax-efficient approach for investors who are still actively contributing new money regularly.
Should retirement-specific portfolios rebalance differently from a general long-term goal? Often yes — many investors deliberately shift their target allocation gradually more conservative as a specific goal (like retirement) approaches, meaning the rebalancing exercise each year isn't just restoring an old fixed target but rebalancing toward a new, slightly more conservative target reflecting the shorter remaining time horizon, a distinct concept from simple drift-correction rebalancing toward an unchanged target.