Rebalancing is one of the most straightforward and consistently recommended practices in long-term investing — and one of the most commonly ignored. It is the process of periodically adjusting your portfolio back to its target allocation after market movements have caused it to drift. Done correctly, rebalancing is a low-effort, once-per-year activity that improves risk management and can modestly improve long-term returns. Here is what it is, why it matters, and exactly how to do it.
| Target allocation | After bull market | After rebalancing | |
|---|---|---|---|
| US stocks | 60% | 72% | 60% |
| International stocks | 20% | 16% | 20% |
| Bonds | 20% | 12% | 20% |
Why Drift Happens
Different asset classes produce different returns over time, which means a portfolio that starts with a specific allocation will naturally drift from it as the higher-returning components grow relative to the lower-returning ones. After a strong period for US equities, for example, a portfolio that started at 60 percent stocks might be at 70 or 75 percent stocks, with bonds and international stocks reduced proportionally. The portfolio is now taking more equity risk than the investor originally intended — a risk level that may be inappropriate if it was calibrated to the investor’s actual risk tolerance when the allocation was set.
This drift also has the opposite effect after market downturns: a portfolio that falls sharply in equities may end up significantly underweight stocks relative to target — a position that misses the recovery if not corrected. Rebalancing after a downturn means buying equities when they are lower, which is both disciplined and potentially return-enhancing. It converts the instinct to reduce equity exposure after a decline into the opposite action, which is what the evidence supports.
How to Rebalance
Rebalancing is mechanically simple. Check your current allocation across all accounts — most brokerage platforms show the current allocation as a percentage breakdown. Compare to your target allocation. If any asset class is more than 5 to 10 percentage points away from its target, rebalance by selling what has grown above target and buying what has fallen below it, or by directing new contributions toward the underweight asset class rather than buying and selling existing positions.
In tax-advantaged accounts — 401k, Roth IRA — rebalancing through buying and selling has no immediate tax consequences, making it the most straightforward approach. In taxable brokerage accounts, selling appreciated positions to rebalance triggers capital gains taxes, which is a real cost. In taxable accounts, the preferred approach when possible is to rebalance by directing new contributions to the underweight asset class rather than selling existing positions, avoiding the tax consequence while still restoring the target allocation over time.
How Often to Rebalance
The research on optimal rebalancing frequency suggests that annual rebalancing performs as well as or better than more frequent rebalancing for most investors, with less tax cost and less transaction overhead. Quarterly or monthly rebalancing does not produce meaningfully better risk-adjusted returns and generates higher costs in taxable accounts. The two most practical approaches: rebalance on a fixed schedule once per year — same month, same process — or rebalance whenever any asset class drifts more than 5 percentage points from its target. Both approaches work; the annual calendar approach requires no monitoring and is simpler to sustain.
Some target-date funds and robo-advisors rebalance automatically, which removes the task entirely. If you hold a single target-date fund, rebalancing is handled without any action on your part. For investors holding multiple funds across multiple accounts, the annual manual rebalance is a small time investment — typically 15 to 30 minutes — that maintains the risk level you chose when you set the allocation.
The Return Impact of Rebalancing
The evidence on whether rebalancing improves returns is mixed. In some market environments — notably those with mean-reverting patterns where asset classes that underperform eventually outperform — rebalancing produces a “rebalancing bonus” by systematically buying low and selling high. In persistently trending markets, rebalancing may slightly reduce returns by trimming the best-performing asset. Over long periods and across many market environments, the return impact of rebalancing is small in either direction — the primary value is risk management, not return enhancement.
The more important benefit is psychological: a portfolio that drifts significantly above its equity target will fall more sharply in a market downturn than the investor originally planned for, which increases the probability of panic selling at the wrong time. Keeping the portfolio near its target allocation keeps the volatility within the range the investor consciously calibrated to their risk tolerance — which is the foundation for staying invested through downturns rather than selling at lows.
Rebalancing Across Multiple Accounts
Investors with multiple accounts — a 401k, a Roth IRA, a taxable brokerage — can optimise rebalancing by treating the portfolio as a whole rather than rebalancing each account independently. The target allocation applies to the total portfolio across all accounts, not to each account individually. This means you can hold all your bonds in the 401k and all your equities in the Roth IRA if that is tax-efficient, and still maintain your overall target allocation when the totals are combined. Rebalancing can then happen through new contributions to underweight accounts rather than selling in any account — the most tax-efficient approach for taxable investors with multiple accounts to work with.
When to Rebalance More Aggressively
There are specific circumstances where more active rebalancing is appropriate beyond the standard annual review. Large one-time market events — a crash of 30 percent or more, or an extended bull run that has dramatically tilted the portfolio above its equity target — are worth addressing even if the annual review date is months away. The threshold most financial planners suggest: rebalance when any asset class is more than 5 percentage points above or below its target, regardless of calendar timing. This threshold-based approach combines the simplicity of a rule with the responsiveness to genuinely significant drift that calendar-only rebalancing misses during unusually volatile periods. For most investors in most years, the annual review is sufficient. In years with significant market movements, the threshold provides a safety valve that keeps the portfolio’s risk profile from straying too far from the investor’s intentions.
Rebalancing is a small but important piece of good investment practice. Like most small important practices, its value is not in any single application but in the cumulative effect of doing it consistently over decades — maintaining the risk level you set deliberately, buying into asset classes when they are relatively cheap, and never allowing success in one part of the portfolio to silently increase the risk of the whole. Set up the system, do the annual review, and let the portfolio run as designed.
The simplest rebalancing system that requires the least ongoing attention: once per year, open your investment accounts, look at the current allocation, and if any component is more than 5 to 10 percentage points away from its target, redirect new contributions to the underweight component until the allocation is restored. In most years this is all the rebalancing required. In years with extreme market movements, also review whether the threshold has been crossed between annual reviews. Set a calendar reminder for the same date each year, follow the process, and otherwise leave the portfolio alone. The discipline is not in the sophistication of the rebalancing strategy. It is in doing it consistently, without being tempted to overlay market views or timing judgements on a mechanical process that works precisely because it removes those judgements from the equation.
Most investors who understand rebalancing and commit to doing it annually also discover something useful about their own risk tolerance in the process. The first time you rebalance after a strong equity run — selling some stocks that have done well to buy bonds that have lagged — the discomfort of selling winners is real and informative. The first time you rebalance after a market decline — buying equities that have fallen to restore your target — is also uncomfortable in a different way. Both discomforts are worth experiencing because they reveal how your actual reaction to portfolio movements compares to your stated risk tolerance when the allocation was set. That self-knowledge is genuinely valuable and is part of what rebalancing disciplines you toward over time.
Annual rebalancing takes about 20 to 30 minutes for most portfolios. Over a 35-year investing career, that is roughly 12 hours of total work that maintains the risk structure of the portfolio and provides the discipline of systematically buying low and selling high at a portfolio level. Few investments of time in personal finance produce a better return per hour than this one.
