A portfolio built with a carefully chosen asset allocation rarely stays that way on its own, since different investments inevitably grow at different rates over time, gradually pulling the actual allocation away from its original intended target. Rebalancing addresses this natural drift directly, and understanding how to do it thoughtfully provides genuine, ongoing value to long-term investors.

Why Portfolio Allocation Naturally Drifts Over Time

If stocks perform particularly well over a period while bonds lag, a portfolio’s actual stock allocation will grow to represent a larger percentage of the total portfolio than originally intended, meaning without any active management, the portfolio’s actual risk profile gradually shifts away from what was originally, deliberately chosen.

What Rebalancing Actually Accomplishes

Effect	Explanation
Maintains intended risk level	Prevents unintended allocation drift from changing overall portfolio risk
Enforces disciplined buying and selling	Systematically sells recent outperformers and buys underperformers
Removes emotional decision-making	Follows a predetermined rule rather than reacting to market sentiment

An often underappreciated benefit of rebalancing is that it systematically enforces a disciplined “sell high, buy low” behavior, since rebalancing requires trimming positions that have grown disproportionately large (often because they’ve performed well) and adding to positions that have shrunk (often because they’ve underperformed), a genuinely counterintuitive discipline many investors struggle to maintain without a systematic process.

Common Rebalancing Approaches

1. Calendar-based rebalancing — reviewing and rebalancing the portfolio on a predetermined schedule, such as annually or quarterly, regardless of how much drift has actually occurred
2. Threshold-based rebalancing — rebalancing whenever a specific asset class drifts beyond a predetermined percentage from its target allocation, regardless of the calendar timing
3. Combined approach — reviewing on a set schedule but only actually rebalancing if drift has exceeded a specific threshold

A Practical, Step-by-Step Rebalancing Process

1. Review your current actual allocation across all your investment accounts and holdings combined
2. Compare this current allocation against your target allocation, identifying specific areas of meaningful drift
3. Determine the specific trades needed to bring your allocation back toward your target
4. Execute the rebalancing trades, considering tax implications, particularly in taxable accounts
5. Document the rebalancing and set a reminder for your next scheduled review

Rebalancing Through New Contributions

Rather than always requiring selling overweighted positions, investors regularly adding new contributions to their portfolio can sometimes rebalance simply by directing new investments toward currently underweighted asset classes, potentially achieving the rebalancing goal without needing to sell any existing positions at all.

Tax Considerations When Rebalancing

Rebalancing within a tax-advantaged retirement account generally doesn’t trigger any immediate tax consequences, while rebalancing within a taxable brokerage account can trigger capital gains taxes on any sold positions with unrealized gains, making it worth considering rebalancing through new contributions where possible, or being strategic about which specific tax lots to sell when rebalancing in a taxable account.

How Often Should You Actually Rebalance

There’s no single universally correct rebalancing frequency, though many financial professionals suggest reviewing at least annually, or using a threshold-based approach triggering rebalancing when an asset class drifts beyond a specific percentage, such as five percentage points, from its target allocation, balancing the benefits of maintaining discipline against the practical costs and effort of overly frequent trading.

Rebalancing Across Multiple Accounts

For investors with multiple accounts — a 401(k), an IRA, and a taxable brokerage account, for example — considering your overall combined asset allocation across all accounts together, rather than treating each account’s allocation in complete isolation, often provides more flexibility, particularly around directing rebalancing trades toward accounts where they won’t trigger unwanted tax consequences.

Avoiding Common Rebalancing Mistakes

• Rebalancing too frequently, incurring unnecessary transaction costs or tax consequences for relatively minor allocation drift
• Never rebalancing at all, allowing significant allocation drift that meaningfully changes the portfolio’s actual risk profile over time
• Letting emotions override the systematic process, such as hesitating to sell a recently strong-performing asset class even when your predetermined rebalancing rule calls for trimming it

Frequently Asked Questions

Does rebalancing guarantee better investment returns?

Not necessarily in every specific period, though rebalancing’s primary purpose is maintaining your intended risk level and enforcing disciplined behavior, rather than guaranteeing outperformance; the genuine value lies more in risk management and behavioral discipline than in a reliable return enhancement.

How much drift from my target allocation should trigger a rebalance?

Many investors use a threshold somewhere in the range of five percentage points of drift from a specific target allocation as a reasonable trigger point, though this specific threshold can reasonably vary based on individual preference and the practical costs involved in rebalancing.

Can I automate portfolio rebalancing?

Yes — many robo-advisors and some brokerage platforms offer automatic rebalancing features, systematically maintaining your target allocation without requiring manual intervention, which can be a genuinely convenient option for investors who prefer a more hands-off approach.

Should I rebalance during a significant market downturn?

Maintaining your rebalancing discipline through market downturns, rather than abandoning it out of anxiety, is actually part of the strategy’s core value, since a downturn often creates exactly the kind of allocation drift (with equities falling relative to more stable holdings) that a rebalancing approach is specifically designed to address.

Final Thoughts

Portfolio rebalancing addresses the natural, inevitable drift that occurs as different investments perform differently over time, providing genuine value both through maintaining your intended risk level and enforcing a disciplined, systematic buying and selling process. Establishing a clear rebalancing approach, whether calendar-based, threshold-based, or a combination, and maintaining that discipline consistently, including through periods of market volatility, provides meaningful, ongoing value to long-term portfolio management.