Portfolio rebalancing is the process of periodically realigning your investment portfolio’s asset allocation back to its target — selling assets that have grown above their target percentage and buying those that have fallen below. It sounds simple and somewhat counterintuitive: sell what has been performing well and buy what has been performing poorly. Yet rebalancing is a disciplined practice that manages risk, maintains your intended exposure to different asset classes, and can modestly improve long-term returns by systematically implementing a buy-low, sell-high discipline that most investors struggle to execute emotionally.
Why Portfolios Drift and Why It Matters
If you set an initial portfolio with 70 percent equities and 30 percent bonds, that allocation will not remain at 70/30 indefinitely. When stocks perform well, the equity portion grows to a larger share of the portfolio — perhaps 80 percent after several years of strong equity returns — and the bond portion shrinks proportionally. When stocks have a bad year, the equity share shrinks. These drifts from your target allocation are not neutral: an equity allocation that has drifted to 85 percent means you are taking more risk than you originally intended and are more exposed to a stock market decline than your plan assumed. A drift to 55 percent equities means you have less growth exposure than your plan required and may fall short of return objectives needed to meet goals.
Rebalancing restores the risk level you deliberately chose rather than allowing market performance to dictate your effective risk exposure. This is particularly important in the years approaching or early in retirement, when taking on unintended equity risk through drift can expose a portfolio to sequence-of-returns risk — the damaging possibility of a major market decline just as withdrawals begin. Rebalancing maintains the defensiveness you intended.
When to Rebalance: Calendar vs. Threshold Approaches
There are two primary approaches to determining when rebalancing is needed. Calendar rebalancing sets a regular schedule — annually, semi-annually, or quarterly — and rebalances on that schedule regardless of how much drift has occurred. Annual rebalancing is the most commonly recommended frequency for most investors, providing a systematic check without excessive trading. More frequent rebalancing adds complexity and trading costs without proportional benefit for most portfolios.
Threshold rebalancing triggers a rebalance when any asset class drifts more than a specified percentage from its target — typically 5 percentage points. A 70 percent equity target with a 5 percent threshold would trigger rebalancing if equities reach 75 or fall to 65 percent. This approach rebalances more during volatile markets when drift happens quickly, and less during calm markets. Combining approaches — rebalance annually and also when any threshold is breached — captures the benefits of both. The specific method matters less than having a consistent method and following it through market volatility when the emotional pull is to let winners run further rather than trimming them.
Tax-Efficient Rebalancing Strategies
Rebalancing in tax-advantaged accounts — IRAs and 401(k)s — is straightforward because there are no immediate tax consequences from selling and buying within the account. The primary implementation mechanism for most investors should be rebalancing through their tax-advantaged accounts, as the absence of capital gains taxation makes this both simple and cost-free from a tax perspective. Direct new contributions to underweight asset classes rather than selling overweight ones when possible — this achieves the rebalancing effect without any selling.
In taxable accounts, selling appreciated assets to rebalance creates capital gains that are taxable in the year of the sale. Tax-efficient rebalancing in taxable accounts uses several strategies to minimize this cost. Selling only assets held for more than one year to qualify for the lower long-term capital gains rate rather than ordinary income rates. Using new contributions to purchase underweight assets rather than selling overweight ones. Directing dividends to underweight asset classes. Harvesting losses in underweight assets to offset gains from overweight asset sales — tax-loss harvesting. If equity returns have been very strong, accepting some degree of drift rather than selling highly appreciated assets and paying the capital gains tax may be the better after-tax choice, particularly if the drift is modest. The goal is maintaining reasonable alignment with your target allocation while minimizing the tax cost of achieving it.