A portfolio left completely alone does not stay balanced. It drifts, quietly and steadily, toward whatever happened to perform best, until the risk it carries looks nothing like the plan it started with.
Rebalancing brings a portfolio back to its original target allocation after market movement has shifted the actual weighting away from the plan. This usually means selling a portion of whatever has grown to be overweight and buying more of whatever has fallen behind, a process that runs directly against the instinct to keep holding what has been performing well. The discipline behind rebalancing exists specifically to manage risk, not to chase the highest possible return.
Inside a tax advantaged account like a 401k or an IRA, rebalancing carries no tax consequence at all, since trades inside these accounts do not trigger capital gains taxes regardless of how often they happen. The complication arrives specifically in taxable brokerage accounts, where selling an appreciated asset to rebalance creates a taxable event that needs to be managed carefully.
Using New Contributions Instead of Selling
The simplest way to rebalance a taxable account without triggering any tax consequence at all is to direct new contributions toward whichever asset class has fallen below its target weighting, rather than selling anything from the overweight position. This approach works best for portfolios still actively receiving regular contributions, since it can gradually correct an imbalance over several months without a single taxable sale.
Dividend and interest payments generated within the account can be redirected the same way, reinvested specifically into the underweight asset class rather than automatically reinvested into whatever generated the payment in the first place. Most brokerages allow this kind of manual redirection, though it requires turning off automatic dividend reinvestment on individual holdings and directing the cash manually instead.
This gradual approach takes longer than an immediate sell and rebuy rebalance, and it works less well for a portfolio that has drifted significantly from its target, where new contributions alone would take years to correct the imbalance. For smaller drifts, though, it remains the cleanest way to avoid an unnecessary tax bill entirely.
Managing Taxes When Selling Is Unavoidable
Selling specific tax lots strategically, rather than letting a brokerage default to a first in first out method, can reduce the tax impact of a necessary rebalance considerably. Choosing to sell shares with a higher cost basis first, when the brokerage platform allows lot selection, minimizes the taxable gain compared to selling the oldest, most appreciated shares by default.
Pairing a rebalancing sale with tax loss harvesting elsewhere in the portfolio, selling a different holding that has lost value to offset the gain from the rebalancing trade, can neutralize much of the tax impact in the same calendar year. This strategy requires some coordination and works best with the guidance of a tax professional familiar with the full picture of a household’s investment accounts.
Timing a taxable rebalance for a year with unusually low income, such as a year with a career gap or reduced earnings, can also reduce the tax rate applied to any resulting capital gains, since long term capital gains rates are tied directly to overall taxable income for the year.
Letting Some Funds Rebalance Automatically
Target date funds and certain balanced funds rebalance internally on a regular schedule without requiring any action from the investor, and without generating a taxable event for the investor personally, since the fund itself absorbs the trading activity inside its own structure. This built in rebalancing is one of the more underappreciated aspects of how target-date funds effectively manage a portfolio without the investor needing to think about drift at all.
Holding a portion of a portfolio in one of these automatically rebalancing funds, alongside individually selected holdings that require manual rebalancing, offers a middle ground for investors who want some hands off structure without giving up full control over the rest of the portfolio.
Reviewing an entire portfolio’s allocation once or twice a year, rather than constantly, strikes a reasonable balance between staying disciplined about risk and avoiding the transaction costs and tax consequences that come with rebalancing too frequently.
Robo-advisors and managed brokerage accounts often handle this entire rebalancing process automatically behind the scenes, including tax-aware rebalancing logic that manually managing an account would take real effort to replicate. For investors who would rather not think about lot selection and tax timing at all, shifting a taxable account into one of these managed services removes much of the complexity described here.
