Rebalancing is the process of realigning your investment portfolio back to its original target mix of assets. Over time, as some investments grow faster than others, your portfolio naturally drifts away from the balance you originally set. Rebalancing corrects that drift, and its primary purpose is to manage risk, not to maximize returns.
Why Portfolios Drift
Suppose you set up a portfolio with 70% stocks and 30% bonds. After a strong year in the stock market, your stocks might grow to represent 80% of your portfolio while bonds shrink to 20%. You haven’t changed anything, but your portfolio is now taking on more risk than you intended. That gap between where your portfolio is and where you want it to be is called portfolio drift.
Drift happens constantly because different asset classes earn different returns over any given period. Left unchecked, drift can quietly transform a moderate portfolio into an aggressive one, or vice versa. A portfolio that started balanced before a long bull market could end up heavily concentrated in stocks, leaving you far more exposed to a downturn than you planned for.
How Rebalancing Works in Practice
The mechanics are straightforward. You compare your current allocation to your target, then move money from the asset classes that have grown beyond their target weight into the ones that have fallen below it. In the example above, you would trim some of your stock holdings and use the proceeds to buy more bonds until you’re back at 70/30.
This feels counterintuitive because you’re selling winners and buying underperformers. But that’s exactly the point. You’re systematically taking profits from what’s run up and buying what’s relatively cheap, which keeps your risk level where you set it.
There are a few ways to execute a rebalance without selling anything. If you’re still contributing to the account, you can direct new money entirely into the underweight asset class until the balance corrects itself. You can also redirect dividends and interest payments the same way. Both approaches let you rebalance without triggering any sales, which matters in taxable accounts where selling creates a tax event.
Calendar vs. Threshold Strategies
There are two main approaches to deciding when to rebalance, and neither has historically outperformed the other. The most important thing is picking a rule and sticking with it.
Calendar rebalancing means checking your portfolio at set intervals and adjusting back to target. Most experts suggest doing this quarterly or annually. Checking weekly would generate excessive transaction costs and potential taxable gains, while waiting longer than a year leaves too much room for drift to compound.
Threshold rebalancing (sometimes called tolerance band or corridor rebalancing) ignores the calendar and instead triggers a rebalance whenever an asset class drifts beyond a preset range. For example, you might set a rule that if any asset class moves more than 5 percentage points from its target, you rebalance. This approach requires more monitoring but responds to market moves in real time rather than on an arbitrary schedule.
You can also combine both: check quarterly, but only rebalance if drift has crossed your threshold. This avoids unnecessary trades during calm markets while still catching major shifts.
Tax Implications of Rebalancing
Where you rebalance matters as much as how you do it. In tax-advantaged accounts like IRAs and 401(k)s, buying and selling to rebalance has no immediate tax consequences. Traditional IRAs and 401(k)s let your money grow tax-deferred until you take distributions in retirement, and Roth accounts let you withdraw tax-free if you follow the rules. Rebalance freely inside these accounts.
Taxable brokerage accounts are different. Selling an investment that has gained value triggers capital gains tax. Short-term gains (on assets held less than a year) are taxed at your ordinary income rate, while long-term gains get lower rates. This is why directing new contributions and dividends toward underweight asset classes is especially valuable in taxable accounts. You get the rebalancing effect without generating a tax bill from selling appreciated holdings.
If you hold investments in both taxable and tax-advantaged accounts, consider doing most of your rebalancing inside the tax-advantaged accounts first. You’ll get the same portfolio-level result with fewer tax consequences.
Automated Rebalancing Options
If monitoring and manually adjusting your portfolio sounds like more work than you want, automated tools can handle it. Most robo-advisors automatically rebalance your portfolio so you don’t have to think about it. Vanguard’s Digital Advisor, for example, rebalances whenever it detects your portfolio has drifted more than 5% from the recommended allocation.
Target-date funds offer another hands-off approach. These funds hold a mix of stocks and bonds and rebalance internally on an ongoing basis. They also gradually shift toward more conservative allocations as you approach retirement. You own a single fund and the rebalancing happens inside it.
Many 401(k) plans also offer an automatic rebalancing feature you can enable in your account settings. It typically lets you choose a frequency (quarterly, semiannually, or annually) and handles the trades for you within the plan.
How Often You Really Need to Rebalance
There’s no perfect frequency, and overthinking it does more harm than good. Annual or semiannual rebalancing is sufficient for most people. The goal isn’t precision; it’s preventing your portfolio from quietly becoming something you didn’t sign up for.
Major life changes, like getting closer to retirement, receiving a large inheritance, or shifting your risk tolerance, are also natural moments to revisit your target allocation itself, not just rebalance back to the old one. Rebalancing assumes your target is still right. If your circumstances have changed, update the target first, then rebalance to the new mix.