What is portfolio rebalancing, and how often should you do it?

Rebalancing returns a portfolio to its intended allocation after market movement pushes it out of shape. If you target 70 percent stocks and 30 percent bonds and a strong year takes stocks to 80 percent, your portfolio now carries more risk than you chose, because the winning asset grew into a larger share. Rebalancing sells some of the winner and buys the laggard to restore the target. Its primary purpose is risk control rather than return enhancement, which is the point most often misunderstood: it keeps you in the portfolio you decided on rather than the one recent performance built for you.

Two triggers are commonly used and both work. Calendar rebalancing checks on a fixed schedule, typically annually. Threshold or band rebalancing acts only when an allocation drifts beyond a set tolerance, commonly five percentage points. Research generally finds that annual or threshold-based approaches capture nearly all the benefit, while more frequent rebalancing increases transaction costs and taxes without improving outcomes. Monitoring quarterly and acting only when a band is breached is a reasonable compromise.

The tax-efficient way to do it matters more than the schedule. Rebalance inside tax-advantaged accounts first, where selling triggers no tax at all. In taxable accounts, direct new contributions and dividends toward the underweight asset rather than selling the overweight one, which rebalances without realizing gains. Pair any necessary sales with loss harvesting where available. And note that target date funds and balanced funds rebalance automatically, which is a genuine convenience for anyone who will not do it consistently, since the most common rebalancing failure is not doing it at all during a market drop, which is precisely when it requires buying the asset everyone is afraid of and when it does the most good.