Rebalancing is the practice of periodically restoring your portfolio to its target mix of stocks, bonds, and other assets. Left alone, a portfolio drifts as winners grow and losers shrink, quietly changing your risk level. This guide explains why rebalancing matters and how to do it without overthinking.
Why portfolios drift
Suppose you set a target of 70% stocks and 30% bonds. After a strong stock rally, stocks might swell to 80% of your portfolio, leaving you with more risk than you intended. The opposite happens after a crash, when stocks shrink and you become unintentionally conservative. Rebalancing corrects this drift so your risk stays aligned with your plan.
The disciplined buy-low, sell-high
Rebalancing forces a counterintuitive but healthy habit, because you trim the assets that have risen and add to those that have lagged. In effect you sell high and buy low on a schedule, without needing to predict anything. This removes emotion from the decision and imposes discipline when instinct says to chase winners. Over time it can slightly improve returns and, more importantly, control risk.
Time-based and threshold methods
Two common approaches trigger a rebalance. The calendar method reviews the portfolio on a fixed schedule, such as once a year. The threshold method rebalances only when an asset drifts more than a set amount from its target, often five percentage points. Some investors combine both, checking annually but acting only if drift is large, and either way it helps to avoid tinkering too often, which raises costs and taxes.
Minimizing taxes and costs
In tax-advantaged accounts like IRAs and 401(k)s, you can rebalance freely because sales trigger no immediate tax. In taxable accounts, selling appreciated assets can create capital gains, so it is often smarter to rebalance by directing new contributions and dividends toward the underweight assets. This adds to laggards without selling winners. Rebalancing a few times a year at most keeps costs low.
You target 70% stocks and 30% bonds, but a bull market pushes stocks to 80%. Rebalancing means selling enough stock to bring it back to 70% and buying bonds with the proceeds, or steering new contributions into bonds until the mix is restored.
Key takeaways
- Rebalancing restores your portfolio to its target asset mix.
- Drift from market moves quietly changes your risk level over time.
- It enforces a disciplined sell-high, buy-low habit without forecasting.
- Use a calendar schedule, a drift threshold, or both to decide when to act.
- Rebalance in tax-advantaged accounts or with new cash to limit taxes.
Common mistakes
- Rebalancing so often that trading costs and taxes eat the benefit.
- Selling appreciated funds in a taxable account when new contributions could fix the drift.
- Letting a winning asset run unchecked until your risk is far above your comfort level.
FAQ
How often should I rebalance?
Once a year, or whenever an asset drifts more than about five percentage points from its target, is plenty for most investors.
Does rebalancing boost returns?
Its main job is controlling risk. It can modestly help returns by trimming winners and adding to laggards, but that is a secondary benefit.