When you set up an investment portfolio, you choose a mix of assets — stocks, bonds, cash — that fits your goals and risk tolerance. But markets don’t hold still. Over time, strong performers grow to a larger share of your portfolio and weaker ones shrink. Rebalancing is the process of bringing your portfolio back to the mix you intended.
Why Portfolios Drift
Suppose you start with a target allocation of 70% stocks and 30% bonds. If stocks have a strong year and gain 25% while bonds gain 5%, your portfolio might shift to 75% stocks and 25% bonds — even though you never made a deliberate decision to take on more risk.
This drift matters because your asset allocation is how you control risk. A portfolio that’s drifted heavily into stocks is more exposed to market drops than you originally intended. Rebalancing restores your intended risk profile.
How Rebalancing Works
There are two main approaches:
- Sell high, buy low: Sell some of the investments that have grown (trimming what has become overweight) and use the proceeds to buy more of what has underperformed (bringing underweight positions back up). This naturally enforces a buy-low, sell-high discipline.
- Direct new contributions: Instead of selling, direct new contributions toward the underweight positions. This avoids triggering taxable events in a brokerage account and is often the best approach if you’re still adding money regularly.
In practice, most investors use a combination — directing new money first, then selling if the drift is too large to correct that way.
When to Rebalance
There are two common trigger approaches:
- Calendar-based: Rebalance on a set schedule — once a year or once every six months. Simple and predictable.
- Threshold-based: Rebalance when any asset class drifts more than a set percentage from its target (5% is a common threshold). More responsive but requires monitoring.
For most individual investors, annual rebalancing is sufficient. Markets have to move significantly for drift to meaningfully change your risk profile, and rebalancing too frequently in a taxable account can generate unnecessary tax events.
Rebalancing in Tax-Advantaged vs. Taxable Accounts
Rebalancing is simpler and less costly in retirement accounts:
- 401(k) and IRAs: Selling and buying within these accounts doesn’t trigger taxes. You can rebalance freely without worrying about capital gains.
- Taxable brokerage accounts: Selling a position that has gained triggers capital gains tax. Prioritize rebalancing here by directing new contributions rather than selling when possible. If you must sell, long-term gains (held over a year) are taxed at lower rates.
A common strategy: hold bonds and other income-producing assets in tax-advantaged accounts (to shelter interest income), and hold equities in taxable accounts (to take advantage of lower long-term capital gains rates).
How Much Does Drift Matter?
Research suggests that for long-term investors, the frequency and precision of rebalancing matters less than simply having a target and sticking to it. The benefit of rebalancing isn’t primarily about maximizing returns — it’s about managing risk. A portfolio that never gets rebalanced can end up with a dramatically different risk profile than intended, especially after a long bull market in stocks.
Rebalancing as You Approach Retirement
Rebalancing becomes especially important in the years leading up to and through retirement. As your time horizon shortens, the ability to recover from a major market drop shrinks. A portfolio that has drifted to 80% stocks when you’re 63 is a very different risk than it was at 45.
Many financial advisors recommend a more deliberate shift toward bonds and lower-volatility assets — not just rebalancing to a fixed target, but gradually moving the target itself to be more conservative as retirement approaches. Target-date funds do this automatically.
A Simple Approach for Most Investors
If you’re using a target-date fund in your 401(k), rebalancing is handled automatically — you don’t need to do anything. If you manage your own portfolio across multiple accounts, a once-a-year review (perhaps at the same time you do your taxes) is usually enough: check whether your allocation has drifted by more than 5–10 percentage points, and correct by directing new contributions or, if necessary, selling overweight positions.
