Rebalancing is the process of buying or selling holdings to bring a portfolio back to its original target mix of asset categories, such as stocks, bonds, and cash, after market movements have shifted those proportions away from plan.
What Does Rebalancing a Portfolio Mean?
Rebalancing means restoring a portfolio to a previously chosen asset allocation — the division of a portfolio among asset categories such as stocks, bonds, and cash. According to the U.S. Securities and Exchange Commission's investor-education guide on asset allocation, an investor first sets a target mix based on time horizon and risk tolerance, then periodically checks whether actual holdings still match that mix.
The same SEC guide describes rebalancing as "bringing your portfolio back to your original asset allocation mix" and recommends investors do it "at least once a year," typically every six to twelve months, to prevent any single asset category from becoming an outsized share of the total. The guide frames this as one tool among several for managing risk, not a guarantee against loss.
Rebalancing is distinct from diversification, which is the practice of spreading money across different investments to reduce concentration in any one holding. A portfolio can be diversified and still drift out of balance over time as its components grow at different rates.
Why Does an Allocation Drift From Its Target?
An allocation drifts because asset classes grow at different rates. A portfolio set at 60% stocks and 40% bonds will hold a larger stock share after a period in which stocks outperform bonds, and a smaller one after stocks underperform. Left unchecked, the drift compounds each period.
Investor.gov, the SEC's investor-education site, explains diversification with the shorthand "don't put all your eggs in one basket": spreading money across assets with different risk and return characteristics can offset losses in one holding with gains in another. The site notes this reduces the severity of losses in a downturn but does not prevent them — a distinction rebalancing does not change.
Over multiple years without intervention, drift can leave a portfolio meaningfully more concentrated in higher-volatility assets than the investor originally chose, changing the portfolio's risk profile without any deliberate decision to take on more risk.
How Is Rebalancing Different From Diversification and Allocation?
Diversification, allocation, and rebalancing are three related but distinct steps, and conflating them is a common source of confusion. Allocation is the initial decision about how to divide money among categories. Diversification is the practice of spreading holdings within and across those categories to avoid concentration in any single investment.
Rebalancing is the maintenance step that comes after both: it does not change the target allocation or the diversification strategy, only the actual weights of what is already held, so that they continue to match the plan set at the outset. A portfolio can be well diversified — holding many individual securities — and still be out of balance if one category has grown to dominate the total.
Investor.gov frames diversification as a way to offset losses in one holding with gains in another rather than eliminate the possibility of loss altogether. Rebalancing does not add this protection on its own; it only restores the mix the investor originally chose for a given level of risk tolerance and time horizon.
What Are the Two Main Rebalancing Methods?
Investors generally choose between two mechanical approaches, each with documented trade-offs. Neither is universally superior; the choice depends on an individual's time, transaction costs, and account type.
| Method | How It Works | Documented Trade-Off |
|---|---|---|
| Calendar rebalancing | Portfolio is checked and adjusted on a fixed schedule, such as annually or semiannually. | Simple and predictable, but may rebalance too often or too rarely relative to actual market movement. |
| Threshold (percentage-of-portfolio) rebalancing | Portfolio is adjusted only when an asset class drifts beyond a set percentage from its target. | Responds to actual drift rather than the calendar, but requires more frequent monitoring. |
The SEC's asset-allocation guide recommends a calendar-based check of "every six to twelve months" as a general practice, without specifying a single correct interval for all investors, and ties the choice back to the investor's own time horizon and risk tolerance.
How Does Rebalancing Interact With Taxes?
Selling appreciated holdings to rebalance a taxable account can trigger capital gains taxes, while the same trade inside a tax-advantaged account such as an IRA or 401(k) typically does not create an immediate tax event. This is a structural feature of account type, not a feature of rebalancing itself.
Because of this, investors and their tax advisers often use new contributions or dividend reinvestment to nudge a taxable account back toward target before selling existing positions, reducing the portion of the rebalance that requires a taxable sale. Actual tax consequences depend on an individual's holding period, tax bracket, and account structure.
This article does not address any individual's tax position; a licensed tax professional is the appropriate source for that analysis.
What Are the Documented Trade-Offs of Rebalancing?
Rebalancing enforces a "sell high, buy low" discipline by trimming the asset class that has grown and adding to the one that has lagged, which can counter the emotional pull to chase recent performance. Educational material from The Motley Fool illustrates the related principle with a comparison of long-run average annual returns across allocations weighted toward bonds versus stocks, showing that allocations with a larger bond share have historically shown lower volatility alongside lower average returns over the periods studied.
The trade-off is direct: an allocation left to drift toward its best-performing asset class can produce higher returns in a continuing bull market for that asset class, while periodic rebalancing gives up some of that upside in exchange for keeping the portfolio's risk level closer to what the investor originally chose. Neither outcome is guaranteed, and past performance figures describe only the periods measured.
Transaction costs and, in taxable accounts, capital gains taxes are the direct costs of rebalancing and are weighed against the benefit of risk control on a case-by-case basis.
What This Means for an Individual Portfolio
This article is educational information, not investment advice. Whether to rebalance, how often, and by which method depends on an individual's time horizon, risk tolerance, tax situation, and account structure — circumstances this article cannot know. No allocation or rebalancing frequency is recommended here.
For a related business news perspective, read How Portfolio Rebalancing Works and When Investors Use It.
