Even a carefully built portfolio drifts from its original allocation over time simply because different asset classes grow at different rates. A portfolio that started at 70% stocks and 30% bonds can quietly become 80% stocks after a strong bull run, quietly taking on more risk than you originally signed up for. Rebalancing is the maintenance step that brings your portfolio back in line.

Here’s how rebalancing actually works, the methods available, and how to do it without triggering an unnecessary tax bill.

Why Portfolios Drift Without Any Action From You

Stocks and bonds don’t grow at the same pace, especially over shorter stretches. A multi-year stock rally can leave your portfolio far more stock-heavy than intended, while a prolonged downturn can do the opposite. Neither situation is inherently wrong, but both mean your actual risk exposure no longer matches the level you chose deliberately.

Rebalancing simply means selling a portion of what’s grown to be overweight and buying more of what’s become underweight, restoring your target percentages.

Calendar-Based Rebalancing

Calendar-based rebalancing means checking and adjusting your portfolio on a fixed schedule, regardless of how far it has drifted. Common intervals include:

• Quarterly
• Semi-annually
• Annually

Annual rebalancing is the most common choice for long-term investors, since it’s frequent enough to control risk drift while minimizing transaction activity and tax events. Checking too often can lead to unnecessary trading and higher costs without meaningfully improving results.

Threshold-Based Rebalancing

Threshold-based rebalancing, sometimes called percentage-of-portfolio rebalancing, triggers a rebalance only when an asset class drifts beyond a predetermined band, such as five percentage points from its target. Under this method, you might check your portfolio monthly but only actually trade when a threshold is breached.

Method	Trigger	Pros	Cons
Calendar-based	Fixed date (e.g., annually)	Simple, predictable, low effort	May rebalance when unnecessary, or miss significant drift between dates
Threshold-based	Allocation drifts past a set band	Responds to actual risk drift	Requires more frequent monitoring
Hybrid	Check on a schedule, trade only if threshold breached	Balances simplicity and responsiveness	Slightly more complex to set up

A hybrid approach, checking your allocation on a set schedule but only trading when drift exceeds a chosen threshold, captures much of the benefit of both methods without the downsides of either extreme.

How to Actually Rebalance a Portfolio

The mechanics are straightforward once you’ve decided on a method:

1. Calculate your current allocation across all accounts, not just one
2. Compare it against your target allocation
3. Identify which asset classes are overweight and which are underweight
4. Sell a portion of the overweight assets and use the proceeds to buy the underweight ones
5. Where possible, direct new contributions toward underweight assets first, reducing the need to sell anything at all

That last step, using new contributions to rebalance rather than selling existing holdings, is often the most efficient approach because it avoids transaction costs and potential tax consequences entirely.

Rebalancing Across Multiple Accounts

Most investors hold money across several accounts, such as a 401(k), an IRA, and a taxable brokerage account. Rather than rebalancing each account individually to match the same target allocation, treat all accounts together as one combined portfolio. This lets you place tax-inefficient assets like bonds in tax-advantaged accounts and place tax-efficient assets like broad stock index funds in taxable accounts, while still hitting your overall target mix.

Tax Considerations When Rebalancing

Rebalancing inside tax-advantaged accounts like 401(k)s and IRAs triggers no immediate tax consequences, since gains and losses inside these accounts aren’t taxed until withdrawal. Rebalancing inside a taxable brokerage account is a different story, since selling appreciated positions can trigger capital gains taxes.

A few ways to reduce the tax impact of rebalancing in taxable accounts:

• Prioritize rebalancing within tax-advantaged accounts first, before touching taxable holdings
• Use new contributions to buy underweight assets instead of selling overweight ones
• Where you must sell, consider harvesting losses elsewhere in the same tax year to offset gains
• Be mindful of the difference between short-term and long-term capital gains rates, since selling a position held less than a year typically triggers a higher tax rate

Frequently Asked Questions

How often should I rebalance my portfolio?

Once or twice a year works well for most long-term investors, either on a fixed calendar schedule or when an asset class drifts beyond a set threshold, such as five percentage points from target.

Does rebalancing guarantee better returns?

No. Rebalancing is a risk-management tool, not a return-boosting strategy. Its purpose is keeping your portfolio’s risk level consistent with your original plan, not maximizing returns.

Can I avoid taxes when rebalancing a taxable account?

You can reduce the tax impact by using new contributions to buy underweight assets and by rebalancing tax-advantaged accounts first, but selling appreciated positions in a taxable account will generally trigger some tax if a sale is necessary.

What if I never rebalance at all?

Your portfolio will drift toward whatever asset class performs best over time, which usually means taking on more risk than originally intended. Over a full market cycle, this can leave you overexposed right before a downturn.

Final Thoughts

Rebalancing is a simple discipline that keeps your portfolio’s risk aligned with the plan you set out to follow, rather than whatever the market happens to have done recently. Pick a method, whether calendar-based, threshold-based, or a hybrid of the two, use new contributions to do as much of the work as possible, and be deliberate about tax consequences in taxable accounts. Consistency matters far more here than precision.