How to Rebalance a Portfolio (And How Often to Do It)

If you are wondering how to rebalance a portfolio—and how often you actually need to do it—the most direct answer is this: you rebalance by selling a portion of the assets that have grown beyond your target allocation and using those proceeds to buy more of the assets that have fallen behind. For most long-term investors, the most effective approach is to check your portfolio on a set schedule (such as once or twice a year) and only make trades if an asset class has drifted by 5% or more from its intended target.

While the mechanics are straightforward, the discipline of portfolio rebalancing is often misunderstood. It is not a tool designed to maximize your returns. Rather, it is a risk-management strategy. By systematically trimming your winners and buying your underperformers, you force yourself to buy low and sell high, ensuring your portfolio's risk level remains aligned with your long-term goals.

Let us explore why portfolios drift, the different strategies for deciding when to act, and how to realign your assets without generating unnecessary tax bills.

Understanding asset allocation drift

To grasp why rebalancing is necessary, you first need to understand asset allocation drift. When you initially build a portfolio, you choose a target asset allocation based on your time horizon and risk tolerance. For instance, you might decide on a moderate allocation of 60% stocks and 40% bonds.

Over time, financial markets move at different speeds. Stocks generally offer higher long-term growth potential but come with higher volatility, while bonds tend to offer lower, steadier returns. In a strong bull market, your stock holdings might grow significantly while your bonds grow modestly or even decline.

After a few years of strong stock performance, your original 60/40 portfolio might have quietly shifted into a 75/25 portfolio. This is asset allocation drift. You haven't done anything wrong—in fact, your investments have grown—but your portfolio is now carrying significantly more equity risk than you originally intended. If a severe market downturn were to occur, a 75% equity allocation would suffer much steeper losses than a 60% equity allocation.

Portfolio rebalancing pulls your investments back to their anchor, preventing your risk profile from creeping upward over time.

Deciding when to rebalance

One of the most common questions from investors is exactly when to rebalance. If you check your accounts too often and trade at every minor fluctuation, you will rack up transaction fees and potential taxes. If you wait too long, your portfolio could become dangerously unbalanced.

There are three primary frameworks for deciding when to take action:

Calendar-based rebalancing

In this approach, you ignore the day-to-day noise of the market and rebalance your portfolio on a strict schedule—typically annually, semi-annually, or quarterly. For example, you might decide to realign your portfolio every year during the first week of January. This method is incredibly simple and helps remove emotion from the equation, but it ignores how much the market has actually moved. You might end up trading when your portfolio has barely drifted, or you might leave a wildly drifting portfolio unchecked for months until your calendar date arrives.

Threshold-based rebalancing

Also known as tolerance-band rebalancing, this strategy ignores the calendar entirely. Instead, you establish a maximum allowable deviation—or "threshold"—for each asset class. A common rule of thumb is 5%. If your target for stocks is 60%, you only rebalance if your stock allocation rises above 65% or falls below 55%. This ensures you only trade when a meaningful deviation has occurred. The downside? It requires constant monitoring of your portfolio's daily balances to know when a threshold is breached.

The time-and-threshold strategy

For most retail investors, a hybrid approach offers the best of both worlds. Research from major financial institutions routinely points to this combined method as a highly efficient rebalancing strategy.

With a time-and-threshold strategy, you check your portfolio on a set schedule (say, once a year). However, you only execute a rebalance if an asset class has drifted past your pre-set threshold (like 5%). If you check your portfolio and your 60% stock target has only drifted to 62%, you do nothing and wait until the next calendar check-in. This minimizes unnecessary trading while still tightly controlling risk.

How to calculate your rebalancing needs

Let us walk through a concrete example to see exactly how to rebalance a portfolio using simple math.

Assume you have a $100,000 portfolio. Your target asset allocation is 70% US Stocks and 30% US Bonds.

• Target Stocks: $70,000
• Target Bonds: $30,000

Over the next year, the stock market experiences a major rally, and your stock holdings grow by 25%. Meanwhile, interest rates rise, and your bond holdings decline by 2%.

• Current Stocks: $87,500
• Current Bonds: $29,400
• New Portfolio Total: $116,900

Next, you calculate your current asset allocation percentages by dividing the current value of each asset by the new portfolio total.

• Stock Allocation: $87,500 ÷ $116,900 = 74.85%
• Bond Allocation: $29,400 ÷ $116,900 = 25.15%

Your stock allocation has drifted nearly 5% above your 70% target. If you are using a 5% threshold, it is time to rebalance. To find out exactly how much to buy and sell, calculate what your target dollar amounts should be based on the new total portfolio value.

• Desired Stock Value: 70% of $116,900 = $81,830
• Desired Bond Value: 30% of $116,900 = $35,070

Finally, compare your current holdings to your desired holdings:

• Stocks: You currently have $87,500 but only want $81,830. You need to sell $5,670.
• Bonds: You currently have $29,400 but want $35,070. You need to buy $5,670.

By executing these two trades, you successfully lock in a portion of your stock market gains and buy bonds at a lower relative price, restoring your portfolio to its 70/30 equilibrium.

Smart strategies to rebalance without overtrading

Selling assets to rebalance can sometimes create a hidden drag on your wealth in the form of capital gains taxes and trading fees. Fortunately, there are several tax-efficient ways to implement your rebalancing strategy without indiscriminately hitting the "sell" button.

1. Direct new cash flows

The most tax-efficient way to rebalance is to do so using new money. If you are still in the accumulation phase of your investing journey and making regular contributions to your accounts, simply direct your new deposits toward the asset class that is currently underweight. In the previous example, instead of selling $5,670 in stocks and triggering a taxable event, you could simply direct your next $5,670 in cash savings entirely into bonds.

2. Reinvest dividends strategically

Rather than automatically reinvesting dividends back into the fund that generated them (a feature known as a DRIP), you can have your dividends sweep into a cash settlement fund. You can then use that accumulated cash during your annual review to buy whichever asset class has fallen below its target.

3. Utilize tax-advantaged accounts first

It is important to look at your portfolio holistically across all your accounts. If you hold identical or similar broad-market funds in both a taxable brokerage account and a tax-advantaged account (like a 401(k) or an IRA), do your selling and buying inside the tax-advantaged account.

Because IRAs and 401(k)s shield you from immediate taxation on capital gains, you can freely exchange funds within them without worrying about generating a tax bill. Leave your taxable accounts alone to grow tax-deferred as much as possible.

4. Be mindful of short-term capital gains

If you must sell assets in a taxable account to rebalance, pay close attention to how long you have held those assets. In the United States, investments held for less than a year are subject to short-term capital gains tax rates, which are typically much higher than long-term capital gains rates. If an overweight asset is nearing the one-year mark, it may be financially advantageous to wait a few weeks before selling to secure the more favorable long-term tax treatment.

Maintaining the discipline

Ultimately, a successful rebalancing strategy relies entirely on discipline. It goes against human psychology to sell the assets that have been generating the highest returns and channel that money into the laggards. Yet, this contrarian action is precisely what keeps your portfolio grounded.

By setting a clear target asset allocation, choosing a sensible time-and-threshold strategy, and utilizing tax-efficient methods to move your capital, you can take the emotion out of investing and keep your long-term financial plan firmly on track.