Rebalancing: The Unglamorous Habit That Keeps a Portfolio on Plan

Choosing an allocation is the decision everyone remembers. Maintaining it is the work that determines whether the allocation ever mattered.

A portfolio does not stay where you put it. Stocks and bonds grow at different rates, one region or sector pulls ahead, and a large RSU vest or a tender offer can add a lump of one asset overnight. Left alone, a carefully chosen 70/30 mix can quietly become 85/15. Rebalancing is the practice of periodically returning the portfolio to its intended mix. It is not a source of extra return in any reliable sense, but it is one of the few investment decisions fully within an investor's control.

Why drift matters

The SEC's asset allocation guide describes rebalancing as bringing a portfolio back to its original allocation, either by selling what has grown overweight, buying what has fallen underweight, or directing new contributions toward the underweight categories. The point is risk control. Vanguard's research on rebalancing offers a concrete illustration: a portfolio that started at 60% stocks and 40% bonds in 2003 and was never rebalanced would have drifted to roughly 80% stocks by 2022, carrying substantially more risk than the investor originally chose.

For a Silicon Valley household the drift is often faster. Company stock vests every quarter, and if it is not sold, the concentration grows regardless of what markets do. A rebalancing discipline provides a pre-agreed reason to sell some of it.

Calendar, threshold, or both

There are three common approaches. Calendar rebalancing reviews the portfolio on a fixed schedule, such as annually or semiannually. Threshold rebalancing acts only when an asset class moves beyond a set band, for instance five percentage points from target. A combined method checks on a schedule but trades only if a threshold has been breached. The SEC guide suggests reviewing every six to twelve months, or when an asset class moves by a predetermined percentage, and notes that rebalancing tends to work well when done relatively infrequently. Vanguard's analysis reached a similar conclusion, finding that the more effective approaches were neither too frequent nor too infrequent, with annual rebalancing holding up well because trading costs tend to rise during volatile periods.

No schedule is inherently correct, and none of them can identify a market top or bottom. Rebalancing is a rule for maintaining risk, not a signal for what to buy or sell.

The tax problem in a taxable account

In a 401(k) or IRA, rebalancing is nearly costless. In a taxable brokerage account, selling an appreciated asset triggers capital gains tax, and for California residents the state taxes those gains as ordinary income. For 2026, the federal long-term rate is 15% for most high earners and 20% above $545,500 of taxable income for single filers, plus the 3.8% net investment income tax where it applies. That cost is a genuine reason to rebalance thoughtfully rather than mechanically.

Several techniques reduce the tax friction. Directing new savings, dividends, and RSU proceeds toward underweight assets rebalances without selling anything. Doing the selling inside tax-advantaged accounts first, as Vanguard's research suggests, avoids realizing gains. Choosing high-basis lots when a sale is unavoidable limits the gain per share. Harvested losses elsewhere in the portfolio can offset rebalancing gains, subject to the wash sale rule, which disallows a loss if a substantially identical security is bought within 30 days before or after the sale, including in an IRA or a spouse's account. Charitable gifts of the most appreciated lots can serve the same purpose for households that give anyway.

The behavioral side

Rebalancing asks an investor to sell what has been doing well and buy what has been lagging. That is uncomfortable, and the discomfort is precisely why a written rule helps. DALBAR's 2026 investor behavior study reported that the average equity fund investor earned 17.16% in 2025 against 17.88% for the S&P 500, a gap of 0.72 percentage points that it described as among the smallest since 1985. A standing rebalancing policy removes some of the discretion that produces that gap.

Limits and trade-offs

Rebalancing does not guarantee a better outcome. In a long bull market, the disciplined rebalancer will trail a portfolio that simply let its winners run, and in a long decline, buying more of the falling asset feels wrong at every step. Transaction costs, bid-ask spreads, and taxes are real. What rebalancing offers is a portfolio whose risk stays roughly where it was designed to be, which is the condition under which the rest of the plan can work. This article is educational only and is not investment, tax, or legal advice; consider consulting a qualified professional about your circumstances.

Important Disclosures

Important Disclosures: Propulsion Capital Management is an investment adviser registered with the State of California Department of Financial Protection and Innovation. Registration does not imply a certain level of skill or training. This article is provided for general informational and educational purposes only and does not constitute investment, tax, legal, or accounting advice, nor an offer or solicitation to buy or sell any security or to adopt any particular investment strategy. The information is believed to be accurate as of the date of publication but is subject to change without notice; tax laws and regulations change frequently and their application depends on individual facts and circumstances. Nothing herein should be relied upon as a substitute for personalized advice from a qualified professional. Investing involves risk, including the possible loss of principal, and past performance is no guarantee of future results. Diversification does not ensure a profit or protect against loss. Any examples are hypothetical, are for illustrative purposes only, and do not reflect the experience of any client. Links to third-party websites are provided for convenience; Propulsion Capital Management does not endorse, and is not responsible for, the content of third-party sites. Propulsion Capital Management does not provide tax or legal advice; please consult your tax adviser or attorney regarding your specific situation.