Portfolio Rebalancing: When, Why, and How to Realign Your Assets

How a Bull Market Quietly Made Millions of Portfolios Riskier

A portfolio that started 2015 at 60% stocks and 40% bonds looked very different by late 2021. Without rebalancing, U.S. equities' extraordinary gains pushed that same portfolio to roughly 80% stocks—an allocation carrying significantly more downside risk. When stocks dropped nearly 20% in 2022, the unbalanced portfolio suffered far larger losses than its owner expected. Rebalancing isn't exciting. It is essential.

Why Asset Allocations Drift

Every asset class grows (or shrinks) at a different rate. A portfolio with an intentional 60/40 stock-bond split will drift toward whichever asset outperforms. Between 2010 and 2020, U.S. stocks returned an annualized 13.9% while U.S. bonds returned 3.8%. By 2020, a $100,000 portfolio set to 60/40 in 2010 with no rebalancing held approximately $200,000 in stocks and $57,000 in bonds—a 78/22 split carrying stock market volatility far above the investor's original risk tolerance.

Rebalancing Methods Compared

Annual Rebalancing Is Often Enough

Research from Vanguard found that rebalancing annually or semi-annually produces similar risk-adjusted outcomes to more frequent rebalancing—while generating fewer taxable events. The T. Rowe Price research group analyzed data from 1985 to 2018 and found a 5% drift threshold with annual monitoring offered the best balance of risk control and transaction costs.

The Tax Dimension of Rebalancing

In taxable accounts, selling appreciated assets triggers capital gains taxes. Strategies to minimize the tax drag include:

• Use new contributions: Direct fresh cash into underweighted asset classes instead of selling overweighted ones
• Rebalance in tax-advantaged accounts first: 401(k)s and IRAs allow selling and buying without immediate tax consequences
• Tax-loss harvesting: Sell losing positions to realize losses that offset gains elsewhere in the portfolio
• Dividend routing: Direct dividend payments into the underweighted asset class automatically

A portfolio with $5,000 in unrealized gains from an overweighted stock position will owe $750 at the 15% long-term capital gains rate if sold. In a Roth IRA, the same rebalancing trade costs nothing.

Practical Rebalancing Example

Does Rebalancing Improve Returns?

The evidence is mixed—but the purpose of rebalancing was never primarily return enhancement. A 2022 Vanguard study spanning 1988 to 2021 found annual rebalancing of a 60/40 portfolio produced slightly lower returns than a never-rebalanced portfolio (because stocks outperformed bonds over that period) but with meaningfully lower volatility and maximum drawdown.

Rebalancing forces an investor to systematically sell high and buy low—reducing risk exposure during bull markets and increasing it after crashes. A portfolio that never rebalanced would have entered the 2008 financial crisis with far more stock exposure than intended.

Robo-Advisors and Automatic Rebalancing

Betterment, Wealthfront, and Schwab Intelligent Portfolios all offer automatic rebalancing as a standard feature. Betterment uses continuous threshold monitoring—tracking allocations daily and rebalancing whenever drift exceeds set boundaries. This removes behavioral bias (hesitating to sell winners) and ensures consistency. For investors who don't want to monitor portfolios manually, automatic rebalancing through a robo-advisor is a sound alternative.

Disclaimer: This article is for informational purposes only and does not constitute investment advice. Tax rules vary by individual situation. Consult a qualified financial advisor and tax professional before making portfolio decisions.