Rebalancing Your Portfolio

You set a target allocation of 80% stocks and 20% bonds. After a strong year for stocks, your portfolio drifts to 88% stocks and 12% bonds. You now have significantly more risk than you planned for — and you're overweight in the asset class that's most likely to mean-revert after a strong run. Rebalancing means selling some stocks (which have gone up) and buying some bonds (which have lagged) to get back to your 80/20 target. It sounds simple. It is simple. But it's also one of the hardest things to do in investing because it requires selling winners and buying losers — the exact opposite of what your emotions tell you to do.

How Rebalancing Works

Rebalancing is the process of periodically realigning your portfolio's asset allocation back to your original target. There are two common approaches.

Calendar rebalancing — You rebalance on a fixed schedule, typically once or twice per year. On your chosen date, you check your allocation, calculate the deviation from your target, and make trades to restore it. This approach is simple, requires no market monitoring, and removes timing decisions entirely.

Threshold rebalancing — You rebalance whenever any asset class drifts more than a certain percentage from its target (commonly 5%). If your stock allocation drifts from 80% to 86%, you rebalance. This method responds to significant market moves but requires monitoring your portfolio.

Research shows that both approaches produce similar long-term results. Vanguard's analysis found that annual rebalancing provided the best risk-adjusted returns for most investors. More frequent rebalancing (monthly or quarterly) incurred unnecessary transaction costs and taxes without meaningful improvement. Less frequent rebalancing (every few years) allowed too much drift, increasing risk.

When you rebalance, you're systematically buying whatever has become cheap (it's below your target because it underperformed) and selling whatever has become expensive (it's above your target because it outperformed). This is a disciplined, automatic way to implement the "buy low, sell high" principle without relying on market predictions or emotional decisions.

In tax-advantaged accounts (401k, IRA), rebalancing has no tax cost — trade freely. In taxable accounts, you should rebalance with new contributions when possible (directing new money to the underweight asset class) to minimize taxable events. You can also rebalance by redirecting dividends and interest to the underweight allocation.

Why It Matters for Investors

Without rebalancing, your portfolio's risk level changes over time. After a long bull market, a 60/40 portfolio might drift to 80/20 — doubling your stock exposure and dramatically increasing your vulnerability to a crash. The 2008 crash dropped the S&P 500 by 38%. A portfolio that had drifted from 60/40 to 80/20 would have lost roughly 30% instead of 23%. That extra 7% — entirely avoidable with rebalancing — represents years of setback.

Vanguard's research shows that annual rebalancing reduces portfolio volatility by approximately 15-20% compared to a never-rebalanced portfolio, with minimal impact on long-term returns. In some periods, rebalancing actually improves returns because it forces you to sell overvalued assets and buy undervalued ones.

Rebalancing also provides a psychological benefit. It gives you a concrete, predetermined action to take during market turmoil. When stocks crash and bonds rally, your rebalancing plan says "sell bonds and buy stocks" — exactly the right move. Without a plan, you'd be making that decision under intense emotional pressure.

Real Example

Consider a portfolio that started 2007 with a 60% stock / 40% bond allocation and was never rebalanced. After the 2008 crash, it drifted to approximately 40% stocks / 60% bonds. Then during the 2009-2021 bull market, it gradually shifted to roughly 85% stocks / 15% bonds. The investor thought they were in a "balanced" portfolio but actually had nearly all their wealth in stocks — just in time for the 2022 bear market. A rebalanced portfolio would have sold stocks and bought bonds throughout the bull market, maintaining the 60/40 split. When 2022 hit, the rebalanced portfolio dropped about 16%, while the drifted portfolio dropped about 22%. Over the full period, both portfolios achieved similar total returns, but the rebalanced one achieved them with significantly less risk and dramatically fewer sleepless nights. The rebalancer never had to make a difficult decision — the system made every decision for them.