What Is Portfolio Rebalancing and How Often Should You Do It?

Written by Jim Norris · NorrisAI AlphaLens · Updated August 2026

Quick answer: Portfolio rebalancing means restoring your target asset allocation after market movements have shifted it away from your intended mix. If stocks rise significantly, they become a larger percentage of your portfolio than you intended — rebalancing sells some stocks and buys other assets to restore the balance. It enforces buy-low, sell-high discipline automatically and keeps your portfolio's risk profile consistent with your goals.

Why portfolios drift

Suppose you target 70% stocks and 30% bonds. After a strong stock market year, stocks might represent 80% of your portfolio while bonds have shrunk to 20%. Your portfolio is now more aggressive than you intended — taking more risk than your original allocation reflected. If stocks then fell 30%, you'd lose more than if you had stayed at 70%.

Rebalancing corrects this drift before it creates a mismatch between your intended risk profile and your actual one.

The two main rebalancing approaches

Calendar-based: rebalance at fixed intervals — annually, semi-annually, or quarterly. Simple to implement and creates consistent discipline regardless of market conditions. Annual rebalancing is sufficient for most investors and minimizes transaction costs and tax drag.

Threshold-based: rebalance whenever any asset class drifts more than a set percentage from target — say, 5% away from the intended allocation. More responsive to market moves but requires more monitoring. A 5% threshold triggers rebalancing about as often as annual calendar-based approaches on average.

A hybrid approach — check annually, but also rebalance immediately if any position drifts more than 10% from target — captures the benefits of both.

Tax-efficient rebalancing

Selling appreciated assets to rebalance triggers capital gains taxes in taxable accounts. Several approaches minimize this cost:

Rebalance through new contributions. Direct new investment money toward underweighted assets rather than selling overweighted ones. This brings the portfolio back toward target without triggering taxes.

Reinvest dividends and income selectively. Reinvest dividends from overweighted assets into underweighted ones.

Prioritize rebalancing in tax-advantaged accounts. Trading within an IRA or 401(k) has no immediate tax consequences. Do the heavy rebalancing there and minimize taxable account transactions.

Pair with tax-loss harvesting. When rebalancing requires selling in a taxable account, look for positions in the same asset class with unrealized losses that can offset the gains.

Professor Burton Malkiel of Princeton University recommends annual rebalancing as a discipline that improves risk-adjusted returns over time — not because timing is perfect, but because it enforces consistency and prevents the natural human tendency to let winners run until they dominate the portfolio at exactly the wrong time. — A Random Walk Down Wall Street, W.W. Norton

Rebalancing individual stock portfolios

For portfolios of individual stocks rather than index funds, rebalancing requires more nuance. A stock that's grown to 25% of your portfolio from a target 5% has done so because it's been an exceptional performer — not necessarily because its risk profile has changed. The question is whether the stock is still attractively valued or whether the run-up has pushed it to fair or overvalued territory.

The right framework: rebalance when a stock's weight has grown to an uncomfortable concentration level AND it no longer offers an adequate margin of safety. If it's grown to 15% but is still clearly undervalued, trimming to 10% may be premature. If it's grown to 15% and is now fully valued, trimming makes sense regardless of position size target.

Howard Marks has noted that the discipline of rebalancing — selling what has risen and buying what has fallen — is psychologically difficult but structurally sound. It forces investors to act counter-cyclically rather than with the crowd, which is the essence of rational long-term portfolio management.

How AlphaLens supports rebalancing decisions

The Portfolio Risk & Fit framework (framework #6) tracks how individual positions have grown relative to your target allocations and flags concentration risk. The Fair Value Stress Test provides the intrinsic value assessment needed to decide whether a grown position should be trimmed (now fairly valued) or held (still undervalued despite the run-up). Together they make rebalancing decisions evidence-based rather than purely mechanical.

Where to go deeper

For a detailed walkthrough of each research framework, see the complete guide to all 15 AlphaLens frameworks.

For definitions of investing terms, see the AlphaLens investing glossary.