Pro Investor Academy
LESSON 5.5
6 min learning time

Rebalancing

Rebalancing resets a portfolio back to its target weights after markets move it away from them.

The short answer

Rebalancing means adjusting a portfolio back toward its target allocation after market movements have caused it to drift, typically by trimming what has grown into an oversized share and adding to what has fallen behind. It is a form of risk control that keeps a portfolio's risk level consistent with a plan, not an attempt to time the market.

Learning objectives

  • Explain what allocation drift is and why it happens without any new purchases
  • Compare calendar-based rebalancing with threshold-based rebalancing
  • Explain why rebalancing is risk control rather than market timing
  • Describe, in general terms, the tax and cost considerations relevant to rebalancing

What drift is

A portfolio built with target weights — say, a certain split between stock funds and bond funds — will drift away from those weights simply because different holdings grow at different rates.

Left alone long enough, a portfolio that started at a chosen risk level can end up meaningfully riskier or more conservative than intended, without a single new decision having been made.

Calendar versus threshold rebalancing

Calendar rebalancing checks and resets the portfolio on a fixed schedule — for example, once a year. It is simple and easy to stick to.

Threshold rebalancing instead acts whenever a holding drifts beyond a set band, such as five percentage points from its target. It responds to how much drift actually occurred rather than to the passage of time. Neither approach is inherently superior; the point is choosing one and following it consistently.

What rebalancing is not

Rebalancing is not a prediction that any asset class is about to rise or fall. Trimming an oversized holding is not a bet against it, and adding to a smaller one is not a bet in its favor.

The purpose is to keep the portfolio's overall risk consistent with a plan chosen in advance, regardless of which asset happens to have performed well recently.

Cost and tax considerations, in general terms

Selling appreciated holdings in a taxable account can create a taxable event, and trading has costs even when small. These are real considerations, not reasons to avoid rebalancing altogether.

Directing new contributions toward the underweighted portion of a portfolio can rebalance it gradually without selling anything, and using tax-advantaged accounts for rebalancing trades can reduce tax friction. Specific tax questions belong to a qualified professional, since they depend on individual circumstances.

Two rebalancing approaches
Calendar rebalancingReset on a fixed schedule (e.g. annually)
Threshold rebalancingReset when drift passes a set band (e.g. 5 points)

Neither approach is presented as superior; consistency matters more than which is chosen.

Key concepts

Select a term to read its definition.

  • Rebalancing

    Adjusting holdings back toward intended proportions, ideally using new contributions first.

    View in the glossary
  • Drift

    When a portfolio's mix moves away from its target because some holdings grew faster than others.

    View in the glossary
  • Target allocation

    The intended mix of investments, for example 80% stocks and 20% bonds.

    View in the glossary
  • Taxable eventU.S. rule

    An action that can create a tax bill, such as selling at a gain or receiving a dividend in a taxable account. These examples follow U.S. rules; other countries differ.

    View in the glossary
See the full glossary

Why this matters

Without rebalancing, a portfolio's risk level silently drifts to whatever recent market moves created, rather than staying at the level you actually chose.

Common mistakes

  • Treating a large recent gain as a signal to abandon the target allocation rather than trim back to it
  • Ignoring the tax impact of selling in a taxable account when a contribution-based rebalance could have worked instead

Check your understanding

No score is recorded. This is only here to test whether the lesson landed.

1. What does allocation drift describe?
2. Hypothetical: your written policy targets 60% stocks / 40% bonds with a ±5-point band. After a strong year the taxable account is 68/32, and you add $500 a month. Which plan fits this lesson best?
3. A portfolio's target is 60% stocks and 40% bonds, but after a strong run in stocks it is now 75% stocks and 25% bonds. What would a disciplined rebalancing approach suggest?

0 of 3 answered. Answer every question to see the answers.

Key takeaways

  • Allocation drift happens automatically as different holdings grow at different rates
  • Calendar and threshold rebalancing are two disciplined ways to reset a portfolio; consistency matters more than which is chosen
  • Rebalancing is risk control aimed at a chosen plan, not an attempt to predict or time the market
  • New contributions can rebalance a portfolio gradually and sometimes with less tax friction than selling

Optional next reading

Not required for this level or the certificate.

Written by
Pro Investor Academy Research Team
Content type
Educational article
Published
2026-09-13
Last reviewed
2026-09-13

Sources

Position SizingBuilding an Investment Policy

Educational content only. This lesson is not investment, tax or legal advice and does not recommend buying or selling any specific investment. All investing involves the risk of loss.