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Portfolio Rebalancing: Calendar vs. Threshold Strategies

Here's how to keep your portfolio's original mix from drifting too far off target.

Why rebalancing matters

Over time, assets that go up in value take up a larger share of your portfolio while assets that fall shrink, quietly pulling your allocation away from the mix you originally chose. A portfolio that started at 60/40 stocks-to-bonds can drift to 70/30 or 80/20 after a strong run in stocks, exposing you to more risk than you signed up for unless you periodically bring it back in line.

Calendar (periodic) rebalancing

This approach checks and adjusts your allocation on a fixed schedule -- quarterly, semiannually, or once a year. It is easy to turn into a habit and removes emotion from the decision, but if the market has not moved much by your scheduled date, you may end up paying trading costs for a trim that barely matters.

Threshold (band) rebalancing

Here you only rebalance when an asset drifts a set distance from its target -- commonly plus or minus five percentage points. This cuts down on unnecessary trades since you act only when the market has actually moved meaningfully, but it requires you to check your allocation more often, and choosing too narrow a band causes frequent trading while too wide a band lets risk drift too far before you notice.

The costs that come with rebalancing

Because rebalancing means buying and selling, it triggers trading commissions, the bid-ask spread, and -- in a taxable account -- capital gains tax on anything you sell at a profit. Rebalancing inside a tax-advantaged retirement account avoids the tax bill entirely, which is one reason many investors prefer to do their rebalancing trades there when possible.

Rebalancing with new contributions

Instead of selling anything, you can steer new money -- a monthly paycheck contribution, for example -- toward whichever asset has fallen below its target weight. If you are investing steadily over time, this lets you nudge your allocation back toward target without triggering a taxable sale or extra trading costs.

A caution worth keeping in mind

Rebalancing is a risk-management technique, not a way to boost returns. Because it involves trimming what has gone up and adding to what has lagged, it can actually reduce your gains during a long bull run in one asset class. Its job is to keep your risk level where you intended it to be, not to maximize performance.

Rebalancing assumes you already have a target mix

Rebalancing only makes sense once you have decided how to split your money between higher-risk assets (like stocks) and lower-risk ones (like bonds or cash). If you have not settled on that target allocation yet, that decision -- based on your goals, time horizon, and risk tolerance -- comes first; rebalancing is simply the maintenance step that keeps you at whatever mix you already chose.

General information, not financial advice

This page explains rebalancing approaches as general financial education, not investment advice. The right rebalancing frequency, band width, and timing depend on your personal finances, tax situation, and goals, so treat this as background for your own research or a conversation with a financial professional rather than a specific recommendation.

Frequently Asked Questions

How often should I rebalance?

There's no single correct answer. Rebalancing too often raises trading costs and taxes, while rebalancing too rarely lets risk drift too far from your target. A common approach combines an annual or semiannual check with a threshold rule, so you act on schedule but also respond if the market moves sharply in between.

Does rebalancing always improve returns?

No. Rebalancing manages risk by returning your portfolio to its intended level, not by maximizing return. During a long rally in one asset class, it can actually mean trimming some of your gains earlier than you would have otherwise.