What does rebalancing a portfolio mean?

Rebalancing means bringing a portfolio back to its target mix after market moves have shifted it. For example, if a 60% stock target has grown to 65% after a strong run, rebalancing moves it back to 60%.

How often should a portfolio be rebalanced?

There is no single rule. Some people check on a schedule, such as every six or twelve months, and others act only when the mix drifts past a set band. Investor.gov notes that rebalancing tends to work best when done relatively infrequently.

Does rebalancing trigger taxes?

Selling an investment for more than you paid can create a taxable gain in an ordinary account, depending on where you live. Trades inside many tax-advantaged accounts are generally not taxed at the time. Directing new contributions to the lagging part avoids selling altogether.

Portfolio rebalancing: how and when to reset your mix

What portfolio rebalancing is, how drift changes your risk, calendar vs threshold rebalancing, using new money to rebalance, and the costs and taxes.

Part of the Investing Foundations track on Agenticks. About 9 minutes, written for a beginner reader.

Read first: Asset allocation: choosing your mix of stocks, bonds and cash.

Last reviewed 2026-11-08.

Key takeaways

Markets push a portfolio away from its target mix over time. That drift quietly changes how much risk you carry.
Rebalancing resets the mix by trimming what has grown and adding to what has lagged, or by sending new money to the lagging part.
Calendar rebalancing checks on a schedule; threshold rebalancing acts when the mix drifts past a set band. Doing it rarely is usually enough.
Selling to rebalance can bring trading costs and, in a taxable account, tax on gains, so new contributions are often the cheapest tool.

In the asset allocation lesson you saw how the split between stocks, bonds and cash sets most of a portfolio's swings. The trouble is that a mix does not stay put. Different investments grow at different speeds, so after a strong year for stocks a 60/40 portfolio might be 65/35, and after a weak one it might be 55/45. Nobody decided that. It just happened. This slow shift is called portfolio drift. Rebalancing is bringing the portfolio back to its target mix. The point is not to squeeze out extra return. It is to keep your risk where you chose to put it, because a portfolio that has drifted to more stocks than you planned will also fall harder than you planned when the next bad year arrives.

Worked example: drift, then two ways back to 60/40

A $100,000 portfolio starts at 60% stocks and 40% bonds. Over a year stocks rise 25% and bonds stay flat.

Stocks after the year (60,000 x 1.25)	$75,000
Bonds after the year (40,000 x 1.00)	$40,000
New mix (75,000 / 115,000)	65.2% stocks / 34.8% bonds
Stocks at a 60% target (115,000 x 0.60)	$69,000
Way 1: sell stocks, buy bonds (75,000 - 69,000)	move $6,000
Way 2: add new money to bonds only (bonds 50,000 of 125,000 = 40%)	add $10,000
Either way, back to	60% stocks / 40% bonds

Illustrative returns. Trading costs and taxes are left out here and covered below.

Five percentage points of drift may not sound like much, but it keeps building through a long run of good years. Investor.gov gives the example of a portfolio that starts at 60% stocks and grows to 80% stocks on market gains alone. By then the portfolio behaves like a much more aggressive one than its owner signed up for, and the risk and return tradeoff says the next fall will be correspondingly deeper. Rebalancing also has an awkward feel to it. It means trimming whatever has been doing well and adding to whatever has lagged. That runs against instinct, which usually wants more of the winner and less of the loser. A rule written down in advance makes it easier to act when the moment comes.

There are two common ways to decide when to rebalance. Calendar rebalancing checks the mix on a fixed schedule, such as every six or twelve months, and resets it then. Threshold rebalancing ignores the date and acts only when an asset class drifts past a set band, for example more than 5 percentage points away from its target. In the example, a 5-point band around a 60% stock target means doing nothing until stocks pass 65% or fall below 55%. Many people combine the two: look on a schedule, but only trade if the drift is past the band. Whichever rule is chosen, Investor.gov notes that rebalancing tends to work best when done relatively infrequently. Checking every week mostly produces more trades and more costs, not a better result. The width of the band is a trade-off of its own. A very narrow band, say one point, means trading after every ordinary wobble. A very wide one, say fifteen points, lets a 60% stock target reach 75% before anything happens, which defeats the purpose. Small holdings often get a band sized to them instead of a flat number of points: for a 10% cash target, a band of 2.5 points either way is a quarter of the target, while 5 points would be half of it.

Rebalancing works in both directions, and the hard direction is after a fall. Take the same $100,000 at 60/40 and give it a bad year instead: stocks fall 30% and bonds gain 3%. Stocks drop to $42,000 and bonds rise to $41,200, so the portfolio is worth $83,200 and is only about 50% stocks. Getting back to 60% means holding about $49,900 in stocks, so roughly $7,900 moves from bonds into stocks. On paper that is buying stocks after they have fallen. In real life it means buying the thing that just lost money, while the news is at its worst, which is exactly why a rule set in a calmer moment helps. This also shows what rebalancing does and does not do to returns. Through a long rise in stocks, trimming them on the way up can leave you with less than letting the portfolio drift would have. That is not a flaw. It is the price of holding the level of risk you chose instead of a higher one you never agreed to.

New money is the cheapest way to rebalance

If you are still adding money, send it to whatever is below target. In the example, $10,000 of new contributions went entirely to bonds and restored 60/40 without selling a single share, so there was no trading cost on a sale and no gain to pay tax on. Dividends and interest can be pointed the same way.

When rebalancing does mean selling, two costs come with it. The first is trading costs: commissions where they apply, and the bid-ask spread on every trade. The investment fees lesson covers both. The second is tax. In an ordinary taxable account, selling something for more than you paid can create a capital gain that is taxable, under rules set by the IRS in the US, the Canada Revenue Agency, and HMRC in the UK. Trades made inside many tax-advantaged accounts are generally not taxed at the time. How much any of this matters depends on your country, your accounts and your own situation, and the rules change, so the official pages and the accounts and tax track are the place to check details. This is one more reason people lean on new contributions, and on rebalancing inside sheltered accounts first, before selling in a taxable one. Some funds do this job for you. A balanced or target-date fund holds a set mix and rebalances it internally, and a target-date fund also shifts that mix towards bonds as its target year approaches.

Put the steps of a threshold rebalance in a sensible order.

Write down the target mix and the band, for example 60/40 with a 5-point band
Check what each part of the portfolio is worth today
Compare each part with its target and see if any is past the band
Send new contributions, dividends and interest to the part below target
If still past the band, sell some of the overweight part and buy the underweight part

You can rebalance a portfolio on paper

You can measure drift, work out what a rebalance takes, choose between calendar and threshold rules, and explain why new money and sheltered accounts keep costs down.

Check your understanding

What is the main purpose of rebalancing?: To keep the portfolio's risk close to the mix you chose. Rebalancing is about controlling risk. Any effect on returns is a side effect, not the goal.
A $100,000 portfolio starts at 60% stocks and 40% bonds. Stocks rise 25% and bonds stay flat. Roughly what share is now in stocks?: About 65%. Stocks grow to $75,000 out of $115,000 in total, which is about 65.2%.
In the same example, how much new money sent only to bonds would bring the mix back to 60/40 without selling anything?: $10,000. Bonds become $50,000 of $125,000, which is exactly 40%, and stocks stay at $75,000, which is 60%.
Which is a threshold rule rather than a calendar rule?: Rebalance whenever stocks drift more than 5 percentage points from target. A threshold rule acts on the size of the drift, whatever the date.

Common questions

What does rebalancing a portfolio mean?: Rebalancing means bringing a portfolio back to its target mix after market moves have shifted it. For example, if a 60% stock target has grown to 65% after a strong run, rebalancing moves it back to 60%.
How often should a portfolio be rebalanced?: There is no single rule. Some people check on a schedule, such as every six or twelve months, and others act only when the mix drifts past a set band. Investor.gov notes that rebalancing tends to work best when done relatively infrequently.
Does rebalancing trigger taxes?: Selling an investment for more than you paid can create a taxable gain in an ordinary account, depending on where you live. Trades inside many tax-advantaged accounts are generally not taxed at the time. Directing new contributions to the lagging part avoids selling altogether.

Terms defined in this lesson

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Written and reviewed by the Agenticks Learn editorial team. How we write and check lessons.

Agenticks Learn is general education. It is not financial, investment, tax or legal advice, it does not take your situation into account, and nothing on it is a recommendation to buy, sell or hold any security or to open any account. Examples use illustrative numbers. Investing involves risk, including losing money you put in, and past performance does not predict future results. Tax rules and limits change; the official sources linked in each lesson are the final word.