How does portfolio rebalancing work, step by step?

What does rebalancing a portfolio mean?#

Investor.gov defines rebalancing as bringing a portfolio back to its original asset allocation mix^[1]. Your asset allocation is the split you chose between categories such as stocks, bonds and cash — for example, 60% stocks and 40% bonds. If you have not chosen one yet, start with asset allocation basics.

The reason it is needed is simple: over time, some investments will grow faster than others, and holdings may drift out of line with your goals^[1]. An SEC publication puts the purpose in one sentence: by rebalancing, you'll ensure that your portfolio does not overemphasize one or more asset categories, and you'll return your portfolio to a comfortable level of risk^[2].

Why does a portfolio drift away from its target?#

Because each part earns a different return. Suppose you start with $10,000 split 60/40 between stocks and bonds. In one hypothetical year, stocks gain 20% and bonds gain 2%. You did nothing, yet your mix changed.

After two such years, the portfolio holds about two-thirds stocks without you ever deciding that. Since bonds are generally less volatile than stocks^[3], the portfolio now carries more risk than the one you designed. Drift can also go the other way: after a bad year for stocks, the mix leans more toward bonds than you intended.

How do you rebalance a portfolio, step by step?#

The SEC's beginners' guide lists three ways to get back to target: sell investments from over-weighted categories and use the proceeds to buy under-weighted ones; buy new investments for under-weighted categories; or, if you are making regular contributions, change where they go until the portfolio is back in balance^[3]. The routine below puts those options in order.

1. 1

   Write down your target mix

   For example, 60% stocks and 40% bonds. Without a written target there is nothing to rebalance back to.

2. 2

   Pick your trigger in advance

   Choose a calendar date (for example, once a year) or a drift limit (for example, 5 percentage points away from target). Decide before markets move, not after.

3. 3

   Check today's weights

   Add up the value of each category across all your accounts and divide by the total. In the example, stocks are at 63.83%.

4. 4

   Use new money first

   If you are adding money anyway, send it to the underweight category. In the example, adding $720.00 to bonds restores 60/40 exactly, with no selling.

5. 5

   Buy or sell the difference if needed

   If new money is not enough, sell part of the overweight category and buy the underweight one. In the example, selling $432.00 of stocks and buying $432.00 of bonds restores 60/40.

6. 6

   Check fees and taxes before you trade

   The SEC advises considering whether your method will trigger transaction fees or tax consequences before you rebalance.

7. 7

   Record what you did

   Note the date, the weights before and after, and why. It keeps the next check consistent.

Should you rebalance on a calendar or when weights drift past a limit?#

Both approaches appear in SEC material. Many financial experts recommend rebalancing on a regular interval, such as every six or twelve months, and the advantage is that the calendar reminds you when to look^[3]. Others recommend rebalancing only when the weight of an asset class moves more than a certain percentage that you've identified in advance^[3].

In the worked example, stocks drifted 3.83 percentage points after one year — inside a 5-point band, so a threshold investor would wait. After the second year the drift was 7.49 points, outside the band. Whichever rule you choose, the SEC adds that rebalancing tends to work best when done on a relatively infrequent basis^[2].

What costs and taxes can rebalancing trigger?#

The SEC's guide says that before you rebalance, you should consider whether your method will trigger transaction fees or tax consequences^[3]. Every sale can carry a trading cost, and some mutual funds charge a back-end load when you redeem shares^[4]. Our note on investment fees explains the common types.

Taxes depend on the account and the country. In the U.S., the IRS explains that the difference between your adjusted basis (roughly, what you paid) and what you receive from a sale is a capital gain or capital loss^[5]. Gains on assets held one year or less are short-term, and net short-term gains are taxed as ordinary income^[5]. Selling winners in a taxable account to rebalance can therefore create a tax bill. Rules differ by country, and tax-advantaged retirement accounts have their own rules.

This is one reason the contribution method is attractive: when you only buy, nothing is sold, so no gain is realized. See the capital gain glossary entry for the basic terms, and the rebalancing definition for a one-paragraph summary.

What mistakes do beginners make?#

1. Rebalancing by feel instead of by rule

   Deciding after a scary headline turns rebalancing into market timing. Set the date or the drift limit in advance and follow it.

2. Looking at one account instead of all of them

   If you hold investments in several accounts, the mix that matters is the combined one. Add everything up before deciding what is overweight.

3. Ignoring taxes and fees

   Selling in a taxable account can trigger capital gains tax, and frequent trades can add costs. Use new contributions first where you can.

4. Rebalancing too often

   Trading every small wiggle adds cost without much benefit. SEC material notes that rebalancing tends to work best when done relatively infrequently.