TL;DR: Rebalancing restores a target allocation after market moves drift it. In the worked example below, a $100,000 portfolio with a 60 percent stocks and 40 percent bonds target drifts to $68,000 in stocks and $32,000 in bonds. The targets are $60,000 and $40,000, so rebalancing sells $8,000 of stocks and buys $8,000 of bonds. No forecast is involved. You are resetting risk to the level you originally chose, not predicting which asset will do better next.
Key Takeaways
- Drift is automatic: the asset that performs best becomes a larger share, so an unrebalanced portfolio slowly takes more risk than its owner selected.
- The arithmetic is target value minus current value for each holding. A positive gap is a buy, a negative gap is a sell.
- Two common triggers are a calendar schedule, such as once a year, and a threshold, such as rebalancing when any allocation is five percentage points from target.
- Rebalancing in a taxable account can create taxable gains. Doing it first with new contributions, dividends, and tax advantaged accounts is a common way to reduce that cost.
- Rebalancing does not guarantee higher returns. Its primary job is risk control, keeping the portfolio you actually hold aligned with the portfolio you intended.
What is rebalancing, in one example?
All numbers in this section are illustrative. Start with $100,000 split to target: 60 percent stocks is $60,000, and 40 percent bonds is $40,000. Stocks then rise while bonds stay roughly flat, and a year later the account holds $68,000 in stocks and $32,000 in bonds. The total is still $100,000 in this simplified example, chosen so the arithmetic is easy to follow. In a real account the total would also have moved.
The current weights are $68,000 divided by $100,000, which is 68 percent stocks, and 32 percent bonds. The portfolio is now eight percentage points more aggressive than planned. Target values at the current total are unchanged: $60,000 in stocks and $40,000 in bonds. The stock gap is $60,000 minus $68,000, which is negative $8,000, meaning sell $8,000. The bond gap is $40,000 minus $32,000, which is positive $8,000, meaning buy $8,000. One sale funds the purchase, and the allocation is back to 60 and 40.
That is the whole mechanism. With more holdings, you repeat the same target minus current calculation for each line, as you would when you track portfolio performance against a benchmark and compare weights side by side.
How often should you rebalance?
A calendar method picks a date, commonly annually, and resets weights then regardless of how far they drifted. It is simple and predictable, and it can mean trading in a year when drift was tiny. A threshold method trades only when drift crosses a set band, for example five percentage points on a major allocation. It trades less often in quiet markets and faster in volatile ones, but it requires checking weights regularly, not just on one date.
A hybrid is common in practice: check on a schedule, trade only if a threshold is crossed. Whichever method you choose, write it down in advance. A rule chosen in calm conditions prevents the two emotional errors: refusing to trim a winner during a boom, and refusing to buy an asset that has fallen during a panic. Rebalancing mechanically forces a small amount of selling high and buying low relative to your own holdings, which is a discipline benefit, not a return promise.
Can you rebalance without selling?
Often, partly. New contributions can be directed entirely to the underweight asset until weights recover. Dividends and interest can be taken as cash and reinvested in the underweight side instead of automatically reinvesting into the same holding. Required withdrawals, for investors taking them, can be sourced from the overweight side. These cash flow methods are slower than a direct sale and purchase, and in a fast market they may not close a large gap, but they avoid realising taxable gains in a taxable account and reduce transaction costs.
Where you hold both taxable and tax advantaged accounts, many investors view the allocation across all accounts combined, and place trades inside the tax advantaged accounts where possible. Tax treatment varies by country and account type, so treat that as a planning question for your own rules, not as a universal instruction from this guide.
What does rebalancing not do?
It does not fix a target that was wrong for you. If a 60 and 40 split no longer matches your time horizon or your ability to tolerate a fall, the answer is to change the target deliberately, not to keep restoring it. It also does not protect against a fall in both stocks and bonds at the same time, which has happened historically. And it does not need doing weekly. Frequent rebalancing adds costs and taxes while chasing noise, because weights move a little every day by design. The compound growth calculator guide shows why keeping costs low over long periods matters more than small timing adjustments.
Review your weights, compare them to your written target, and trade only when your chosen rule says to. That boring loop is the entire strategy, and its value is that it still works on the days when doing it feels uncomfortable.
Sources and method
- Target keyword: "portfolio rebalancing" from .saeo/keywords.yaml candidate added 2026-10-25. No search volume or difficulty figure is claimed.
- All portfolio figures are labelled illustrative examples. Arithmetic verified for this draft on 2026-10-25: $68,000 plus $32,000 equals $100,000, target stocks $60,000 and bonds $40,000 at 60 and 40 percent, sell $8,000 of stocks and buy $8,000 of bonds.
- Internal links checked against existing drafts in this folder on 2026-10-25: track-portfolio-performance-vs-benchmark, compound-growth-calculator.
