Portfolio rebalancing: when to act, what to trade, and a worked example

Rebalancing is not a way to make a portfolio earn more. It is a way to bring its risk and mix back toward a target you chose. If one holding grows faster than the rest, its share of the portfolio rises even if you never buy another share. The U.S. SEC describes rebalancing as bringing a portfolio back to its original asset-allocation mix, while noting that the right allocation depends on the investor’s goals and circumstances (Investor.gov: asset allocation and rebalancing).

How do you measure portfolio drift?

Compare each holding’s current weight with its target, in percentage points. Choose target weights that add to 100%. For each holding, compare its current market value with the portfolio total to find its current weight:

current weight = holding value ÷ total portfolio value × 100

The difference between current and target weight is drift, measured in percentage points (pp). A holding at 32% against a 30% target is +2 pp overweight. A holding at 12% against a 15% target is −3 pp underweight. That difference is not the same as a 2% or 3% investment return.

How do you rebalance a $30,000 portfolio?

Work out each holding’s target value, then trade the difference — or direct new cash to what is underweight. Suppose the portfolio holds $18,000 in U.S. stocks, $4,000 in bonds and $8,000 in international stocks. Its targets are 55%, 30% and 15%.

Holding	Current value	Current weight	Target value	Trade to target
U.S. stocks	$18,000	60.0%	$16,500	Sell $1,500
Bonds	$4,000	13.3%	$9,000	Buy $5,000
International stocks	$8,000	26.7%	$4,500	Sell $3,500

The full rebalance sells $5,000 and buys $5,000, returning the portfolio to its target weights before costs, price changes and taxes. The trades are arithmetic, not a recommendation that these targets or holdings are appropriate.

If instead you contribute $5,000 and do not sell, the portfolio becomes $35,000. The new target values are $19,250, $10,500 and $5,250. U.S. stocks and bonds are now below those targets by $1,250 and $6,500, so a proportional buy-only allocation puts about $806 into U.S. stocks and $4,194 into bonds. The weights move closer to target but do not reach it. A buy-only approach avoids realizing gains through those sales, but it cannot always correct a large drift quickly.

Try your own values in the free portfolio rebalancing calculator. It shows both the full-trade plan and a new-cash-only plan in your browser; your inputs are not sent to the site.

Should you rebalance on a schedule or at a threshold?

Either can work, and many investors combine them. Calendar rebalancing means checking or trading at a set interval. Threshold rebalancing means acting when a holding moves outside a band around its target. A practical compromise is to review periodically and trade only when the drift crosses a threshold. The SEC notes that investors commonly rebalance at regular intervals or when an allocation has shifted by a predetermined amount; it does not endorse one formula as right for everyone (same Investor.gov guide).

This calculator flags the 5/25 rule: a position is off band when it differs by more than 5 percentage points or more than 25% of its target weight. For a 40% target, the relative threshold is 10 pp, so the 5 pp threshold is tighter. For a 4% target, 25% is 1 pp, so the relative threshold is tighter. These are the calculator’s screening bands, not a universal standard or personalized advice.

Questions investors ask

How often should I rebalance?

There is no schedule that fits every portfolio. A calendar review can help you notice drift, while a threshold can help avoid trading for small changes. Consider your goals, account type, transaction costs and tax consequences before deciding whether to trade.

Can I rebalance without selling?

Often you can move closer to target by directing new contributions or cash flows toward underweight holdings. This does not guarantee that you will reach target weights, and it does not remove other investment risks. In a taxable account, selling appreciated investments may have tax consequences; get advice for your own situation.

Does rebalancing improve returns?

Not necessarily. Its purpose is to maintain an allocation, not to predict which investment will perform best. It can involve costs, taxes and the risk of selling an asset that later rises. Review your plan and the trade-offs, rather than treating any calculator output as an instruction.

For related concepts, see the guides to portfolio health and concentration and risk measures such as drawdown and volatility, or review the rebalancing glossary definition. Educational information only—not investment or tax advice.