Portfolio Rebalancing: Bringing the Mix Back in Line

Put a date on your calendar. The first trading day of the year works. So does your birthday. On that day, open every account, add up what’s in stocks and what’s in bonds, and compare the split with the one you meant to have.

It won’t match. It almost never does. Some holdings grow faster than others, and each month the faster ones take up a slightly bigger share of the total, so a portfolio you set up carefully can end up, a few good years later, holding far more of its riskiest asset than you ever decided on.

How drift happens

Take a hypothetical $100,000 portfolio with a target of 60% stocks and 40% bonds. That’s $60,000 and $40,000. Suppose stocks have a good stretch while bonds hold flat. The account grows to $115,000, holding $75,000 of stocks against $40,000 of bonds. Stocks are now about 65% of the portfolio.

You didn’t choose 65%. The market did.

The trade feels backward. You’re selling what did well and buying what lagged. That’s the point of it, because the 60/40 split was your decision about how much a stock market fall could be allowed to hurt, and at 65/35 a fall hurts more than you signed up for. Notice that the targets come from today’s total; aiming back at the original $60,000 would sell too much.

Two ways to decide when

Calendar rebalancing is the simple one. Once a year, on the date you picked, you trade back to target whatever the numbers say. It’s easy to remember and hard to overthink.

Threshold rebalancing waits for a weight to drift past a band you set in advance. With a 60% stock target and a band of 5 percentage points, you’d act when stocks rise above 65% or fall below 55%, and leave the portfolio alone in between. The 65.2% in the example just crosses that line. A 62% reading wouldn’t.

Bands mean fewer trades in quiet years and quicker action in wild ones. They also need you to check more often. Some investors combine the two, looking once or twice a year and trading only if a band has been crossed. The band width is your choice; the 5 points here is an example.

Taxes and a gentler method

Where the money sits matters. Inside a retirement account such as an IRA or a 401(k), selling one fund to buy another doesn’t create a tax bill at the time of the trade. In a taxable brokerage account, selling a holding that has risen realizes the gain, and you may owe tax on it for that year.

That’s a reason to rebalance with new money first. Suppose you add $10,000 to the account above and put all of it into bonds. The mix becomes $75,000 in stocks and $50,000 in bonds, a $125,000 total, which is 60/40 exactly. Nothing was sold. A smaller contribution does part of the job, and sending each new one to the underweight side keeps closing the gap. Dividends and bond interest can be pointed the same way: take them as cash and invest them where the portfolio is short, if your account lets you switch off automatic reinvestment for the holding that paid them.

The explainer on how dividends are taxed covers the income side. For the growth side, the dividend reinvestment calculator shows how reinvesting changes a balance.

What rebalancing does and doesn’t do

Rebalancing is a risk control. It keeps the portfolio near the level of risk you picked. It makes no promise about returns. In a long run where stocks keep beating bonds, the rebalanced portfolio can end with less than one left to drift, because it kept trimming the winner. You accept that in exchange for a portfolio that behaves the way you planned when markets fall.

That completes the course. You’ve seen why a single holding is fragile, how to spread across sectors, sizes and countries, how funds and individual stocks can share the work, and how to hold the mix steady. If income is the goal, the Dividend Income Portfolio course applies the same thinking to a portfolio built for payouts.