Rebalancing

Rebalancing is the practice of returning a portfolio to its target weights after the market moves them. A 60/40 split of stocks and bonds drifts whenever one side outperforms, and two strong equity years can turn it into 70/30 without a single trade. Restoring the weights means trimming the winner and adding to the laggard, which is mechanically selling high and buying low whether the investor feels like it or not.

The standard cadences are a calendar — annually is common — or threshold bands, typically 5 points of drift, whichever arrives first. Inside a 401(k) or IRA the trades are free of tax; in a taxable account selling winners realizes gains, so most plans direct new contributions to the lagging asset instead. Vanguard's research finds rebalancing adds little to returns and a great deal to risk control, which is the point.

The arithmetic is one restoration. Start with $100,000 at 60/40: $60,000 of stocks, $40,000 of bonds. A year in which stocks gain 25% and bonds sit flat leaves $75,000 and $40,000, a $115,000 portfolio that is 65% equity. Restoring 60/40 means selling $6,000 of stocks and buying $6,000 of bonds, which books a profit on exactly the assets that outran the plan.

The cadence is a choice between two triggers. A calendar rebalance runs once or twice a year and requires no monitoring; a band rebalance acts only when a sleeve drifts 5 or more points from target, trading less often through quiet markets. Both work; the failure mode is neither, which is the portfolio that drifts for a decade because checking felt optional. Target-date funds run this machinery internally every day, which is part of what their 0.4% average fee buys.

The tax location decides the cost. Inside a 401(k), IRA, or Roth, rebalancing trades carry no tax bill, so bands and calendars run free. In a taxable account, selling an overweight winner realizes capital gains, so the standard move is cash-flow rebalancing: aim each new contribution and every dividend at the lagging sleeve until the weights restore themselves. It is slower, and it is free.

Drift is a risk decision made by the market instead of by the investor. A 60/40 portfolio left alone through a bull market arrived at 69/31 by the peak, which is a third more equity risk than the plan specified, right before the year that tests it. Rebalancing is the scheduled meeting where the investor, not the market, rewrites the risk budget.

I watched a colleague named Brent (yes, that Brent) inherit a tidy 60/40 portfolio and never once look at the weights. Five fat years later it was 85/15 and he described it as aggressive, which by then was flattery. The 2022 rebalance he finally attempted — selling bonds, the side that had fallen — was the one move the discipline explicitly forbids.

The highest-leverage thing most Americans can do is write down target weights, check them once a year, and rebalance inside retirement accounts where the tax man is not a counterparty. Check the drift with the portfolio rebalancing calculator and reset the mix with the asset allocation calculator. The written weights are the plan; the calendar is the enforcement.