Rebalancing: How Often, How Much, and Why a Rule Beats Instinct

Key takeaways

Rebalancing keeps risk where it was designed to be; without it a 60/40 portfolio drifts to 75/25 or more in a long bull market.
Threshold rules (rebalance when an asset class drifts 5 percentage points or 20% of its target) work better than fixed calendars, and a calendar check with a threshold trigger is the practical combination.
Do it in tax-advantaged accounts first, with new contributions and withdrawals second, and with taxable sales last.
The hardest rebalances, buying stocks in a crash, are the ones that matter most.

A portfolio starts with a target: 60% stocks and 40% bonds, or whatever fits the investor. Markets start changing it immediately. After a strong year for stocks the mix is 65/35; after a decade it can be 80/20. The investor now holds a riskier portfolio than the one they chose, and never decided to. Rebalancing is the practice of putting it back, and the rules for doing it are what separate a portfolio that behaves as designed from one that just drifts.

What rebalancing does, and doesn't do

Rebalancing is mostly risk control. It sells the asset class that's grown past its target and buys the one that's shrunk, restoring the intended risk level. Over long periods this has a modest effect on return, sometimes slightly positive (from buying low and selling high between asset classes that move differently), sometimes slightly negative (from selling the asset with the higher expected return, stocks, to buy bonds). The evidence doesn't support rebalancing as a return booster. It supports it as the thing that keeps a 60/40 portfolio from turning into an 80/20 portfolio at the top of a market.

The behavioral effect is bigger than the mathematical one. A rebalancing rule forces you to buy stocks in March 2020 and sell them in late 2021, which is what an investor should do and the opposite of what most people feel like doing. The rule takes the decision away.

Calendar versus threshold

Calendar rebalancing restores targets on a fixed schedule: quarterly, semiannually, annually. It's simple and it ignores what markets are doing, which is both a virtue and a flaw. Annual rebalancing can leave a portfolio badly drifted for eleven months after a major move.

Threshold rebalancing restores targets whenever an asset class drifts outside a band: commonly 5 percentage points in absolute terms (a 40% bond target rebalanced at 35% or 45%), or 20% to 25% of the target in relative terms (a 10% small-cap allocation rebalanced at 8% or 12%). Research from Vanguard and others finds that threshold approaches control risk with fewer trades than frequent calendar rebalancing.

The combination, which is what we use: check on a schedule, monthly or quarterly, and trade only when a threshold is breached. Most checks produce nothing. A major market move produces a trade promptly.

Where to rebalance

The order matters for tax.

Tax-advantaged accounts first. Trades inside an IRA, 401(k), or Roth have no tax cost. Because asset location puts bonds mostly in the IRA and stocks mostly in taxable accounts, a large share of rebalancing can happen inside the IRA by shifting between its holdings.
New money and withdrawals second. Send contributions to the underweight asset class and take withdrawals from the overweight one. For a retiree drawing $8,000 a month, this alone rebalances gradually all year.
Dividends and distributions. Turn off reinvestment in taxable accounts and point the cash where it's needed.
Taxable sales last, and when you have to, sell the highest-basis lots and pair sales with harvested losses where possible.

Rebalancing inside asset classes

The same logic applies within stocks: U.S. versus international, large versus small, market versus value tilt. A factor tilt that has trailed for three years will have shrunk below its target, and rebalancing buys more of it right when its expected premium is highest. This is where discipline gets tested, because rebalancing into the thing that's been losing feels wrong every single time.

The hard rebalance

In a sharp decline, a 60/40 portfolio can become 50/50 in weeks. The rule says sell bonds and buy stocks. Doing that in March 2020 or October 2008 was the single most valuable trade of those years, and it was the one nobody wanted to make. A written policy, a threshold that's already been breached, and an advisor whose job is to execute the rule are what make it actually happen. This is also where a bond allocation sized to the household's spending earns its keep: there are enough bonds to fund the withdrawals and the rebalance at the same time. See sequence of returns risk.

What not to do

Rebalance every month with taxable sales, which generates tax and trading costs for no benefit. Skip rebalancing in a bull market because "stocks are doing well," which is how a retiree ends up 85% in stocks the year before a crash. Rebalance based on a forecast instead of a rule. Or set the target once and never revisit it. The allocation itself should change as the investor's horizon and needs change, and the rebalancing rule serves the current target, not the original one.

How we do it

Every client portfolio has a written target allocation, bands of five points on the stock share and a quarter of each holding's own target, a monthly check, and a location-aware trade order. Rebalancing trades get combined with tax-loss harvesting, with the year's withdrawal plan, and with contributions, so most rebalancing happens without a taxable sale. It's unglamorous. It's also most of what investment management is on a month-to-month basis, and it's the part that keeps the portfolio the client agreed to from quietly becoming a different one.

Frequently asked questions

How often should I rebalance my 401(k)?

Most plans offer automatic rebalancing on a schedule; quarterly or semiannual is reasonable, and there's no tax cost inside the plan. Set it and let it run.

Should I rebalance if the market is falling?

Yes, by the rule. Buying stocks after a decline is the whole point. Whether to do it all at once or in stages is a matter of preference; the rule is the same.

Does rebalancing trigger the wash sale rule?

Only if you sell a position at a loss and buy it back within 30 days. Rebalancing sales in a decline are usually paired with a replacement fund, as in tax-loss harvesting.

What if my target allocation is wrong?

Then change the target, not the rule. The allocation should be revisited when your situation changes: retirement, a windfall, a change in spending needs. Between those events, the rule holds it in place.

Joseph G. Valerio, CFP®, EAFounder and Lead Advisor at Valerio Wealth Management, a fee-only, fiduciary virtual family office in Miami, Florida. One advisor, credentialed in both financial planning and federal tax. About Joseph

This article is general education, not individualized advice, and it is not tax, legal, or accounting advice. Figures reflect federal law for the year stated and can change. Valerio Wealth Management does not prepare or file tax returns. Speak with a qualified professional about your own situation before acting.