Portfolio Rebalancing: Why It Matters and How Often You Should Actually Do It

You picked an asset allocation — say 80% stocks, 20% bonds — because it matched the risk you were willing to take. Two years later, stocks have run up and your portfolio is quietly sitting at 87/13. You didn't do anything wrong. The market just moved, and now you're carrying more risk than you signed up for. That's the problem rebalancing solves.

What Rebalancing Actually Is

Rebalancing means selling some of what's grown and buying more of what hasn't, to bring your portfolio back to its original target mix. It sounds backwards — you're trimming your winners — but that's the point. It forces a mechanical version of "buy low, sell high" instead of relying on gut feeling.

Without it, your portfolio drifts toward whatever asset class happened to perform best recently. Over enough time, that can leave you far more exposed to a single market crash than you intended.

The Two Basic Approaches

There are two common ways to decide when to rebalance:

• Calendar-based: You rebalance on a fixed schedule — once a year, or every six months — regardless of how far your allocation has drifted.
• Threshold-based: You rebalance only when an asset class drifts past a set percentage from its target, no matter when that happens.

Research on this question has found that threshold-based rebalancing can provide a slight return enhancement, particularly using a 5% absolute threshold from a baseline 60/40 portfolio. In plain terms: checking your allocation periodically and only acting when it's meaningfully off target tends to work at least as well as rebalancing on autopilot every year, and often better, because you're not trading when nothing needs fixing.

The 5% Rule

The simplest threshold approach is the flat 5% rule: if you aim for a 60% allocation to a given asset and you set a 5% threshold, a drift to 65% or 55% would prompt a rebalancing transaction. You leave it alone otherwise.

This matters more than it sounds like it should. A 5% drift in a large equity position can quietly shift a portfolio's risk profile, and in a volatile market that extra exposure may double the portfolio's beta — meaning you're taking on more risk than you realize just by doing nothing.

The 5/25 Rule (for Smaller Holdings)

A flat 5% threshold works fine for a big chunk of your portfolio, like a 60% stock allocation. It doesn't work well for smaller slices — a 5% target allocation to emerging markets, for example, would almost never hit a 5-percentage-point move on its own. That's where the 5/25 rule comes in.

The rule says to rebalance when an asset class drifts more than 5 percentage points in absolute terms, or 25% of its target allocation in relative terms — whichever threshold is smaller. A concrete example makes it clearer: if your asset allocation calls for a 10% allocation to gold, you would rebalance when it hit 12.5% or 7.5%. For a smaller holding, like a 5% position in emerging market stocks, the rebalance points would be 3.75% and 6.25%.

This scales the threshold to the size of the position, so you're not ignoring meaningful drift in your small holdings while also not overreacting to noise in your large ones.

A Simple Example

Asset Class	Target	Current	Drift	Rebalance?
U.S. Stocks	50%	56%	+6 points	Yes (past 5% threshold)
Bonds	30%	27%	-3 points	No
International Stocks	15%	13%	-2 points	No (small position, within 25% relative band)
Cash	5%	4%	-1 point	No

In this case, you'd sell some U.S. stocks and use the proceeds to top up bonds and international stocks back toward their targets.

Where You Rebalance Matters for Taxes

Rebalancing inside a 401(k) or IRA costs you nothing in taxes — trades inside tax-advantaged accounts aren't taxable events. Rebalancing in a regular taxable brokerage account is different: selling winners can trigger capital gains tax, and how long you held the position changes the rate you pay.

If you have both account types, the easiest fix is to do most of your rebalancing inside your retirement accounts first. You can also rebalance by directing new contributions toward whatever is underweight, instead of selling anything — that avoids triggering a taxable event entirely.

How Often Is Enough

For most people with a normal mix of index funds, checking your allocation once or twice a year and applying a 5% (or 5/25) threshold is enough. You don't need software, an app that pings you daily, or a quarterly ritual. The goal isn't precision — it's making sure your portfolio doesn't drift so far from your risk tolerance that a downturn hits harder than you can handle.

If you're not sure whether your current mix still matches your goals, or you've never actually checked, running your numbers through a tool like Grade My Finance's financial grade check is a fast way to see where your overall financial picture — including how your investments line up with your goals — actually stands.

The Bottom Line

Rebalancing isn't about timing the market or chasing better returns. It's about keeping the risk level you chose on purpose from quietly turning into a risk level you never agreed to. Pick a threshold, check your allocation once or twice a year, and only act when the drift is big enough to matter.