Asset Allocation and Rebalancing: Keep Risk From Drifting by Accident

Asset allocation is the portfolio's risk structure

Asset allocation describes how a portfolio is divided among broad asset categories such as stocks, bonds and cash. Diversification describes how broadly risk is spread both between asset classes and within them.

Neither concept guarantees against loss. They are ways to structure risk around a goal and time horizon.

Why portfolios drift

Suppose you choose a 60% stock / 40% bond target. After a strong stock market, the portfolio becomes 72% stock / 28% bonds even though you never placed a trade.

Your portfolio now has more equity exposure than you originally chose. If the target reflected the amount of volatility you could tolerate, doing nothing has quietly changed the risk decision.

Rebalancing means moving the portfolio back toward the intended allocation.

Worked example

Start with $100,000:

• $60,000 stocks
• $40,000 bonds

After market moves, stocks rise to $78,000 while bonds are $42,000. Total portfolio = $120,000.

The portfolio is now 65% stocks and 35% bonds. A 60/40 target would imply $72,000 stocks and $48,000 bonds.

One way to rebalance would be selling $6,000 of stocks and buying $6,000 of bonds. But that is not the only way.

If you are contributing new money, you could direct the next contributions toward bonds until the portfolio moves closer to target. In a taxable account, that may reduce the need to realize gains solely to rebalance.

Calendar vs threshold rebalancing

Two common frameworks are:

Calendar review: Check the allocation at a regular interval, such as every six or twelve months.

Threshold review: Rebalance when an asset class moves far enough away from its chosen target.

There is no universal magic interval. The point is to use a rule that prevents every market headline from becoming a portfolio decision.

What should change the target allocation?

A target can reasonably change when the underlying plan changes—for example:

• the goal gets closer;
• your capacity to absorb losses changes;
• a major cash need appears;
• retirement date changes;
• the purpose of the account changes.

A recent rally or selloff by itself is different. Increasing stock exposure because stocks just rose strongly can turn rebalancing into performance chasing.

Diversification is more than owning several funds

Owning five ETFs does not automatically mean you are diversified. If all five are dominated by the same large technology companies, the portfolio may have substantial overlap.

Look through the wrappers to understand:

• major asset classes;
• geographic exposure;
• sectors;
• concentration in individual securities;
• duration and credit risk for bonds;
• overlap among funds.

Taxes and transaction costs matter

Selling appreciated positions in a taxable account can realize capital gains. Trading can also create spreads or other transaction costs. Before rebalancing, consider whether contributions, dividends or withdrawals can do some of the work.

Inside a tax-advantaged account, current capital-gain taxation generally does not work the same way, which can make rebalancing mechanically simpler.

Common mistakes

1. Changing the target because the market moved.
2. Calling several overlapping funds diversified.
3. Rebalancing too frequently without a reason.
4. Ignoring taxes in taxable accounts.
5. Setting a target without connecting it to a specific goal.
6. Using an allocation questionnaire as a substitute for understanding the downside.

A practical annual review

Ask:

• What is this portfolio for?
• When will the money be needed?
• What loss could I tolerate without abandoning the plan?
• What is the current allocation?
• How far has it drifted from the intended target?
• Can new contributions reduce the drift?
• Would selling create a tax consequence?
• Has my financial situation actually changed?

Rebalancing is not about predicting what wins next. It is about keeping the portfolio's risk aligned with the decision you already made.