BA-303 · Lesson 9 of 9

Building and Rebalancing a Portfolio

You draft an investment policy, compare rebalancing rules and learn to avoid behavioral mistakes.

15 min read Advanced Portfolio Management
Track contents Financial Analysis for Investors
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The investment policy

  1. Define your objectivesWhat you want to achieve (capital growth, regular income, capital preservation) and by when.
  2. Assess your constraintsLiquidity needs, horizon, tax considerations, knowledge and experience, personal preferences.
  3. Set the target allocationWeights by asset class, consistent with your risk profile — for example, 60% equities and 40% bonds.
  4. Set limits and rulesTolerance bands, maximum weights per issuer, review frequency and rebalancing method.
  5. Implement and monitorSelect the instruments, track results against your objectives and revise the policy only when your circumstances genuinely change.

Why and how to rebalance

Different returns across asset classes shift the portfolio's weights over time. After a period of rising equity prices, the portfolio becomes riskier than originally intended. Rebalancing brings the weights back to target and maintains the chosen risk profile; its main purpose is not to maximize returns.

Current weight and deviation from target
Current weight = Value of the asset class ÷ Total portfolio value × 100%; Amount to trade = Current value − Target weight × Total value
A positive amount means selling from that asset class; a negative amount means buying.
CriterionPeriodic rebalancingThreshold rebalancing
TriggerAt fixed intervals (for example, annually)When a weight moves outside its tolerance band (for example, ±5 percentage points)
AdvantagesSimple, predictable, easy to followTrades only when the deviation is significant
DisadvantagesCan generate unnecessary trades or miss large deviations between datesRequires continuous monitoring
CostsMay be incurred at every date, regardless of the deviationGenerally fewer trades

A numerical rebalancing example

The rule you choose matters: with annual rebalancing, the trade above is executed. With a tolerance band of ±5 percentage points (55%–65%), the 64.10% weight is still inside the band, so nothing is traded. An alternative that avoids selling is to direct new contributions: if the investor adds MDL 50,000 to bonds only, bonds reach MDL 470,000, the total reaches MDL 1,220,000 and the equity weight falls to 750,000 ÷ 1,220,000 ≈ 61.48%.

Discipline and behavioral mistakes

By its nature, rebalancing requires you to sell what has gone up and buy what has gone down — exactly the opposite of your emotional impulse. That is why a rule set in advance is more valuable than a decision made under market pressure.

  • Loss aversion: losses are felt more strongly than equivalent gains, which leads to panic selling.
  • The disposition effect: the tendency to sell winning securities too early and hold on to losing ones for too long.
  • Overconfidence: overestimating your own ability to predict the market, leading to excessive trading.
  • Herd behavior: following the decisions of the majority instead of your own analysis.
  • Anchoring: basing decisions on an irrelevant reference price, such as the purchase price.

Key takeaways

  • A written investment policy sets out objectives, the target allocation, limits and rules before you invest.
  • Rebalancing brings the portfolio back to the chosen risk profile; its main purpose is risk control.
  • Periodic rebalancing is simple, while threshold rebalancing trades only when deviations are significant.
  • Trading costs and taxes influence the optimal rebalancing frequency.
  • Rules set in advance help you avoid behavioral mistakes.

Check your knowledge

Answer all the questions. If you answer all of them correctly, the lesson is marked as completed automatically.

Question 1 of 3An MDL 1,170,000 portfolio holds MDL 750,000 in equities, and the equity target is 60%. How much equity must be sold to return to target?

Explanation: Target = 0.60 × 1,170,000 = MDL 702,000; amount to sell: 750,000 − 702,000 = MDL 48,000.

Question 2 of 3The equity target is 60%, with a tolerance band of ±5 percentage points. The current weight is 64.10%. What does the threshold rule require?

Explanation: The threshold rule triggers rebalancing only when the weight moves outside the band; 64.10% is below the 65% limit.

Question 3 of 3What is the main purpose of rebalancing?

Explanation: Rebalancing brings the weights back to the target allocation, preserving the chosen level of risk; it is not a tool for predicting the market.

Finished the lesson?Mark it as completed to track your progress.

Educational material only. It does not constitute investment, legal or tax advice. Numerical examples are hypothetical.