What you will learn
- Risk budgets
- Capacity
- Rebalancing costs
- Capital constraints
Risk budgets
Allocation should follow the portfolio objective and constraints rather than the highest recent return alone. Expected returns and risk estimates are uncertain. A highly optimized weight can be fragile to small input changes.
Capacity
Risk budgets may be expressed through exposure, volatility, scenario loss or another measure. The measure should match the decision and be consistently calculated. A percentage label without a defined denominator is incomplete.
Rebalancing costs
Marginal contribution asks how changing one position changes a chosen portfolio risk measure. It depends on the model and the rest of the portfolio. It is not an immutable property of the instrument in isolation.
Capital constraints
Rebalancing incurs turnover, costs and possibly tax or contractual consequences. A rule should specify triggers and review rather than rebalance every small estimated change automatically. Compare net benefits with a simpler policy.
Worked example
An optimizer assigns almost all capital to one strategy because its estimated mean is slightly higher. Small changes in the sample reverse the ranking, revealing dependence on noisy estimates.
Try it yourself
Propose constraints or a simpler comparison that would expose this fragility without claiming a universal optimal allocation.
Show the worked solution
Compare capped or equal-weight baselines, perturb inputs, include turnover costs and report the range of outcomes. The appropriate constraint depends on objectives; stability analysis informs rather than guarantees a weight choice.
Apply this to your course project
Produce a scenario-based portfolio risk dossier.
Keep the calculation inputs, assumptions and decisions with your work. Practical exercises are self-reviewed; the scored knowledge checks assess the questions shown, not an independent certification of practical competence.