How does risk budgeting work in practice for asset allocation?

Risk budgeting flips the traditional approach on its head: instead of deciding 'how much money goes into each asset class,' you decide 'how much risk each asset class is allowed to contribute to the portfolio.' **Key Concept: Marginal Contribution to Total Risk (MCTR)** Each asset class contributes to the portfolio's total risk based on: - Its weight in the portfolio - Its volatility - Its correlation with the rest of the portfolio The formula for each asset's **Absolute Contribution to Total Risk (ACTR):** ACTR_i = w_i × β_i × σ_portfolio Where β_i is the asset's beta relative to the portfolio. **Example: Three-Asset Portfolio** | Asset | Weight | Beta to Portfolio | Portfolio σ = 10% | |---|---|---|---| | US Equities | 50% | 1.3 | ACTR = 0.50 × 1.3 × 10% = 6.5% | | US Bonds | 30% | 0.4 | ACTR = 0.30 × 0.4 × 10% = 1.2% | | Real Estate | 20% | 1.15 | ACTR = 0.20 × 1.15 × 10% = 2.3% | | **Total** | 100% | | **10.0%** | **Interpreting the Risk Budget:** - US Equities consume 6.5% / 10.0% = **65% of the risk budget** despite being only 50% of capital - US Bonds consume only **12% of the risk budget** while holding 30% of capital - Real Estate consumes **23% of the risk budget** at 20% of capital **Active Risk Budgeting:** For portfolios managed against a benchmark, you can also budget *active risk* (tracking error). If you have 3% of active risk budget: - 1.5% might go to equity selection (stock picking) - 0.8% to sector tilts - 0.7% to currency bets **Optimal Risk Budgeting (Equal Marginal Risk):** The optimal allocation is where the ratio of expected excess return to MCTR is equal across all asset classes. If one asset has a higher ratio, you're not being compensated efficiently and should shift capital toward it. **Practical Value:** Risk budgeting prevents the common mistake of thinking a '60/40 portfolio' is well-diversified. In reality, the equity portion often contributes 85–90% of total risk. Risk budgeting makes this transparent and actionable. For more on portfolio construction frameworks, explore our CFA Level III course.