How do portfolio managers determine the optimal currency hedge ratio, and what factors make a full hedge suboptimal?

The optimal currency hedge ratio balances the risk reduction from hedging against the costs and potential return drag. While a 100% hedge eliminates currency volatility, several factors make partial hedging or no hedging preferable in many situations.\n\nFactors Affecting Optimal Hedge Ratio:\n\n1. Currency volatility relative to asset volatility: If currency volatility is small relative to equity volatility, the risk reduction from hedging is minimal but costs are real.\n\n2. Correlation between currency and asset returns: Negative correlation means currency movements naturally offset asset losses (a natural hedge). Hedging removes this beneficial offset.\n\n3. Hedging costs: Forward points (carry cost), bid-ask spreads, and roll costs eat into returns. Emerging market currencies can cost 2-5% annualized to hedge.\n\n4. Mean reversion expectations: Currencies that are significantly undervalued (PPP basis) may appreciate, making hedging costly in expectation.\n\n5. Regret risk: A 100% hedge locks in the current exchange rate. If the foreign currency appreciates substantially, the hedged portfolio underperforms.\n\nWorked Example:\n\nStonegate Asset Management runs a $1.5 billion international equity portfolio:\n\n| Currency | Allocation | Volatility | Corr with Local Equity | Hedge Cost (ann.) |\n|---|---|---|---|---|\n| EUR | 35% ($525M) | 8.5% | -0.15 | 0.3% |\n| JPY | 20% ($300M) | 10.2% | -0.25 | 1.8% |\n| GBP | 15% ($225M) | 7.8% | +0.10 | 0.2% |\n| AUD | 10% ($150M) | 11.5% | +0.35 | 0.8% |\n| EM basket | 20% ($300M) | 14.0% | +0.20 | 3.5% |\n\nOptimal hedge ratios (from mean-variance optimization):\n\n| Currency | Optimal Hedge | Rationale |\n|---|---|---|\n| EUR | 70% | Negative correlation provides natural hedge; moderate cost |\n| JPY | 50% | Strong natural hedge (-0.25 corr) but high cost |\n| GBP | 100% | Positive correlation amplifies risk; cheap to hedge |\n| AUD | 80% | High correlation adds risk; moderate cost |\n| EM basket | 25% | Very expensive to hedge; moderate correlation |\n\nCurrency Overlay Implementation:\n\nThe overlay manager executes forward contracts rolled monthly or quarterly:\n\nEUR hedge: Sell EUR 367.5M forward ($525M x 70%)\nJPY hedge: Sell JPY equivalent of $150M forward ($300M x 50%)\nGBP hedge: Sell GBP 225M forward ($225M x 100%)\nAUD hedge: Sell AUD 120M forward ($150M x 80%)\nEM hedge: Various NDF contracts for $75M ($300M x 25%)\n\nDynamic Adjustments:\n\nSophisticated overlay managers adjust hedge ratios dynamically based on:\n- Carry attractiveness (widen hedge when carry is favorable)\n- Momentum signals (increase hedge on trending depreciation)\n- Valuation (reduce hedge when currency is cheap on PPP basis)\n- Volatility regime (increase hedge during high-vol periods)\n\nStudy currency overlay strategies in our CFA Level III course.