How to calculate Expected Shortfall
Worked example
- Portfolio $100,000, mean daily return 0.05%, daily volatility 1.2%, 95% confidence.
- φ(1.645) = 0.1031, so ES = 1.2% × 0.1031 ÷ 0.05 − 0.05% = 2.425%.
- In money: $2,425 — the average loss on the worst 5% of days, versus a VaR of $1,924.
How to interpret Expected Shortfall
ES answers the question VaR avoids: “when it goes badly, how badly?”. For normally distributed returns, 95% ES is about 1.25× VaR; a much larger ratio in historical data signals fat tails. Compare both on the VaR calculator.
Limitations and common mistakes
- Historical ES at 99% needs a lot of data — with 250 daily returns, only 2–3 observations sit in the tail.
- ES is always larger than VaR at the same confidence level.