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How to Measure Portfolio Risk: Standard Deviation, Max Drawdown and the Sharpe Ratio
Key takeaways
- Standard deviation measures the average fluctuation of returns around the mean — the higher it is, the more volatile the fund.
- Max drawdown shows the largest historical decline from peak to trough — the most psychologically painful number for an investor.
- The Sharpe ratio compares return with risk taken — a fund with a higher Sharpe ratio earns more efficiently per unit of risk.
- No single metric is sufficient: a high Sharpe ratio can mask tail risks (fat tails).
- These metrics are historical — future risk can be different, especially in unprecedented crises.
Portfolio risk can be translated into concrete numbers — the three most widely used metrics are the standard deviation of returns, maximum drawdown and the Sharpe ratio. Each says something different and all of them have blind spots.
Standard deviation: the basic measure of volatility
The standard deviation of returns tells you by how much the typical annual return differs from the long-run average. If a fund has an average return of 8% and a standard deviation of 15%, in a "normal" year the return is roughly between -7% and +23%. A higher standard deviation means a wider spread of outcomes — a greater chance of a substantial gain and a substantial loss. See also volatility vs. risk.
Maximum drawdown: the hardest test of nerve
Max drawdown (MDD) is the largest historical decline of a portfolio from peak to trough. If a portfolio reached a value of 100, then fell to 60 and then recovered, the MDD is 40%. It is a practical metric: it tells you what you had to endure at the worst moment before the portfolio recovered. The longer the recovery took, the more psychologically demanding. Find your fund's MDD and ask yourself: "Could I have held on without selling?"
- The global equity index lost over 50% from peak to trough in 2008–2009
- Recovery to pre-crisis levels took approximately 4–5 years
- The investor who held on was rewarded; the investor who sold in panic locked in a loss
Sharpe ratio: the efficiency of return
The Sharpe ratio compares the return achieved with the degree of risk taken (standard deviation). A fund with a return of 10% and a standard deviation of 20% has a lower Sharpe ratio than a fund with a return of 8% and a standard deviation of 8%. It says: "For each unit of risk, how much return did I receive?" A higher Sharpe ratio is better — but note: the metric ignores tail risks (extremes that occur rarely but destructively).
The limits of historical metrics
All metrics are backward-looking — they measure the past. A crisis without precedent (global pandemic, geopolitical shock) will not show up in a historical MDD in advance. That is why investors combine quantitative metrics with qualitative assessment: what would have to happen for this investment to permanently lose value? We discuss how to think more deeply about portfolio risk in what is risk and how to measure it at all. For practical steps in a review see semi-annual portfolio review.
FAQ
What is max drawdown?
Max drawdown is the largest historical decline of a portfolio or fund from peak to trough. It tells you what you had to endure at the worst moment. The higher the number, the stronger the nerves required — or the more conservative the allocation you need.
What is the Sharpe ratio?
The Sharpe ratio compares a fund's return with the degree of risk (volatility) taken. The higher it is, the more efficiently the fund earned per unit of risk. Good for comparing funds with a similar strategy — not suitable for comparing across completely different asset classes.
Is one metric sufficient for assessing risk?
No. Standard deviation describes typical fluctuations, MDD captures the worst-case scenario, the Sharpe ratio evaluates efficiency. Together they give a better picture — but no historical metric will capture a future crisis that has no precedent.