Direct Answer
The Ulcer Index is a volatility measure developed by Peter Martin that focuses specifically on downside risk, the depth and duration of drawdowns from recent highs, rather than overall price fluctuation. Unlike standard deviation, which treats a sharp rally and a sharp decline as equally "volatile," the Ulcer Index stays low while a security is making new highs and rises only when price is sitting below a prior peak.
Key Takeaways
- The Ulcer Index only measures how far and how long price has fallen below a prior high over the lookback window, it ignores upside volatility entirely.
- Squaring each period's percentage drawdown before averaging means deep drawdowns dominate the reading far more than several shallow ones.
- A 14-period lookback is the commonly cited default, but always verify the setting on your specific platform before comparing readings across tools.
What Is the Ulcer Index?
The Ulcer Index is a volatility measure developed by Peter Martin that focuses specifically on downside risk, the depth and duration of drawdowns from recent highs, rather than overall price fluctuation. Unlike standard deviation, which treats a sharp rally and a sharp decline as equally "volatile," the Ulcer Index stays low while a security is making new highs and rises only when price is sitting below a prior peak. The name comes from the discomfort ("ulcer") an investor is presumed to feel while watching an account sit in a drawdown.
The Formula
Percentage Drawdowni = 100 × (Closei − MaxClose(prior n periods including i)) / MaxClose(prior n periods including i)
This value is zero when the current close is at or above the highest close in the lookback window, and negative whenever price is below that recent high.
Ulcer Index = square root of the average of Percentage Drawdowni squared, over the lookback window (commonly 14 periods).
Squaring each period's percentage drawdown before averaging means larger drawdowns are weighted more heavily than several small ones. Because the index only measures distance below a running high, never distance above it, it rises during sustained losses and stays flat during rallies, which is the core distinction from a symmetric measure like standard deviation.
Worked Example
Hypothetical example, for education only.
Consider a simplified 5-day close series (a real calculation commonly uses a 14-period window; this shorter window is used here only to keep the arithmetic visible): $100, $98, $95, $97, $94.
| Day | Close | MaxClose (prior periods incl. today) | % Drawdown |
|---|---|---|---|
| 1 | $100.00 | $100.00 | 0.0% |
| 2 | $98.00 | $100.00 | −2.0% |
| 3 | $95.00 | $100.00 | −5.0% |
| 4 | $97.00 | $100.00 | −3.0% |
| 5 | $94.00 | $100.00 | −6.0% |
Squaring each percentage drawdown gives 0, 4, 25, 9, and 36. Averaging those squares: (0 + 4 + 25 + 9 + 36) / 5 = 14.8.
Ulcer Index = square root of 14.8 ≈ 3.85.
Over this window, the security spent every day but the first below its running high, closing as much as 6% under that high, the Ulcer Index of roughly 3.85 reflects both the depth and the persistence of that drawdown, not the day-to-day size of each price move.
How the Ulcer Index Is Used
Comparing downside risk across securities
Two securities can show similar standard deviation while one spends most of its time near new highs and the other lingers in deep drawdowns, the Ulcer Index is commonly used to separate those cases when comparing candidates by downside risk rather than overall price swing.
Risk-adjusted return
The Ulcer Index is the volatility term behind the related Ulcer Performance Index, which divides a return figure by the Ulcer Index instead of by standard deviation, a way to reward strategies that avoid deep, prolonged drawdowns rather than just avoiding day-to-day noise.
Reading the trend of the line
A rising Ulcer Index indicates the current drawdown is deepening or persisting; a falling Ulcer Index indicates price is recovering toward (or making) new highs. As with any single indicator. This is commonly read alongside price structure and other risk measures rather than in isolation.
Common Lookback Periods
| Lookback (periods) | Responsiveness | Common use |
|---|---|---|
| 10 | Faster, more reactive to recent drawdowns | Shorter-term risk monitoring |
| 14 | Balanced (commonly cited default) | General-purpose downside-risk analysis |
| 21 | Slower, smoother | Longer-term or portfolio-level risk review |
The 14-period default is a commonly cited convention, not a fixed rule, verify the default lookback on your specific charting platform before comparing readings across tools, since some allow the period to be changed while others fix it.
Limitations
- Backward-looking by construction, the MaxClose term is calculated from prior closes, so the index reports a drawdown that has already occurred rather than forecasting one.
- Ignores upside volatility entirely, a security that swings violently but stays near new highs will show a low Ulcer Index, which is useful for isolating downside risk but means it should not be read as a complete volatility picture on its own.
- Sensitive to the chosen lookback window, a short window can understate a drawdown that started before the window began; a long window can smooth over a sharp, recent decline.
Common Mistakes
- Treating the Ulcer Index as a replacement for standard deviation, they answer different questions; standard deviation captures total variability, the Ulcer Index captures only sustained downside.
- Comparing Ulcer Index readings across platforms without checking the lookback setting, a shorter or longer window than the 14-period default will produce a different reading for the same price series.
- Reading a single Ulcer Index value in isolation, the trend of the line (rising vs. falling) over time is generally more informative than one static reading.
Measuring Only the Part of Volatility That Hurts
The Ulcer Index measures the depth and duration of declines from previous highs, ignoring upside movement entirely. That asymmetry is deliberate and it addresses a real complaint about standard volatility measures, which penalise a sharp advance exactly as much as a sharp decline.
The practical use is in comparing investments that have similar returns. Two assets with the same total return and very different Ulcer readings offered very different experiences to hold, and the one with the lower reading spent less time underwater. For anyone whose behaviour deteriorates during drawdowns, that is the more relevant number.
The mistake is reading it as an absolute scale. The value has no natural units and depends on the period, the frequency of the data and the length of the history examined, so it is meaningful in comparison between series measured identically and meaningless as a standalone figure.
The measure also describes what has already happened. A low reading over a favourable stretch reflects that stretch, and an asset that has not yet experienced a difficult period will show a comfortable figure until it does.
Ulcer Index FAQs
What is the Ulcer Index?
The Ulcer Index is a volatility measure developed by Peter Martin that focuses on downside risk, the depth and duration of drawdowns, rather than overall price fluctuation in either direction.
How is the Ulcer Index calculated?
First, a percentage drawdown is calculated for each period as 100 times the close minus the highest close over the prior lookback window (including the current period), divided by that highest close. The Ulcer Index is then the square root of the average of those percentage drawdowns squared, over the lookback window.
What lookback period does the Ulcer Index use?
A 14-period lookback is the most commonly cited default, though this is a heuristic rather than a fixed rule, shorter windows react faster to recent drawdowns, longer windows smooth the reading. Always verify the default your specific charting platform uses.
How is the Ulcer Index different from standard deviation?
Standard deviation treats upside and downside price moves symmetrically, so a sharp rally raises it just as much as a sharp decline. The Ulcer Index only measures distance below a prior high, so it rises during sustained losses and stays low or flat while a security is making new highs, even if those gains are volatile.
What does a high Ulcer Index mean?
A higher Ulcer Index reading indicates deeper and/or more prolonged drawdowns relative to recent highs over the lookback window. Because the percentage drawdowns are squared before averaging, large drawdowns dominate the reading more than several smaller ones.
Who created the Ulcer Index?
The Ulcer Index was developed by Peter Martin, who also co-created the related Ulcer Performance Index, which adjusts return by this downside-focused volatility measure instead of standard deviation.
Why does the index only consider downside movement?
It is built from the depth of declines below prior peaks, so upward movement contributes nothing. This reflects a view that upside variability is not what investors experience as risk. It makes the measure asymmetric by design, which is the main conceptual difference from standard deviation and the reason two portfolios with identical standard deviations can produce very different readings.
How should the index be compared between two investments?
Both must be computed over the same period and with the same lookback, since the reading depends on which declines fall inside the window. Comparisons are meaningful in relative terms rather than against any absolute threshold, because the scale has no natural interpretation. A lower reading indicates shallower and shorter declines over that specific period.
Does the index work for instruments held for short periods?
It is constructed around drawdowns from peaks, which needs enough history for meaningful peaks and recoveries to exist. Applied to a short window it reduces to a description of whatever decline happened to occur, with little to distinguish signal from a single event. It is better suited to evaluating investments over months and years than to short-term analysis.
References
- CMT Association: Technical Analysis Body of Knowledge and Research
- CFA Institute Research and Policy Center: Investment Research
- TA-Lib: Technical Analysis Function Library Documentation
- Peter Martin developed the Ulcer Index, along with the related Ulcer Performance Index, as a downside-focused alternative to standard deviation for measuring investment risk.
- SEC Investor.gov: Introduction to Investing