Two backtests can share the same maximum drawdown and still put a prop account through very different ordeals. Ulcer Index exposes the difference by measuring every percentage drawdown from the running equity peak, not only the single worst fall.
That makes it useful for judging depth and persistence together. It does not predict the next drawdown, and it does not replace the account's hard loss rules.
What Ulcer Index measures
Ulcer Index is the root mean square of percentage drawdowns from prior equity peaks. A new high contributes zero; every underwater observation contributes its squared distance below the running peak.
The calculation is:
drawdown(t) = 100 × (equity(t) - running peak(t)) / running peak(t)
Ulcer Index = square root of [sum of drawdown(t)² / N]Squaring does two jobs. It makes negative drawdowns positive for the calculation, and it gives deeper drawdowns more weight than shallow ones. Persistence enters because a curve that remains underwater keeps adding non-zero observations.
Peter Martin's original Ulcer Index explainer describes the measure as the depth and duration of drawdowns from earlier highs. That wording matters: this is a path metric, not another name for volatility.
The same max drawdown can hide two different paths
Maximum drawdown records one worst peak-to-trough percentage. It cannot tell whether the curve recovered immediately or stayed below its peak through most of the test.
Consider two simplified equity paths sampled at the same frequency:
| Observation | Path A | Path B |
|---|---|---|
| Start | 100 | 100 |
| Next | 96 | 92 |
| Next | 92 | 100 |
| Next | 94 | 100 |
| Next | 98 | 100 |
| End | 100 | 100 |
Both paths have an 8% maximum drawdown. Their underwater experiences are not alike.
Path A has drawdowns of 0%, -4%, -8%, -6%, -2%, 0%. Its Ulcer Index is:
square root of [(0² + 4² + 8² + 6² + 2² + 0²) / 6] = 4.47%Path B has drawdowns of 0%, -8%, 0%, 0%, 0%, 0%. Its Ulcer Index is:
square root of [(0² + 8² + 0² + 0² + 0² + 0²) / 6] = 3.27%The worst historical drop is identical. Path A scores worse because the equity remains below its peak across more observations. That is the information max drawdown discards.
Why Ulcer Index matters to a prop trader
Ulcer Index helps a prop trader distinguish a brief loss shock from an equity curve that repeatedly or persistently sits below its high-water mark. Both can post the same return and max drawdown; the second path usually leaves less room for ordinary variance before a loss rule becomes the real constraint.
The metric is most useful in three comparisons:
| Comparison | What a lower Ulcer Index can indicate |
|---|---|
| Same strategy, different settings | Less deep or less persistent underwater equity |
| Two strategies over the same window | A calmer drawdown path, after keeping sizing and data frequency comparable |
| Portfolio before and after adding a strategy | Whether diversification actually improved the combined equity path |
The word can is doing honest work. A low historical Ulcer Index is evidence about the tested path, not a ceiling on the next one.
Prop rules still take priority. The current firm's definition of daily loss, total loss, balance, and floating equity decides whether an account passes. The funding page explains the prop-account context; the firm's current rules remain the final reference.
How to calculate it without flattering the backtest
Ulcer Index is only as honest as the equity series underneath it. A clean calculation on a distorted backtest is still a distorted answer.
Use this review:
- Build the series from equity, not balance, when floating loss is relevant to the account rule.
- Deduct spread, slippage, commission, and swap before calculating the path.
- Keep the start date, end date, sizing method, and sampling frequency identical when comparing systems.
- Calculate in-sample and out-of-sample segments separately as well as across the full test.
- Inspect the underwater chart beside the final number.
Sampling frequency deserves special attention. Daily closes can miss an intraday equity breach that a prop firm would count. Tick data can produce a more detailed series, but it can also make comparisons unwieldy. The practical answer is to preserve the resolution relevant to the rule and apply it consistently.
At realbacktesting, the published methodology uses cTrader-native testing with intrabar M1 execution, trading costs, and an out-of-sample hold-out. Those choices matter here because an underwater metric cannot recover excursions the underlying test failed to record.
What Ulcer Index does not tell you
Ulcer Index does not tell you whether a strategy has positive expectancy, whether a loss limit was breached, or whether the result will persist out-of-sample. It compresses one part of the historical path into one number.
It also has comparison traps:
- A shorter test may simply contain fewer difficult regimes.
- A different sampling interval changes how many underwater observations enter the average.
- Higher leverage worsens the equity path even when the entry logic is unchanged.
- One low score can hide a recent deterioration, so the underwater chart still matters.
- A strategy can have a low Ulcer Index and weak returns; smooth stagnation is still stagnation.
This is why the metric belongs beside maximum drawdown, drawdown duration, expectancy, and rule-breach checks. It is a diagnostic, not a ranking machine.
For another view of path risk inside individual trades, see maximum adverse excursion for prop traders. For downside deviation rather than peak-relative drawdown, see what Sortino misses in prop backtests.
Frequently asked
Is Ulcer Index better than maximum drawdown?
Ulcer Index is not universally better; it answers a wider path question. Maximum drawdown shows the worst historical fall, while Ulcer Index reflects the depth and persistence of all drawdowns in the chosen series.
Is a lower Ulcer Index always better?
A lower Ulcer Index means the tested curve spent less time or less depth below its peaks, under the same calculation choices. It says nothing by itself about return, expectancy, future risk, or compliance with a prop firm's loss rules.
Should Ulcer Index use balance or equity?
Use equity when floating profit and loss affects the rule being studied. A balance-only series can hide open losses that existed before trades closed.
Is Ulcer Index the same as the Martin ratio?
No. Ulcer Index is the drawdown-risk denominator. The Martin ratio, also called the Ulcer Performance Index, divides excess return by Ulcer Index.
The stubborn takeaway
If a backtest reports only its deepest drawdown, it tells you how low the floor became. Ulcer Index tells you how much of the test was spent trying to climb back out.