By Marco BösingWhat Is Risk of Ruin?
Risk of ruin (RoR) refers to the statistical probability of losing all trading capital. It is one of the most important metrics in risk management and reveals whether a trading approach is viable in the long term -- or whether the trader is on a path that mathematically leads to total loss.
The idea behind it is simple: even a profitable system with positive expectancy can destroy your account if you risk too much per trade. Risk of ruin makes this danger measurable. It answers the question: "How likely am I to lose everything given my current strategy and my current risk per trade?"
I consider risk of ruin the metric every trader should know before placing a single live trade. Not because the calculation is particularly complicated, but because the consequence is so fundamental: survival comes before profitability. Always.
How Does Risk of Ruin Work?
The calculation of risk of ruin is based on three variables:
1. Win rate: What percentage of your trades are winners? With a 50% win rate, you win every other trade.
2. Average risk-reward ratio (RRR): How much do you win on an average winning trade relative to what you lose on an average losing trade? With an RRR of 1:2, you win on average twice what you lose.
3. Risk per trade: What percentage of your capital do you risk per trade? This is the variable with the greatest impact on risk of ruin.
The interplay of these three variables determines your fate as a trader. A system with a 40% win rate and an RRR of 1:3 has positive expectancy (you win in the long run). But whether you actually realize that expectancy depends on whether you survive the interim losing streaks. And that is a question of risk per trade.
Concretely:
- 0.5% risk per trade: With a system that has positive expectancy, risk of ruin is effectively zero. You can endure 20, 30, even 40 consecutive losers and still have enough capital to recover.
- 2% risk per trade: Risk of ruin remains low with a good win rate and positive expectancy, but rises noticeably as your edge weakens. A losing streak of 15-20 trades can reduce your account by 30-40%, which is psychologically extremely taxing.
- 5% or more per trade: Risk of ruin increases dramatically. Even with profitable systems, a normal statistical losing streak can halve your account or worse. And after a 50% drawdown, you need a 100% gain just to get back to break-even.
The exact values always depend on the interplay of all three variables. Blanket percentages without these inputs are misleading. That is why I recommend calculating the risk of ruin for your specific system.
Risk of Ruin in Practice
In my day-to-day work, I encounter risk of ruin in two recurring scenarios:
Scenario 1: The trader with a good strategy and oversized positions. I see this regularly. Someone has developed a solid strategy, makes consistent profits on a demo account or with small positions, and then decides to "go big." They increase their risk per trade to 5-10% because they "can afford it" and want to "grow faster." Then a perfectly normal losing streak of 5-8 trades hits, and suddenly 40-60% of the account is gone. The strategy was never the problem. Position sizing was.
Scenario 2: The trader who doubles down after losses. Instead of maintaining the same position size after a loss (or reducing it), some traders double their next position to "make it back." That is the fastest path to ruin. Your risk of ruin explodes because you are increasing risk at the exact moment you have the least capital.
The core message of risk of ruin can be reduced to one sentence: only those who survive can benefit from positive expectancy over time. A dead trader does not make profits, no matter how good their strategy looks on paper.
For practical implications: if your risk of ruin at your current risk per trade exceeds 1%, reduce your risk. If it exceeds 5%, do not trade live until you have brought it down. The difference between risking 1% and 3% per trade may sound small but can mean the difference between 0% and 30% probability of ruin.
Common Mistakes with Risk of Ruin
Mistake 1: Ignoring risk of ruin because the system is profitable. A positive expectancy does not protect you from ruin. It only tells you that you make money in the long run if you can take an infinite number of trades. But "long run" assumes you survive the short-term pain. That is exactly what the risk of ruin calculation is for.
Mistake 2: Overvaluing win rate. An 80% win rate sounds impressive but is meaningless if the RRR is poor. A trader who wins 4 out of 5 trades but loses four times as much on the one loser has no positive expectancy despite a high win rate. Risk of ruin always looks at the complete picture.
Mistake 3: Applying static calculations to dynamic trading. The risk of ruin formula assumes constant position size, constant win rate, and constant RRR. In practice, all three fluctuate. Traders who double their position size after tilt or revenge trading have a significantly higher real risk of ruin than the theoretical calculation suggests.
FAQ
How do I calculate my risk of ruin?
The simplest risk of ruin formula is: RoR = ((1-Edge)/(1+Edge))^N, where Edge = (Win Rate x Avg. Win) - (Loss Rate x Avg. Loss), and N is the number of "units" of your capital (Capital / Risk per Trade). There are online calculators that handle this for you. For a detailed calculation with concrete examples, see the full article.
What is an acceptable risk of ruin?
Below 1% is good. Below 0.1% is better. Zero is the goal, but mathematically that is only achieved with infinitely small risk per trade. Practically, this means: keep your risk per trade low enough that even an extreme losing streak cannot push your account below 50%. Most professional traders risk 0.5-2% per trade.
Does a daily loss limit help against risk of ruin?
Yes, a daily loss limit is one of the most effective measures for reducing real-world risk of ruin. It prevents a single bad day from doing excessive damage to your account. If you stop trading at 3% daily loss, for example, you cap the worst single day at a manageable loss -- regardless of how many trades you lost that day.
Read the full article: Risk of Ruin Formula