Risk of Ruin

Risk of ruin is the probability that a strategy, at the position size you trade it, loses enough of your account that you can no longer keep going. "Ruin" does not have to mean a zero balance. For most traders it is the drawdown that ends the plan in practice: the point where the account is too small to trade properly, a funded account hits its loss limit, or you lose the nerve to take the next setup.

The idea matters because trading is a long series of bets, and an edge only shows up across many of them. A strategy with a genuine positive expectancy can still go broke if it is sized so that an ordinary bad run wipes out the account first. Risk of ruin is the number that tells you whether you will still be around for the average to arrive.

The Classic Risk of Ruin Formula

The textbook version comes from the gambler's ruin problem in probability. Picture a game where every bet wins or loses the same fixed amount, you win with probability p, you lose with probability q = 1 − p, and your account holds N of those betting units. If p is greater than q, the chance of eventually losing every unit is:

Risk of ruin = (q ÷ p)^N

If p is 50% or less, ruin is eventually certain, however much money you start with. (Gambler's ruin, Wikipedia)

Two lessons survive from this simple model. First, with no edge, size cannot save you, only delay the end. Second, with an edge, the number of units you hold, which is really the inverse of how much you risk per bet, drives ruin down exponentially. Going from 10 units to 20 does not halve the risk. At a 55% win rate it cuts it from about 13% to under 2%.

Why the Simple Formula Is Not Enough for Trading

Real trading breaks the assumptions behind (q ÷ p)^N in three ways:

• Wins and losses are not the same size. A strategy that wins 40% of the time with winners twice the size of its losers has a positive expectancy, but the even-payoff formula would treat it as a losing game.
• Most traders do not bet fixed units. Risking a fixed percentage of current equity means size shrinks after losses, so the balance never technically reaches zero. Ruin has to be defined as a drawdown threshold instead.
• There is a time horizon. You care about what happens over the next few hundred or thousand trades, not forever.

So the practical approach is to simulate. Feed in your win rate, your average win and loss in R-multiples, your risk per trade and a horizon, run thousands of possible trade sequences, and count how many hit your ruin line.

How Risk Per Trade Drives Risk of Ruin

Here is that simulation for one strategy with a real edge: a 40% win rate, winners of 2R, losers of 1R, for an expectancy of +0.2R per trade. Each run is 1,000 trades sized as a fixed percentage of current equity, and the chart counts how often the account suffers a 30% or a 50% peak-to-trough drawdown along the way, across 20,000 runs.

Nothing about the strategy changes from row to row. Same win rate, same payoffs, same expectancy. Only the risk per trade moves, and the chance of halving the account goes from negligible to near certain within a span of about three percentage points. The curve is steep, which is why "a bit more size" is rarely the small change it feels like.

The same simulation with no edge at all (a 50% win rate and 1:1 payoffs) shows the other side. At 1% risk, about 7% of runs hit a 50% drawdown within 1,000 trades. At 2% risk, about 62% do. Small size buys time. It does not turn a losing game into a winning one.

What Moves Risk of Ruin

The inputs that describe the strategy (win rate and payoff) are hard to change quickly and uncertain to estimate. Risk per trade is the one you choose fresh on every trade, which makes it the main control you have.

Using Risk of Ruin in Practice

1. Define your own ruin. Pick the drawdown that would actually end things: the point where you would stop trading the plan, or an account rule you cannot break. For many traders that is somewhere between 20% and 50%, and it is lower than they first guess.
2. Take honest inputs from your record. Use your real win rate and average win and loss in R over a meaningful sample, not your best month or a backtest you have not traded. Be conservative, because small samples overstate edges.
3. Simulate, or use a calculator, across a realistic horizon. A year of your normal trade count is a sensible starting point.
4. Size so the answer is small. If the chance of hitting your ruin line is more than a few percent, reduce risk per trade until it is not.
5. Re-run it when the inputs change. A new setup, a market regime where your win rate drops, or a jump in trade frequency all change the answer.

One related idea is the Kelly criterion, which calculates the bet size that maximizes long-run growth for a given edge. For the strategy above it works out to 10% per trade, a size at which a 50% drawdown within 1,000 trades is a near certainty. Growth-optimal and survivable are not the same thing.

Key Takeaways

• Risk of ruin is the chance a strategy loses enough to stop you trading it before its edge plays out.
• The classic formula, (q ÷ p)^N, shows that with no edge ruin is certain, and with an edge it falls exponentially as risk per bet shrinks.
• For real trading, define ruin as a drawdown you could not sit through and estimate it by simulation from your own win rate and payoffs.
• In the example above, the same profitable strategy goes from a 5% chance of a 50% drawdown at 2% risk to 82% at 4% risk.
• Risk per trade is the input you control on every trade, so it is the main way to keep risk of ruin small.

Common Mistakes

Assuming a positive expectancy means you are safe. Expectancy describes the average. Ruin happens in the variation around it, during streaks that a profitable strategy will still produce.

Defining ruin as zero. Almost nobody trades an account down to nothing. The practical ruin point is the drawdown at which you change the plan, and it should be the one you measure against.

Using best-case inputs. A win rate from a short hot streak or an untested backtest makes risk of ruin look tiny. Use the numbers from your actual record, and assume they will be a little worse going forward.

Raising size to recover a drawdown. Increasing risk when the account is smallest moves you straight up the steep part of the curve. It is the fastest way to turn a recoverable drawdown into a terminal one.

Ignoring correlated positions. Three related trades at 1% each behave like one 3% trade on the day they all go wrong.

How JournalX Helps You Estimate Risk of Ruin

Risk of ruin is only as good as the inputs, and those inputs live in your journal. JournalX calculates your win rate, average win and average loss in R, and your expectancy, and you can filter them by setup, session, or symbol so each strategy is judged on its own numbers rather than a blended average. Because pre-trade planning records the risk you intended on each trade, you can also see your real risk per trade, not the figure you think you follow.

Read those next to your equity curve and maximum drawdown, and you have what you need to check whether your current size fits the drawdown you could actually tolerate. The aim is not to predict the next losing streak. It is to make sure that when it comes, you are still trading at the end of it.