Risk of ruin is the probability that your trading losses become big enough that recovery is no longer realistic. In practice it comes down to three inputs: how often you win, how much you win compared with what you lose, and what fraction of your account you put on each trade. Of the three, the third is the one you control completely, and it usually decides whether you are still trading in a year.
Below we walk through the formula, a worked example with real numbers, how it applies to forex under UK rules, and the hard rules that bring the odds down.
TL;DR
- Risk of ruin is the chance your account reaches a loss boundary you defined in advance, such as a 50% drawdown, before you reach your goals.
- The three drivers are win rate, reward-to-risk and risk per trade. Sizing often dominates the other two.
- With no edge, ruin is certain over time, whatever size you trade. With a small edge, risking 1% to 2% per trade keeps ruin very unlikely in the simple model.
- The formula is a model, not a promise. Fat tails, rising volatility and changing win rates make real risk higher than the neat output.
- Fix your ruin line, cap your risk per trade, and cut size automatically during a drawdown.
Table of Contents
- What risk of ruin means for a trading account
- The three inputs that decide your odds
- The risk of ruin formula
- A worked example, step by step
- Why the formula flatters you
- Losing streaks are normal, not a signal
- Risk of ruin in forex: leverage and UK rules
- How much should you risk per trade?
- How to lower your risk of ruin
- Our perspective: ruin is a behaviour problem first
- Build the habit with structure
- FAQ
- Sources
What risk of ruin means for a trading account
The standard definition is simple: risk of ruin is the probability that losses from trading, investing or gambling become significant enough to make recovery impossible. Notice that it says nothing about going to exactly zero. Most traders are “ruined” long before that.
So the first job is to define your own ruin line. Some examples:
- Your account falls 50%, and you now need a 100% gain just to get back to even.
- Your account drops below the minimum you need to trade your system properly.
- You lose the amount you are mentally prepared to lose, and you start revenge trading.
That last one matters. When the account is deep in the red, the brain stops trading the chart and starts trading the pain. Decision quality drops, size creeps up, and the real ruin line turns out to be the psychological one. Pick a number you can actually live with, because the maths below depends on it.
The three inputs that decide your odds
Nauzer Balsara’s published analysis identifies the same trio: probability of success, payoff ratio and the fraction of capital exposed. Ruin risk rises as the capital exposed rises, and it falls as the success probability or the payoff ratio goes up.
Win rate. The share of trades that make money. Higher is better, but alone it tells you almost nothing. A system can win 70% of the time and still lose money if the losers are bigger than the winners and costs eat the rest.
Reward-to-risk. The average win divided by the average loss. For a reward-to-risk ratio R, the break-even win rate before costs is 1/(1+R): 50% at 1:1, 40% at 1:1.5, 33.3% at 1:2 and 25% at 1:3. Spreads and slippage push the real figure higher. If you want the full picture of how these two trade off, we cover it in win rate vs risk/reward.
Risk per trade. The slice of the account you lose if the stop is hit. This is the lever that turns a survivable losing streak into a fatal one.
There is a fourth thing hiding behind these: expectancy. It combines the first two: average win times win rate, minus average loss times loss rate. A 50% win rate with a 2:1 payoff gives 0.5 units of expectancy per unit risked. If expectancy is zero or negative, no position-sizing trick saves you. Our guide to converting expectancy into R shows how to test it per setup.
The risk of ruin formula
The general approach models your equity as a random walk, using a starting value, a mean and a standard deviation. That version gets complicated quickly. Traders usually rely on a simplified version that assumes every trade wins or loses the same amount (a 1:1 payoff):
Risk of ruin = ((1 − Edge) ÷ (1 + Edge)) ^ Units
- Edge = win rate minus loss rate. A 55% win rate gives an edge of 0.55 − 0.45 = 0.10.
- Units = how many losing trades in a row would take you to your ruin line. If you risk 2% per trade and ruin is a 100% loss, that is 50 units. If your ruin line is a 50% drawdown, it is 25 units.
Read it carefully and the logic is obvious. The base is a number below 1 whenever you have an edge. Units is the exponent, so the more units of risk you have in the bank, the faster the probability collapses toward zero. Cut your risk per trade and you raise the exponent. That is why the exponent does the damage, in both directions.
If your edge is zero, the base is exactly 1, and 1 to any power is 1. That is certain ruin. No edge, no survival, only a delay.
A worked example, step by step
Take a trader with a 55% win rate and a 1:1 payoff. This is an illustration of the simplified model, not a forecast for any real strategy.
- Edge = 0.55 − 0.45 = 0.10.
- Base = (1 − 0.10) ÷ (1 + 0.10) = 0.9 ÷ 1.1 = 0.818.
- Choose a risk per trade, work out the units, and raise the base to that power. Ruin here means losing the entire account.
| Risk per trade | Units | Risk of ruin (approx.) |
|---|---|---|
| 1% | 100 | Effectively zero |
| 2% | 50 | 0.004% |
| 5% | 20 | 1.8% |
| 10% | 10 | 13.4% |
| 25% | 4 | 44.8% |
Same strategy, same win rate, same payoff. The only thing that changed is size, and the odds went from “effectively zero” to “nearly a coin flip”. This matches Balsara’s finding that sizing can dominate survival even when the success probability and payoff ratio stay the same.
Now make the edge thinner. Keep the 1:1 payoff but drop the win rate to 52%, so the edge is 0.04 and the base is 0.96 ÷ 1.04 = 0.923.
| Risk per trade | Units | Risk of ruin (approx.) |
|---|---|---|
| 1% | 100 | 0.03% |
| 2% | 50 | 1.8% |
| 5% | 20 | 20.2% |
A small edge needs much smaller size. At 5% per trade, this trader has roughly a one-in-five chance of losing everything, with a strategy that is profitable on paper. Many people who say “my system works but I keep blowing up” are looking at exactly this table.
Why the formula flatters you
The neat output deserves suspicion. Three reasons:
Markets have fat tails. The formulas assume a tidy distribution, but markets usually have fat-tailed distributions, and the results are sensitive to the standard deviation. Small changes in inputs can make the output badly inaccurate.
Volatility changes. In some models, doubling volatility can lift the probability of ruin from single digits to over 40%. That is the case for smaller positions when the market gets wild, not for the same size all the time.
Your history is not a limit. The same source notes that traders treat maximum drawdown as a hard ceiling when it is only a historical observation. The next drawdown can be deeper.
Add one more: your win rate is an estimate. If you have 40 trades behind it, the true figure could be well above or below. Treat the result as a way to compare sizing choices, never as a safety certificate.
Losing streaks are normal, not a signal
The formula talks about streaks, so it helps to know how common they are. For a strategy that wins 45% of the time, one CMC Markets Funded example puts any specified run of five losses at about 5%, but at least one run of five in 100 trades at about 92%. A run of six at least once in 100 trades comes in at about 73%.
Read that again. A sequence that looks like “my system broke” is statistically expected. If five losses at 2% each cost you roughly 10%, you survive and carry on. If five losses at 10% each cost you around 41%, you are in a different operating system entirely: tilted, desperate, sizing up to win it back. The streak is the same. The sizing decided the outcome.
Risk of ruin in forex: leverage and UK rules
Leverage is what makes sizing mistakes so easy in forex. A small price move on a large position can wipe out a meaningful part of the account before you react.
For UK retail clients, the FCA has set some guardrails. For CFDs, leverage is limited between 30:1 and 2:1, firms must close positions when funds fall to 50% of the margin needed, and you cannot lose more than the total funds in your trading account. Those rules cap the damage to your deposit. They do not protect the deposit itself: ruin still arrives if equity runs down to the close-out level.
So the rules are a floor, not a plan. The usual professional habit is to size from the stop, not from the leverage available. The position size formula is account balance times risk percentage, divided by stop-loss in pips times pip value.
Example: a £10,000 account, risking 1% (£100), with a 25 pip stop and a pip value of £1 per pip per lot-equivalent unit you are trading. Position size = £100 ÷ (25 × £1) = 4 units of that pip value. Whatever leverage the broker offers, if the stop hits, you lose about £100. If you want a deeper walk-through, see our pieces on risk per trade and risk management and position sizing in practice.
How much should you risk per trade?
Forex risk management commonly keeps exposure on a single trade between 1% and 2% of account equity. Our tables show why. At 1% to 2%, even a modest edge leaves ruin very unlikely, and a run of six or seven losses is a bruise rather than a disaster.
A few practical notes:
- Start at 1% if you are new or your sample of trades is small. You can earn the right to size up with data.
- The number applies to cash at risk at the stop, not to the position’s nominal size.
- Several open trades on correlated pairs count as one bigger bet. Three long positions against the dollar are not three separate 1% risks.
- Costs matter. Spreads and slippage widen your real loss beyond the planned stop, so leave some room.
We go deeper on this in the 1% rule for UK forex traders and the 2% risk rule.
How to lower your risk of ruin
Here is the sequence we would follow, in order.
- Set your ruin line in writing. A drawdown percentage you will not cross, for example 20% of the account, at which you stop and review.
- Confirm you have an edge. Log at least a few dozen trades per setup, then calculate win rate, average win, average loss and expectancy. If expectancy is not positive after costs, fix the system before you touch size.
- Cap risk per trade. 1% is a sensible default, 2% a ceiling for most.
- Scale down in drawdown. One published guideline from the International Trading Institute is to cut per-trade risk by 25% after a 5% drawdown, by 50% after 10% to 15%, and halt beyond 15%. Make it a hard rule, decided when you are calm.
- Cap total open risk. Limit the sum of risk across all open positions, and count correlated pairs together.
- Shrink size when volatility spikes. If the market’s average range doubles, your stop probably widens. Keep the cash risk fixed, so the position gets smaller.
- Check your reward-to-risk before entry. Skip trades where the maths does not work. Our pre-entry checklist walks through it.
- Review weekly. Recalculate your stats and your table. If the win rate has slipped, your ruin number has moved too.
If you are already in a hole, reducing drawdown step by step is the next read, and risk management rules new traders must know covers the fundamentals.
Our perspective: ruin is a behaviour problem first
We have spent more than 18 years trading live markets, and the pattern repeats. Almost nobody is wiped out by a single bad idea. They are wiped out by a sequence: a normal losing streak, then a bigger size to “get it back”, then another loss, then a trade with no stop. The formula describes the end of that story. The beginning is a decision made under pressure.
That is why we treat risk per trade as a hard rule rather than a preference. If you only decide your size in the moment, the pain decides it for you. If the number is fixed in advance, a losing streak is just a statistic and you keep your decision quality.
We also think traders spend too long on entries and too little on sizing. A mediocre entry with disciplined size survives. A great entry with reckless size eventually gets you. The maths above is not a reason to fear the market. It is a reason to relax, because the part that decides survival is the part you control.
— Gabriel
Build the habit with structure
Knowing the numbers is easy. Applying them on the fifth loss of the week is harder. That is where structure and feedback help: a journal that tracks your real win rate and expectancy, a risk plan you review with someone, and a community that holds you to your rules.
At Trader Gibkey, we teach price action trading with risk management and trading psychology built in, plus journaling tools, live sessions and a supportive community. Our Price Action (Core) plan is £149 per month, and if you prefer one-to-one feedback on your sizing and risk plan, a Single Session Mentorship is €149 per session. You can see everything on our main page.
If you would rather start free, take your last 30 trades, calculate your win rate and average win and loss, and run them through the table above. It takes under an hour and tells you more than another strategy video will.
FAQ
What is a good risk of ruin percentage?
A common target is below 1%. Many practitioners treat anything above a few percent as too high, because the model usually understates real risk. Lower risk per trade is the quickest way to get there.
Does risk of ruin apply to forex?
Yes. Leverage makes oversized positions easy, so ruin comes faster. In the UK, FCA rules cap retail CFD leverage and protect you from losing more than your account, but you can still lose the whole deposit.
What risk per trade keeps ruin unlikely?
Most traders stay at 1% to 2% of equity per trade. With a modest, tested edge, that leaves ruin very unlikely in the simple model. With no edge, no size is safe.
Sources
- Risk of Ruin: What it Means, How it Works, Controlling it (Investopedia)
- Risk of ruin (Wikipedia)
- Minimizing Your Risk Of Ruin (George Mason University, 2009)
- Appreciating the Risk of Ruin, Stocks & Commodities V. 10:12
- FCA PS19/18: Restricting contract for difference products sold to retail clients
- Judge a strategy by R multiples and expectancy (CMC Markets Funded)
- Stability Statistics (FXStreet Learning Center)
- Forex risk management strategies for UK traders (CMC Markets)
- Position Sizing in Trading: How to Calculate Risk Per Trade (MonkeyTrade)