Risk of Ruin Calculator

A risk of ruin calculator estimates the probability that your trading account falls far enough to hit a loss level you personally define as ruin, using your win rate, your reward to risk ratio, and the percentage you risk on each trade. Risk of ruin is the chance that a string of losses drains your capital past a point you cannot or will not recover from, for example a 50 percent drawdown. The calculator above turns four or five simple numbers into a single survival probability, so you can see, before you place a single trade on AAPL, SPY, or an ES futures contract, whether your position sizing gives your edge room to work or quietly sets you up to blow up. This page explains every input and output, shows the Monte Carlo method behind the number, and works through real examples. Nothing here is financial or tax advice.

What Risk of Ruin Actually Means

Ruin does not always mean a zero balance. In practice, most traders are ruined long before the account reaches zero, because they stop trading, lose confidence, or run out of margin. That is why this calculator lets you set a Ruin Drawdown percent. If you decide that a 50 percent loss ends your trading capital, then ruin is defined as dropping 50 percent below your starting equity at any point during the run. Risk of ruin is the probability that at least one path of trades touches that level.

The key idea is that ruin is about the journey, not just the destination. Two accounts can both end a year up 20 percent, but if one of them dipped 55 percent along the way while the other never fell below 12 percent, only one of them survived in any realistic sense. A margin call, a forced liquidation of an ES or NQ futures position, or simply the fear that follows a deep drawdown can take you out of the game even when the long run math is in your favor. Risk of ruin measures that path danger directly.

How the Calculator Works: Inputs and Outputs

The calculator above takes five inputs and returns four outputs. Each input describes your trading edge and how aggressively you deploy it. Define each one carefully, because small changes in these numbers produce large changes in the result.

• Win Rate percent: the share of your trades that finish as winners. If 55 of your last 100 SPY trades were profitable, your win rate is 55 percent.
• Reward to Risk Ratio: the size of your average winner compared with your average loser. A ratio of 2 means your average win is twice your average loss, often written as 2R where R is one unit of risk.
• Risk Per Trade percent: the fraction of your account you lose if a single trade hits its stop. Risking 2 percent of a 10,000 dollar account means a 200 dollar loss per losing trade.
• Number of Trades: how many trades the simulation runs, for example 200 or 500. Ruin can appear over a long run that a short run hides.
• Ruin Drawdown percent: the loss level you count as ruin, such as 50 percent below starting equity.

The outputs translate those inputs into risk you can act on. Risk of Ruin is the probability, from 0 to 100 percent, that a simulated account touches your ruin drawdown. Survival Rate is simply 100 minus the risk of ruin, the share of runs that finish without being wiped out. Expectancy per Trade is the average profit or loss you expect on a typical trade, expressed in R units or as a percentage of the account. Assessment is a plain label such as safe, caution, or dangerous, based on how high the risk of ruin climbs.

How to Use the Risk of Ruin Calculator

1. Pull your real numbers from your trade journal. Use your actual win rate and reward to risk ratio over at least 30 to 50 trades, not a hopeful guess.
2. Enter your true risk per trade as a percent of your current account, based on the distance from entry to stop, not the full contract or premium size.
3. Set Number of Trades to a realistic horizon, such as your expected trades over the next quarter or year.
4. Choose a Ruin Drawdown percent that reflects where you would actually quit, often 30 to 50 percent.
5. Read the Risk of Ruin and Survival Rate outputs, then check the Expectancy per Trade to confirm your edge is positive.
6. If the risk of ruin is uncomfortable, lower the Risk Per Trade percent first and rerun. It is the fastest lever you control.
7. Save the scenario, then log every future trade so you can compare the model against what really happens.

The Math and the Monte Carlo Method

Expectancy is the foundation. For a system with win rate W as a decimal and reward to risk ratio R, the expectancy in R units is W times R minus the loss rate times 1, where the loss rate is 1 minus W. As a formula: Expectancy = (W multiplied by R) minus ((1 minus W) multiplied by 1). Multiply that by your risk per trade to express it in account percent. A system with a 50 percent win rate and a 2 to 1 reward to risk ratio has an expectancy of (0.50 times 2) minus (0.50 times 1), which equals 0.50R per trade. Positive expectancy is necessary but not sufficient, because it describes the average, not the worst path.

There is a classic closed form for even money bets, where risk of ruin equals ((1 minus edge) divided by (1 plus edge)) raised to the number of risk units in your account. It is useful for intuition but assumes fixed bet sizes and only two outcomes. Real trading has varied win sizes, losing clusters, and compounding, so this calculator uses a Monte Carlo simulation instead.

A Monte Carlo simulation plays out your system thousands of times using random outcomes that match your inputs. For each simulated trade it draws a win or a loss according to your win rate, applies the win or loss size set by your reward to risk ratio and risk per trade, and updates the running balance. It repeats this for your chosen Number of Trades to complete one path, then runs that path thousands more times. The risk of ruin is the fraction of those paths that dipped to your ruin drawdown at any point. Because it samples many possible futures, it captures the ugly losing streaks that a single average calculation would miss.

Worked Examples With Real Numbers

Example 1: A Disciplined SPY Swing Trader

A trader with a 10,000 dollar account swings SPY and SPY options positions. Their win rate is 45 percent, their reward to risk ratio is 2.5, and they risk 1 percent per trade, or 100 dollars, over 300 trades, with ruin set at a 50 percent drawdown. Expectancy is (0.45 times 2.5) minus (0.55 times 1), which equals 1.125 minus 0.55, or 0.575R per trade. That is a strong positive edge. Because risk per trade is only 1 percent, a Monte Carlo run returns a risk of ruin near 0 percent and a survival rate near 100 percent. The assessment reads safe. This trader can survive long losing streaks because each loss barely dents the account.

Example 2: The Same Edge, Sized Too Big

Now take the exact same edge, a 45 percent win rate and a 2.5 reward to risk ratio, but raise risk per trade to 12 percent while trading ES futures. Expectancy is still a healthy 0.575R per trade, so the system is profitable on average. Yet at 12 percent risk, a run of six or seven losses in a row, which is common at a 45 percent win rate, can cut the account by more than half. A Monte Carlo simulation over 300 trades now returns a risk of ruin around 60 to 70 percent. The survival rate falls under 40 percent and the assessment reads dangerous. Same edge, same win rate, but oversizing turns a winning system into a coin flip on survival.

Example 3: High Win Rate That Still Blows Up

A trader sells short dated CL crude oil options and NQ premium and wins 80 percent of the time, which feels safe. But the reward to risk ratio is only 0.3, because the rare loss is large relative to the small, frequent wins. Expectancy is (0.80 times 0.3) minus (0.20 times 1), which equals 0.24 minus 0.20, or just 0.04R per trade, barely positive. If this trader risks 8 percent per trade, a couple of clustered losses among the 20 percent of losers can devastate the account. Over 200 trades the Monte Carlo risk of ruin can climb above 40 percent. A high win rate hides fragility when the losers are large and the position size is aggressive.

Risk Per Trade Reference Table

The table below holds the edge fixed at a 50 percent win rate and a 2 to 1 reward to risk ratio, an expectancy of 0.50R per trade, and shows how the estimated risk of ruin changes as risk per trade rises. Ruin is defined as a 50 percent drawdown over 200 trades. These are illustrative Monte Carlo estimates, not guarantees, but the shape is the lesson: risk of ruin explodes as risk per trade climbs.

Tips for Getting an Honest Number

• Use real journal data, not hopeful estimates. A win rate you wish you had will hide real risk of ruin.
• Recalculate after every 20 to 30 trades, because your true win rate and reward to risk ratio drift over time.
• Keep risk per trade small and fixed, commonly 1 to 2 percent, so no single trade can define your account.
• Model a long horizon. Ruin that never appears over 50 trades can be common over 500.
• Account for correlation. Five open SPY, ES, and NQ positions moving together act like one large bet, not five small ones.
• Never rely on the model alone for options. Time decay, gaps, and assignment on naked options can cause losses larger than the model assumes.
• Treat the assessment label as a starting point for a conversation with yourself, not a green light.

Common Mistakes to Avoid

The most frequent error is confusing risk per trade with position size. Risking 2 percent does not mean buying 2 percent of your account in a stock. It means the distance from your entry to your stop, times your quantity, equals 2 percent of your account. A tight stop lets you hold a larger position for the same 2 percent risk, and a wide stop demands a smaller one.

A second mistake is trusting a positive expectancy as proof of safety. Expectancy is the long run average, but ruin happens on the path, so a profitable system sized too large still fails. A third mistake is entering an inflated win rate, which flatters the result and hides the very danger you are trying to measure. Finally, many traders ignore correlation and open several positions that all rise and fall together, turning what looks like small diversified risk into one concentrated bet that the calculator, fed separate small numbers, will underestimate.

How It Supports Disciplined Journaling

A risk of ruin calculator is only as honest as the numbers you feed it, and those numbers come from a trade journal. When you log every trade, your win rate and reward to risk ratio stop being guesses and become measured facts. Rerunning the calculator with fresh data after each block of trades turns risk of ruin into a living dashboard rather than a one time exercise. If your measured win rate slips or your average loss grows, the survival rate falls, and you see it before your account does.

This is where risk of ruin connects directly to position sizing discipline. The single most powerful lever in every example above was risk per trade, the one number entirely under your control on every single trade. Journaling your planned risk, your actual risk, and the outcome lets you spot the days you quietly sized up out of confidence or revenge. Over time, keeping risk small and consistent is what separates traders who survive long enough to let their edge compound from those who had a real edge and still blew up.

Run your real numbers through the calculator above, then keep them honest by logging every trade on OneTradeJournal. When your win rate, reward to risk ratio, and risk per trade come straight from a disciplined journal instead of memory, your risk of ruin becomes a number you can trust and act on. Size small, track every trade, and give your edge the survival it needs to compound.