Risk of Ruin Calculator

Risk of Ruin Calculator: Know Your Odds Before You Blow Up Your Account

This risk of ruin calculator takes your win rate and reward-to-risk ratio and turns them into a single, honest number: the probability that your current trading approach eventually wipes out your account. Enter your stats, set how much you risk per trade, and the calculator instantly shows your risk of ruin percentage, your statistical edge, your expectancy, and a Kelly criterion sizing suggestion — all in one place.

Traders search for tools like a risk of ruin calculator, probability of ruin calculator, account blow up calculator, and trading risk of ruin formula because most people size their trades by feel rather than by math. This calculator replaces the guesswork with a clear number, and shows exactly how much that number changes as you adjust position size, so you can find a risk level that lets your edge actually play out over time.

What Does Risk of Ruin Actually Mean?

Risk of ruin is a concept borrowed from gambling theory and applied to trading. It answers a simple question: if you keep trading this exact system, with this exact win rate, this exact reward-to-risk ratio, and this exact position size, what are the odds that a losing streak eventually drags your account down to a defined ruin level, such as losing it completely?

It is not a prediction of what will happen on your very next trade. It is a long-run statistical estimate based on the two things that matter most for survival: whether your system actually has a positive edge, and how much of your capital you expose to that edge on each trade. A system can have a great win rate and still carry high risk of ruin if the position size is too aggressive, and a modest edge can survive comfortably if the risk per trade is kept small.

How to Use This Risk of Ruin Calculator

Start with your win rate — the percentage of trades that close as winners, based on your trading journal or backtest results. Then enter your reward-to-risk ratio, meaning how many units you make on an average win compared with how many units you lose on an average loss. A 2:1 reward-to-risk ratio means your typical winner is twice the size of your typical loser.

Next, enter the percentage of your account you risk on a single trade — this is your position size, not your stop-loss distance in price. The calculator then works out your risk of ruin instantly. Use the advanced Ruin Threshold setting if you want to measure the odds of hitting a smaller drawdown, such as a 50% account loss or a prop-firm's maximum drawdown limit, instead of a full 100% wipeout.

• Win Rate: the percentage of trades that end as winners.
• Reward-to-Risk (R2R): average win size divided by average loss size, in R multiples.
• Risk per Trade: the percentage of account capital risked on one trade.
• Ruin Threshold (advanced): what percentage loss counts as 'ruin' — defaults to 100%.

The Risk of Ruin Formula Explained

This calculator uses the widely referenced edge-based risk of ruin formula for trading systems with unequal win and loss sizes. First, it calculates your statistical edge by comparing your weighted win rate against your weighted loss rate: Edge equals (Win Rate multiplied by R2R, minus Loss Rate), divided by (Win Rate multiplied by R2R, plus Loss Rate).

Next, it works out how many risk units fit inside your ruin threshold: Units equals the Ruin Threshold percentage divided by your Risk per Trade percentage. Finally, Risk of Ruin equals ((1 minus Edge) divided by (1 plus Edge)) raised to the power of Units. A positive edge combined with more units (smaller risk per trade) pushes this number toward zero. A weak or negative edge pushes it toward 100%, no matter how small the risk per trade is, since a losing system eventually loses everything given enough trades.

Why Position Size Matters More Than Most Traders Think

Two traders can run the exact same strategy, with the exact same win rate and reward-to-risk ratio, and end up with wildly different outcomes purely because of position size. A trader risking 0.5% per trade and a trader risking 5% per trade on the identical system are playing very different games — the second trader's risk of ruin can be dramatically higher, sometimes by a factor of ten or more, even though their edge is identical.

This happens because the risk of ruin formula raises the edge ratio to a power based on how many 'units' of risk fit inside the account. Smaller risk per trade means more units, which means more room to survive a losing streak before the ruin threshold is hit. This is why professional risk management usually focuses as much on position sizing as it does on finding a good entry signal.

Kelly Criterion and Position Sizing

The Kelly criterion is a formula that calculates the mathematically optimal percentage of capital to risk per trade in order to maximize long-term account growth, given a specific win rate and reward-to-risk ratio. This calculator shows both the full Kelly percentage and a Half-Kelly percentage, since risking the full Kelly amount tends to produce large equity swings that most traders find psychologically difficult to sit through.

Half-Kelly, or even a quarter of the Kelly value, is a common, more conservative choice among traders and portfolio managers, because it sacrifices some theoretical growth rate in exchange for a noticeably smoother equity curve and a lower risk of ruin. If your current risk per trade sits well above the Kelly percentage shown here, that is usually a sign your position size is too large for your edge.

Risk of Ruin Calculator Keywords People Actually Search For

People land on tools like this searching for terms such as risk of ruin calculator, probability of ruin calculator, trading risk of ruin formula, kelly criterion calculator, win rate risk to reward calculator, account blow up calculator, position sizing risk of ruin, and risk of ruin forex. Almost every one of these searches comes down to the same underlying question: given my stats, how much can I safely risk per trade without eventually losing everything?

This calculator answers that question directly. It combines the core risk of ruin percentage with your statistical edge, your expectancy per trade in both R multiples and percentage terms, a Kelly and Half-Kelly sizing suggestion, and a full sensitivity table showing how ruin probability changes across a range of risk-per-trade levels, all on a single page with a copy summary and CSV export.

How Traders Use Risk of Ruin in Practice

Many traders run this kind of calculation before committing real capital to a new strategy, using backtested or forward-tested win rate and reward-to-risk numbers to check whether the intended position size is survivable. If the risk of ruin comes back uncomfortably high, the fix is almost always to reduce risk per trade rather than abandon the strategy outright, assuming the underlying edge is genuinely positive.

Others use it as an ongoing check whenever their live trading statistics change. A win rate that drifts lower during a rough month, or a reward-to-risk ratio that shrinks because trades are being closed too early, both raise risk of ruin even if the position size never changes. Revisiting the numbers periodically, instead of only once at the start, helps catch a rising ruin probability before it turns into an actual drawdown.

Limitations of the Risk of Ruin Formula

This formula assumes a fixed win rate and fixed reward-to-risk ratio that stay constant over time, and it assumes trade outcomes are independent of one another, meaning one trade's result does not influence the next. Real trading rarely matches these assumptions perfectly — win rates drift, reward-to-risk ratios vary trade to trade, and psychological factors like revenge trading after a loss can break the independence assumption entirely.

Treat the output as a useful estimate and an early-warning signal, not an exact guarantee. A very high risk of ruin number is a clear signal to cut position size or rethink the strategy, while a low number is reassuring but does not eliminate the need for basic risk controls like a maximum daily loss limit or a rule to stop trading after a defined losing streak.

Reducing Your Risk of Ruin: Practical Tips

The fastest way to lower risk of ruin is almost always to reduce risk per trade, since the formula is extremely sensitive to this input. Even a small cut, from 2% down to 1% per trade, can meaningfully drop the ruin probability for a system with a modest edge. The sensitivity table in this calculator makes that trade-off visible instantly, without needing to run the math by hand for every risk level.

Beyond position size, focus on protecting the two inputs that build your edge: win rate and reward-to-risk. Cutting losers quickly and letting winners run further both help keep the reward-to-risk ratio healthy, while a disciplined, rules-based entry process tends to protect win rate better than discretionary, emotion-driven entries. A small, consistent edge, sized conservatively, tends to survive far longer than a flashy edge sized too aggressively.

Risk of Ruin for Different Trading Styles

Day traders and scalpers who take many trades per day are especially exposed to risk of ruin math, since a high trade frequency means a losing streak can unfold within days rather than months. Keeping risk per trade low is particularly important for high-frequency styles, since the formula compounds quickly when many risk units are consumed in a short period.

Swing and position traders, who hold fewer trades over longer periods, often have more room to size slightly larger per trade without the same speed of drawdown, simply because fewer trades occur in a given stretch of time. Even so, the underlying math does not change: a system with a weak or negative edge will eventually reach ruin at any trade frequency, it just may take longer to get there.

Risk of Ruin vs Drawdown: What Is the Difference?

Drawdown is the actual, historical dip in your account balance from a previous peak — it is something you can measure directly from your trading history or backtest equity curve. Risk of ruin, on the other hand, is a forward-looking probability estimate based on your statistical inputs, not a measurement of what has already happened.

The two are closely related: a system with a high risk of ruin will tend to produce large, painful drawdowns more often over time, while a system with a low risk of ruin tends to keep drawdowns shallower and shorter. Checking both together gives a fuller picture — your trading journal shows what has actually happened, and this calculator estimates how likely a much worse outcome still is if nothing about your sizing or edge changes.

A Simple Example: Same Edge, Different Position Size

Imagine two traders both running a system with a 45% win rate and a 2:1 reward-to-risk ratio — a real, positive edge on paper. Trader A risks 0.5% of the account per trade. Trader B risks 4% per trade on the exact same signals. Because the risk of ruin formula raises the edge ratio to a power based on how many risk units fit inside the account, Trader A ends up with a dramatically lower risk of ruin than Trader B, even though both are trading the identical strategy with the identical edge.

This example is the core reason risk of ruin calculators exist: the strategy alone does not determine survival, the combination of strategy and position size does. Plugging your own numbers into the calculator above, then dragging the risk-per-trade input up and down, is the fastest way to see this relationship play out for your own trading stats instead of a hypothetical example.

Final Thoughts

A risk of ruin calculator turns two numbers most traders already track — win rate and reward-to-risk ratio — into a clear, honest read on how survivable a trading system actually is at a given position size. Instead of guessing whether 1% or 2% or 5% risk per trade is 'too much,' this tool shows the exact ruin probability for each, alongside a Kelly-based sizing suggestion and expectancy figures. Run your numbers here before increasing size, after a stretch of live results, or any time you want an honest gut-check on how much of your account is genuinely at risk.