Risk of Ruin Calculator

What is a risk of ruin calculator?

A risk of ruin calculator is a tool that computes risk of ruin, the probability that a run of losing trades wipes out your account before your edge has a chance to play out. The metric behind it, risk of ruin, is the chance that a losing streak drains the account to zero, or to a level you define as ruin, faster than a positive edge can compound. It is built from three inputs the tool asks for: your win rate, your risk per trade as a share of the account, and your reward-to-risk ratio, the size of the average win against the average loss. The closed-form model it uses is the advantage formula popularised by Ralph Vince, a simplification of the classic gambler's ruin problem, which turns those three numbers into a single probability.

Why is the risk of ruin calculator important for trading?

The risk of ruin calculator is important for trading because a strategy that is profitable on paper can still empty the account if the position size is too large. A positive edge only pays off over a long run of trades, and a normal losing streak can arrive first, so the cost of ignoring risk of ruin is measured in blown accounts, not in missed optimisation. The calculator puts a number on that danger before any money is committed, which is exactly when the sizing decision can still be changed.

Traders reach for the risk of ruin calculator at the moment they size a strategy, before fixing the risk per trade and before placing the trade, not after a drawdown has already happened. You run it whenever an input changes: a new win rate from a longer track record, a different risk per trade, or a shift in your reward-to-risk ratio. Sizing to survive the worst streak is the core discipline of online trading, and quantifying the chance of ruin first is what turns "trade smaller" from a slogan into a measured decision.

How do you use the risk of ruin calculator in forex trading?

To use the risk of ruin calculator, enter your win rate, your risk per trade and your reward-to-risk ratio, and the tool returns the probability that a losing streak blows your account.

The steps to use the risk of ruin calculator are listed below:

1. Enter your win rate. This is the share of your trades that end in profit, taken from a backtest or a real track record, and it is the probability the model builds the edge from.
2. Set your risk per trade. This is the percentage of the account you lose when a trade hits its stop, and it is the single most powerful lever over the result.
3. Enter your reward-to-risk ratio. This is your average win divided by your average loss, so an even-money strategy is 1 and a setup that targets twice its risk is 2.

Open Advanced options to set a ruin threshold, the drawdown you personally treat as ruin: the default is 100% for a fully emptied account, but you can set it to 50% if losing half the account is your practical point of no return. Built for the risk-management side of forex trading, where high leverage makes oversizing easy, the calculator recomputes the probability each time you press Calculate.

What formula does the risk of ruin calculator use?

The formula the risk of ruin calculator uses is a closed-form approximation that first measures your edge per trade, then raises the ratio of losing to winning odds to the number of capital units you hold before ruin.

In this model, W is your win rate as a decimal, R is your reward-to-risk ratio, edge is your expected gain per trade in units of the amount you risk, and units is the ruin threshold divided by your risk per trade, the number of full-size losses that would end the account. Plugging in the anchor values, ((1 − 0.10) ÷ (1 + 0.10)) ^ 10 = (0.9 ÷ 1.1) ^ 10 = 13.44%. The formula assumes a constant bet size and ignores the variance of the payoff when R is not 1, and if edge is zero or negative it returns a risk of ruin of 100%, because no money management rescues a strategy with no edge.

What is an example of a risk of ruin calculation?

An example of a risk of ruin calculation is a 55% win rate risking 10% per trade at an even-money reward-to-risk of 1, which produces a risk of ruin of 13.44%, worked out as follows:

1. Edge per trade = 0.55 × (1 + 1) − 1 = 0.10, a genuinely positive expectancy.
2. Capital units = 100% ÷ 10% = 10, the number of full-size losses that would empty the account.
3. Risk of ruin = ((1 − 0.10) ÷ (1 + 0.10)) ^ 10 = (0.9 ÷ 1.1) ^ 10 = 13.44%.

The result traders find surprising is that a genuinely profitable strategy, one with a positive edge, still carries a roughly 13% chance of emptying the account, purely because risking 10% per trade is far too aggressive. That 13.44% is the tool's own output for those inputs, and it is the clearest argument for lowering the risk per trade.

How do you read the risk of ruin calculator's result?

You read the risk of ruin calculator's result as a probability where lower is safer, and the headline figure sorts into a few practical bands. A result of 100% means your edge is zero or negative and ruin is effectively certain, above 20% is dangerous, 5% to 20% is risky, 1% to 5% is acceptable, and below 1% is robust.

As a working benchmark, professional traders keep their risk of ruin below 5%, and many aim for well under 1%. This figure is practitioner lore repeated by trading educators such as 2ndSkies and QuantifiedStrategies, not an academically fixed threshold, so treat it as a widely used rule of thumb rather than a law. The target is reachable because risk of ruin does not fall in a straight line as you cut your risk per trade, it collapses. Holding the same 55% win rate and even-money payoff, the probability drops sharply as risk per trade shrinks:

Halving the risk per trade from 10% to 5% cuts the risk of ruin from about 13% to under 2%, roughly a sevenfold improvement rather than a halving, which is why keeping risk per trade at 1% to 2% is the fastest way to push the probability toward zero. A low reading is not a guarantee, because the model assumes your edge and bet size stay constant, but as a relative gauge it shows clearly which sizing decisions are survivable before you commit to them.

What are the limits of the risk of ruin calculator?

The risk of ruin calculator gives an estimate that is only as reliable as the numbers you feed it, and it leaves out several real-world frictions that a live equity curve does not. The win rate and reward-to-risk you enter are assumptions about the future, so if your historical win rate does not persist the true probability shifts with it, which is the ordinary garbage-in, garbage-out limit of any model.

The model also assumes a constant bet size and a fixed edge, and it ignores the variance of the payoff when the reward-to-risk is not 1, so it describes a simplified process rather than the exact path your account takes. It does not include spread, commissions or slippage, and those costs quietly erode your effective edge on every trade; a marginal strategy pushed toward the zero-edge line by trading costs sees its risk of ruin jump to 100%, which is why execution costs matter to the number even though the tool does not model them. Finally, this is a closed-form approximation, not a Monte Carlo simulation of the equity curve, and it is an educational tool, not financial advice; complementary metrics such as drawdown and Kelly, covered by the related calculators below, fill in the parts it leaves out.

What are common mistakes when using the risk of ruin calculator in risk management?

The most common mistakes when using the risk of ruin calculator are sizing too large, treating a positive edge as automatically safe, and ignoring how steeply position size drives the result. Each one is a lapse in risk management that leaves the real probability of ruin higher than the trader assumes.

• Over-sizing the risk per trade. Risking 5% or 10% per trade feels bold, but because the effect is exponential it can lift the risk of ruin from negligible to dangerous even when the edge is real.
• Treating a positive edge as safe. A winning strategy is not automatically a surviving one, and the 55% win rate example still carries a 13% risk of ruin, so a positive edge is a starting condition, not a guarantee.
• Sizing off balance instead of equity. When open losing trades have pulled your equity below your account balance, sizing new trades off the balance quietly raises your true risk per trade above what you entered.
• Assuming the past win rate persists. A win rate measured on a favourable market run may not hold, so stress-test the result with a lower figure before you trust it.

Keeping the risk per trade in the 1% to 2% range is the single habit that neutralises most of these mistakes at once.

What is the difference between risk of ruin calculation and drawdown calculation?

A risk of ruin calculation and a drawdown calculation both measure loss, but they answer different questions: a drawdown calculation measures how far you have already fallen from a peak, while a risk of ruin calculation estimates the probability of falling so far you never recover. They are the two loss metrics most often confused, because both describe losing money, yet one is a realised measurement and the other is a forward-looking probability.

A drawdown tells you the size of the hole you are already in and how much gain it will take to climb out, whereas risk of ruin tells you the odds of digging a hole you cannot climb out of at all. Read together they cover both halves of loss: how bad it has been, and how likely it is to become fatal.

Which calculators are related to the risk of ruin calculator?

The calculators related to the risk of ruin calculator sit in the same risk and position-sizing workflow, from setting the size that drives the probability to tracking the losses it warns about.

The calculators related to the risk of ruin calculator are listed below:

• Position size calculator: sets the risk per trade that is the single biggest lever over your risk of ruin.
• Kelly criterion calculator: finds the mathematically optimal bet size, and staying at a fraction of it keeps the risk of ruin low.
• Win rate calculator: works out the win rate that feeds directly into the risk of ruin formula.
• Drawdown calculator: measures the peak-to-trough loss whose survivability risk of ruin estimates.
• Sharpe ratio calculator: judges the risk-adjusted return of the system behind your edge.
• Percentage gain calculator: shows the outsized gain needed to recover from a deep loss, the maths that makes ruin so hard to reverse.

FAQ

This tool is for education, not financial advice. Trading on margin carries a high risk of losing money rapidly. Size every trade to a loss you can survive.