Risk of Ruin Calculator
Free Risk ruin Calculator for risk management. Enter your numbers to see returns, costs, and optimized scenarios instantly.
Calculator
Adjust values & calculateAverage winning trade / average losing trade
Account loss percentage that defines ruin
Risk of Ruin by Position Size
Formula
Risk of ruin is calculated by raising the ratio (1-edge)/(1+edge) to the power of N, where N represents the number of risk units needed to reach the ruin threshold. The edge is determined by multiplying win rate by (1 + win/loss ratio) and subtracting 1. Kelly Criterion = WR - LR / (W/L ratio).
Last reviewed: December 2025
Worked Examples
Example 1: Conservative Day Trader
Example 2: Aggressive Swing Trader
Background & Theory
The Risk of Ruin Calculator applies the following established principles and formulas. Foreign exchange markets facilitate the conversion of one currency into another and serve as the largest and most liquid financial markets in the world, with daily turnover exceeding seven trillion US dollars. Exchange rates are quoted as currency pairs, expressing the price of one unit of a base currency in terms of a quote currency. For example, a EUR/USD rate of 1.0850 means one euro buys 1.0850 US dollars. The smallest standardized price movement in most pairs is the pip, typically the fourth decimal place, with a value of 0.0001 per unit for USD-denominated pairs. The bid price is the rate at which a dealer will buy the base currency, while the ask price is the rate at which it will sell. The spread between bid and ask represents the dealer's compensation and varies with liquidity and volatility. Leverage amplifies both gains and losses by allowing traders to control positions larger than their deposited margin. A 100:1 leverage ratio means a one-percent adverse move eliminates the entire margin, making position sizing and risk management critical. Two parity conditions from international economics anchor exchange rate theory. Purchasing Power Parity (PPP) holds that exchange rates should adjust over time so that identical goods trade at equivalent prices across countries: S = P_d / P_f, where S is the spot rate and P_d and P_f are domestic and foreign price levels. PPP performs well over long horizons but poorly in the short run due to trade barriers, non-tradable goods, and capital flows. Covered Interest Rate Parity (CIRP) is a near-arbitrage condition stating that forward exchange rate premiums or discounts exactly offset interest rate differentials between two currencies: F/S = (1 + r_d) / (1 + r_f). Deviations from CIRP create riskless arbitrage opportunities that traders rapidly eliminate. Uncovered Interest Rate Parity posits that high-yielding currencies should depreciate to offset their interest advantage, though empirical evidence is mixed and the carry trade — borrowing in low-rate currencies to invest in high-rate ones — has generated persistent returns.
History
The history behind the Risk of Ruin Calculator traces back through the following developments. For much of the nineteenth century and early twentieth century, the international monetary system operated under the classical gold standard, under which each participating currency was fixed to a defined weight of gold, making bilateral exchange rates effectively constant. The system provided price stability and facilitated global trade but constrained governments' ability to respond to economic downturns. World War One shattered the gold standard as nations suspended convertibility to finance wartime expenditures. The interwar period saw attempts to restore gold convertibility, most notably the British return to the gold standard in 1925 at the pre-war parity, a decision criticized by John Maynard Keynes as deflationary. The Great Depression forced widespread currency devaluations and the effective collapse of the international gold standard by the early 1930s. The Bretton Woods Conference of July 1944 established a new order in which member currencies were pegged to the US dollar, while the dollar alone was convertible into gold at 35 dollars per troy ounce. The International Monetary Fund and World Bank were created at the same conference to oversee the system. Bretton Woods delivered exchange rate stability during the postwar growth era but came under strain as US deficits and European dollar accumulation outpaced American gold reserves. On August 15, 1971, President Nixon announced the suspension of dollar-gold convertibility — the so-called Nixon Shock — effectively ending the Bretton Woods system. By 1973, major currencies had transitioned to floating exchange rates determined by market supply and demand, a regime that has persisted. On September 16, 1992, hedge fund manager George Soros shorted the British pound against the European Exchange Rate Mechanism constraints, forcing the UK's withdrawal in what became known as Black Wednesday. Electronic trading platforms emerged in the 1990s and 2000s, replacing voice-brokered interbank markets and dramatically reducing transaction costs for institutional and retail participants alike.
Frequently Asked Questions
Formula
RoR = ((1 - edge) / (1 + edge))^N where edge = WR x (1 + W/L ratio) - 1
Risk of ruin is calculated by raising the ratio (1-edge)/(1+edge) to the power of N, where N represents the number of risk units needed to reach the ruin threshold. The edge is determined by multiplying win rate by (1 + win/loss ratio) and subtracting 1. Kelly Criterion = WR - LR / (W/L ratio).
Frequently Asked Questions
What is the risk of ruin in trading and why does it matter?
Risk of ruin is the probability that a trader will lose enough capital to reach a point where they can no longer trade effectively, typically defined as losing a specified percentage of their account balance. This concept is fundamental to trading survival because even profitable strategies can lead to account blowup if position sizing is too aggressive. A trader with a genuine 55 percent win rate and positive expected value can still face ruin if they risk too much per trade, as a string of losses can deplete the account before the statistical edge manifests. The mathematics of risk of ruin demonstrates that capital preservation is not merely conservative advice but a mathematical necessity. Professional traders and fund managers calculate their risk of ruin to determine the maximum acceptable position size that keeps the probability of catastrophic loss below an acceptable threshold, typically under 1 to 5 percent.
How does position sizing affect the probability of ruin?
Position sizing has an exponential impact on risk of ruin, making it arguably the most important variable in a trading system. Doubling the risk per trade does not merely double the risk of ruin — it can increase it by an order of magnitude or more. For example, a trader with a 55 percent win rate and 1.5 reward-to-risk ratio might have a 0.1 percent risk of ruin when risking 1 percent per trade, but that same trader risking 5 percent per trade could face a 20 percent or higher probability of ruin. This dramatic escalation occurs because larger position sizes require fewer consecutive losses to reach the ruin threshold, and the probability of experiencing a specific losing streak increases substantially over hundreds or thousands of trades. Professional risk managers typically recommend never risking more than 1 to 2 percent of account equity on any single trade to maintain an acceptably low risk of ruin over a trading career.
What is the Kelly Criterion and how does it relate to risk of ruin?
The Kelly Criterion is a mathematical formula that calculates the optimal fraction of capital to risk on each trade to maximize the long-term geometric growth rate of the portfolio. The formula is Kelly Fraction equals Win Rate minus (Loss Rate divided by Win-to-Loss Ratio). While the full Kelly percentage theoretically maximizes growth, it also produces significant drawdowns and a relatively high risk of ruin in practice. Most professional traders use fractional Kelly, typically one-quarter to one-half of the full Kelly amount, to dramatically reduce volatility and risk of ruin while sacrificing only modest long-term growth. For instance, if full Kelly suggests risking 8 percent per trade, using half-Kelly at 4 percent cuts the growth rate by only about 25 percent but reduces the risk of a 50 percent drawdown by more than 75 percent. This demonstrates the asymmetric benefit of conservative position sizing.
How do win rate and reward-to-risk ratio interact in risk calculations?
Win rate and reward-to-risk ratio are the two components that define a trading edge, and they interact multiplicatively to determine expected value and risk of ruin. A trader can be profitable with a low win rate if the reward-to-risk ratio compensates sufficiently. For example, a trend-following system with only 35 percent win rate but a 3:1 average winner-to-loser ratio has a positive expected value of 0.35 times 3 minus 0.65 equals 0.40 per unit risked. Conversely, a scalping system with 70 percent win rate but only 0.8:1 reward ratio has an edge of 0.70 times 0.8 minus 0.30 equals 0.26 per unit risked. The first system has a higher mathematical edge despite winning far less frequently. When calculating risk of ruin, both variables feed into the edge calculation, and even small changes in either can dramatically alter the ruin probability, especially at higher risk-per-trade levels.
What is a safe risk of ruin percentage for different types of traders?
Acceptable risk of ruin thresholds vary by trader type, capital base, and ability to replenish funds. Professional fund managers and institutional traders typically target a risk of ruin below 0.1 percent, meaning there is less than a 1-in-1000 chance of reaching their maximum drawdown threshold. Full-time independent traders who depend on trading income generally aim for under 1 percent risk of ruin, providing strong statistical confidence in long-term survival. Part-time traders with separate income sources may accept 2 to 5 percent risk of ruin since they can potentially replenish trading capital from other earnings. Beginners and traders still developing their edge should be the most conservative, targeting well under 1 percent, because their actual win rate and reward statistics often deteriorate under live market conditions compared to backtesting results. A common mistake is estimating risk of ruin using optimistic performance parameters rather than worst-case realistic figures.
What are the different lot sizes in forex and how do they affect risk?
A standard lot is 100,000 units, a mini lot is 10,000, a micro lot is 1,000, and a nano lot is 100 units of the base currency. Smaller lots reduce your dollar-per-pip exposure, making them suitable for beginners or smaller accounts.
References
Reviewed by Daniel Agrici, Founder & Lead Developer · Editorial policy