What is risk of ruin?
Risk of ruin is the probability that a losing streak wipes out your account before your edge pays off. It is the most important risk question in trading because it is the one you cannot recover from — a ruined account has no edge left to compound. Even a profitable system carries real risk of ruin if you bet too much per trade.
Where the idea comes from
Risk of ruin descends from the classic gambler's ruin problem in probability: a gambler making repeated bets against an opponent will, with some probability, lose their entire stake before reaching their goal. Trading is the same problem with a fuzzier edge — your "bet" is each trade, your "stake" is your account, and ruin is the equity level at which you would stop.
intuition# Two levers move risk of ruin the most:
1. risk per trade → fewer losing units between you and ruin = higher risk
2. your edge → positive expectancy makes ruin exponentially less likely
# With no edge, ruin is essentially certain given enough trades.
At 1% risk per trade it takes a long, improbable streak of losses to do serious damage, so even modest edges survive variance. At 10% per trade, a normal cold streak can end the account before the edge ever shows up. Risk of ruin is the math behind "live to trade another day."
Lowering your risk of ruin
- Risk less per trade. The single most powerful lever — see the position sizing calculator.
- Strengthen your edge. Higher win rate or reward-to-risk; quantify it with the expectancy calculator.
- Cap your bet size. Never exceed the Kelly fraction; most pros use a quarter of it.
- Estimate it directly. Use the risk of ruin calculator, then validate with a Monte Carlo simulation on your real trades.
Risk of ruin vs drawdown
Drawdown measures how far you have fallen; risk of ruin estimates the chance you fall far enough to quit or blow up. They are complementary: a strategy with a tolerable expected drawdown can still have an uncomfortable risk of ruin if the position sizing is aggressive. The CFA Institute and CFTC both stress that capital preservation — surviving — precedes return.
Frequently asked questions
What is risk of ruin in trading?
Risk of ruin is the probability that a run of losses drives your account down to a level you treat as ruined — often a 50% or 100% loss — before your edge can compound. Borrowed from gambling's gambler's-ruin problem, it is the question that every position-sizing rule is ultimately trying to answer: will I survive long enough to win?
Does a profitable system have zero risk of ruin?
No. Even a system with positive expectancy has a non-zero risk of ruin if you risk too much per trade, because variance can deliver a long losing streak before the edge shows up. Risking less per trade pushes the probability toward zero; risking a lot can ruin a profitable system through sheer bad luck.
What is the biggest driver of risk of ruin?
Risk per trade. Halving the percentage you risk per trade reduces risk of ruin far more than it reduces your expected growth, because ruin depends on the number of consecutive losing risk-units between you and the ruin line. This is the mathematical reason the 1–2%-per-trade rule is so widely taught.
How do I estimate my own risk of ruin?
Use the closed-form approximation in our risk of ruin calculator for a quick directional read, then run a Monte Carlo simulation on your real trade distribution for a faithful estimate. Monte Carlo resamples your actual trades thousands of times and counts how often the account hits your ruin threshold.