Risk of ruin is the probability that you lose enough of your capital to be knocked out of the game — either you hit zero, or you fall past the point where you would have to stop. A positive edge does not make you safe. Bet too large a slice on each trade and ruin becomes not a risk but a near-certainty over enough trades, however good the system. It is the number that decides whether a winning strategy survives long enough to win.
What it is
Risk of ruin is the chance that a run of losses drains your account below the level at which you can keep trading. "Ruin" does not have to mean zero — for most traders it is the point where the account is too small to trade the same size, or where a prop-firm limit trips and the account is closed. Three things drive it: your win rate, your edge (how big the wins are against the losses), and, above all, how much you risk per trade.
How it works
There are exact formulas for simple cases, but the intuition matters more than the algebra. Risk of ruin rises when the win rate falls, when the edge shrinks, and — most of all — when the risk per trade goes up. The simple even-money version makes the last point clear:
Risk of ruin ≈ ((1 − edge) ÷ (1 + edge)) ^ (units of capital)
Here edge is your advantage per trade and units is how many equal bets your capital is divided into. Shrink the risk per trade and units climbs, and because it sits in the exponent, the ruin probability collapses. That single lever — bet size — does more than anything else in the equation.
A worked example
Two traders both have a genuine edge: they win 55% of even-money trades and lose 45%. Same positive expectancy. The only difference is bet size.
- Trader A risks 2% per trade. Capital is split into roughly 50 bets, and with a 55/45 edge the chance of ever being ruined is tiny — a fraction of 1%. A losing streak stings but cannot wipe them out.
- Trader B risks 25% per trade. The account is now only four bad trades from the floor. Even winning 55% of the time, four losses in a row will turn up, and reasonably soon — roughly a 1-in-20 stretch. Trader B's risk of ruin is high enough to be close to inevitable if they keep going.
Same edge, same win rate. The only change is bet size, and it is the difference between compounding for years and blowing up by Friday.
Why it matters
A positive edge only pays out if you are still trading when it arrives. Over-sizing is how traders with genuinely good systems still go to zero: the edge is real, but variance shows up before the edge does, and the account cannot absorb it. Risk of ruin is the bridge between "this strategy is profitable on average" and "this account is still alive next year" — and the second is the only one that pays.
Common misconceptions
- A winning system cannot blow up. It can, easily, if the risk per trade is high. An edge protects the average outcome, not the worst path to it.
- Ruin means zero. Usually it means the point where you stop — a prop-firm drawdown limit, or a psychological floor — which you reach long before zero.
- You cut it by tweaking entries. Mostly you cut it by cutting size. Small risk per trade — the 1% rule is the common anchor — does more than any entry change, and spreading capital across uncorrelated strategies helps further. Over-leveraging is the fastest way to push ruin toward certainty.
The Karnek note
Karnek cannot set your risk per trade, but it shows the two things that warn of ruin before it arrives — live drawdown, and how large each position is relative to the account. It reads read-only from the terminal, on your real trades, and can never place or size a trade itself.
Written and reviewed by the Karnek Research team. Last updated August 2026.
Educational content only - not financial advice. Past performance does not predict future results. Trading carries significant risk.