Risk of Ruin
Trading Intelligence
9 min read
riskOfRuin
Compute the probability of account wipeout given your win rate, payoff ratio, and risk per trade to ensure long-term survival.
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9 min read
Compute the probability of account wipeout given your win rate, payoff ratio, and risk per trade to ensure long-term survival.
Every edge can fail if you risk too much. This is the math that tells you how likely it is to survive long enough to win.
You’ve got a system. You’ve got a positive edge. You’ve got your journal full of +0.5R and +2R wins.
But there’s a lurking question every pro eventually faces:
❓ “How likely am I to lose so much in a row that I can’t recover?”
That’s what Risk of Ruin (RoR) answers — mathematically.
And if you’re trading without knowing it?
You may be optimizing toward performance — but gambling with survival.
Let’s fix that.
Risk of Ruin is the probability that your account hits a critical loss level (e.g. 50%, 80%, 100%) before recovery.
In other words:
This isn't fear-mongering — it’s pure math.
Even with a solid edge, risking too much can guarantee failure over time.
For fixed fractional risk and symmetrical outcomes:
RoR ≈ [(1 – Edge) / (1 + Edge)] ^ (Capital / Risk per trade)
Where:
Let’s break it down with an example.
Now estimate:
RoR ≈ [(1 – 0.35) / (1 + 0.35)] ^ (100 / 2)
RoR ≈ (0.65 / 1.35)^50
RoR ≈ (0.481)^50 ≈ 0.00000008 → effectively **0%**
With a good edge and conservative risk, your chance of ruin is nearly zero.
Try 10% risk per trade instead of 2%:
(0.481)^(100 / 10) = (0.481)^10 ≈ 0.0025 → RoR = **0.25%**
Now imagine 30% risk per trade: → RoR skyrockets → You’re essentially guaranteed to blow up within a small sample.
Edge doesn’t matter if your size is too big.
Monte Carlo simulates thousands of trade sequences using your stats, generating:
Useful for:
We can build this in later posts/tools if you’d like.
| Principle | Recommendation |
|---|---|
| Use fixed % risk per trade | 0.5%–1.5% for most systems |
| Know your EV and variance | From backtest or real journaled data |
| Simulate worst streaks | Use rolling drawdowns or MC simulation |
| Accept a soft stop threshold | Pause at 15–20% drawdown, reduce size |
| Re-validate after 100+ trades | Edge may decay, RoR must adapt |
Risk of Ruin is the math behind why traders who “almost made it” disappear.
Don’t assume your edge will save you — design your risk so it survives long enough to matter.
Let others blow up trying to make 5% a day. You’ll still be here in 5 years — compounding confidently.