Risk of Ruin

Expectancy says a strategy makes money in the long run. Risk of ruin asks the question that comes first: do you survive the short run to get there? It is the number most retail traders never compute, and the one that explains most blown accounts that had a real edge.

What ruin means here

Ruin does not mean a zero balance. It means falling to a level from which you stop — because the account is too small to trade the plan, because the broker minimum is now larger than your correct size, or because you have had enough.

The site's calculator lets you set that level, and reports two related numbers:

• Risk of ruin — the chance of ever falling that far below your starting balance during the run.
• Risk of drawdown — the chance of ever falling that far below your running peak. This is always the larger of the two, because a peak you reached along the way gives the decline further to travel.

Both are probabilities over a finite run of trades, which is what makes them useful. "Eventually" is not a horizon anyone trades; the next 200 trades is.

Inputs that drive it

Four inputs, all of which you already have from the previous lessons.

The order matters. Traders spend most of their effort on the first two — better entries, better win rate — and the fourth column says the third input outweighs both. You cannot out-edge bad sizing.

Why 1 percent and 3 percent are not three times apart

Here is a strategy with a genuine edge: 40% win rate at 2:1 reward-to-risk, which is +0.20R per trade. Ruin is defined as a 50% fall, over 200 trades.

Tripling the risk from 1% to 3% did not triple the danger. It moved it from effectively zero to about one account in seventy, and the drawdown column from zero to one in thirteen. From 1% to 5% — five times the risk — ruin goes up by a factor of hundreds, and a 50% drawdown becomes a coin flip.

The mechanism is that losses compound. Two 5% losses do not cost 10%; they cost 9.75% of a balance that is now generating smaller wins. Past a threshold the arithmetic of recovery from the previous lesson turns against you faster than the edge can repair it.

And with a weaker edge

The same experiment at 50% win rate and 1.2:1 — still positive, at +0.10R — is worse at every level: 1.8% ruin at 3%, and 12.7% at 5% risk. With no edge at all (50% at 1:1), risking 5% gives a 43% chance of ruin over the same 200 trades, which is what a coin flip traded aggressively does to an account.

Picking a number you can live with

Now the rule of thumb from lesson 1 can be replaced with a decision. Work backwards from the risk of ruin you are willing to accept.

• Decide the acceptable probability. Under 1% over your next 200 trades is a defensible standard. Zero is not available.
• Use your real statistics, from at least 100 trades. Optimistic inputs produce an optimistic answer, and this is the one calculation where flattering yourself is expensive.
• Read the largest risk percent that stays under your threshold, then trade less than it. The model assumes your edge holds and your execution is perfect; neither is true.

For most retail plans this lands between 0.5% and 2%, which is where the conventional advice sits — but now you know why, and you can tell whether your own numbers put you at the top or the bottom of that range.

One consolation. Everything in this lesson says the same thing as everything in the last four, which is a sign the subject is simpler than it looks: size small enough that no realistic streak takes you out, and the edge gets time to work. The rest of this track is that sentence applied to particular situations.