What risk percentage per trade keeps my risk of ruin below a target percentage?

How this is calculated

• This uses the same simplified "gambler's ruin" model as our Risk of Ruin Calculator, solved in reverse: instead of finding risk of ruin from a chosen risk per trade, this finds the risk per trade that produces your target risk of ruin.
• Edge equals (2 × your win rate) minus 1. Units of risk equal 100 divided by risk per trade. Risk of ruin equals ((1 − edge) ÷ (1 + edge)) raised to the power of units of risk.
• The model assumes a 1:1 risk-to-reward ratio, a fixed percentage risked every trade, independent trade outcomes, and an indefinitely long series of trades. A favorable risk/reward ratio, where your average winner beats your average loser, lowers your true risk of ruin below what this simplified model shows.
• If your win rate is 50% or below, this model shows 100% risk of ruin no matter how small your risk per trade is. Position sizing alone cannot fix a system with no edge under this 1:1 assumption.
• Treat the result as a theoretical ceiling, not a recommendation. Trading anywhere close to this maximum means accepting far more balance swings than most traders find comfortable in practice.