The Probability of Blowing Up Your Trading Account

The Uncomfortable Truth

A strategy with a 55% win rate and 1:1.5 risk-reward has a positive expected value. The probability of account survival, however, depends critically on position sizing. According to a Barber, Lee, Liu & Odean study published in the *Review of Financial Studies* (2014), approximately 80% of active day traders lose money over a 12-month period — not because their strategies lack edge, but because of how they size positions.

Why Profitable Strategies Still Fail

The problem is variance. Short-term results are dominated by randomness, not edge. A coin flip with 55/45 odds will produce a losing streak of 7 or more trades approximately once every 100 trades (probability: ~1.5%). If you're risking 5% per trade, that streak creates a 30%+ drawdown before your edge has time to recover.

The Drawdown Trap

Most traders have a psychological ruin threshold that's much lower than 100% loss:

• At 20% drawdown: doubt creeps in
• At 30% drawdown: strategy changes start
• At 40% drawdown: most traders quit or revenge trade

A survey by the CFA Institute (2020) found that 62% of professional fund managers identified drawdown tolerance as the primary factor determining strategy longevity, ahead of absolute returns.

Your real ruin probability is the chance of hitting your psychological breaking point, not zero.

Understanding Your Real Risk

1. Know your win rate, average winner, and average loser

2. Define your personal ruin threshold (the drawdown that would make you stop)

3. Run simulations across thousands of randomized outcomes with those inputs

4. Look at the distribution, not the average

The Risk of Ruin Calculator gives you a quick estimate. RangeSight runs extended simulations with real volatility data for a complete picture.

Conceptually this provides a framework. In practice, outcomes vary across simulations. Testing multiple scenarios reveals how consistent a strategy actually is.