Risk of Ruin
The math behind bankroll survival
What Is Risk of Ruin?
Even with a positive edge, card counting is a long-term game. In the short term, variance dominates — you will go through losing streaks that can feel endless. Risk of Ruin (RoR) is the probability that you lose your entire bankroll before your edge has time to compound.
Key Terms
Bankroll — the total amount of money you have set aside exclusively for playing blackjack. This is not your savings or living expenses; it is money you can afford to risk. The size of your bankroll relative to your minimum bet is the most important factor in whether you survive long enough to realize your edge. A common guideline is 200–500 minimum bets.
Edge — your expected profit per dollar wagered, expressed as a percentage. A +1% edge means you expect to win $1 for every $100 bet on average. Your edge comes from bet variation (betting more at high counts) and play deviations.
Variance — a measure of how much individual hand outcomes swing around the expected value. Blackjack has high variance because of doubles, splits, and blackjack payouts. High variance means bigger swings and longer losing streaks, even with a positive edge.
E[bet] — the average bet size under your spread, accounting for how often each true count occurs. With a bet spread, you bet more at high counts and less at low counts, so your average bet is larger than the minimum.
The Formula
Where B is your bankroll measured in minimum bets, V is variance per unit bet (computed from simulation), and E[bet²] is the expected squared bet under the spread (which captures how volatile the bet sizes themselves are). Most counters target a RoR below 5%.
Risk of Ruin
Probability of losing your entire bankroll at different bankroll sizes (in min bets)