Bankroll Calculator
A $2,000 bankroll betting $25 units (80 units) has a ~29.8% chance of ever going broke at this edge and variance — most pros aim for under 5%.
Educational math, not betting advice. Risk of ruin here is the long-run kind — the chance of ever losing the whole bankroll playing this game indefinitely — and N0 is how many hands it takes for the edge to overcome one standard deviation of luck. Everything on this site runs on play money.
The risk-of-ruin math, shown honestly
This blackjack bankroll calculator runs the standard risk-of-ruin formula from the card counting literature: RoR = ((1 − e/s) ÷ (1 + e/s))^(B/s), where e is your edge per hand, s is the standard deviation per hand in units, and B is your bankroll in units. It models unlimited play with no stop point, which is the honest version — a long losing streak doesn't care about your schedule. The same three inputs also give N0, the number of hands (s/e)² it takes for the edge to overcome one standard deviation of luck, and your expected hourly win: edge × average bet × hands per hour.
The defaults are sourced, not invented. A good counter's overall edge is realistically 0.5–1.5% — the house edge math explains where the baseline comes from. Flat-betting one hand carries a standard deviation near 1.15 units, but nobody counts cards to flat-bet: the bet spread that turns the count into money also inflates variance well past 2 units per hand, which is exactly why the bankroll requirement balloons from ~200 units to the 300–1,000 units serious counters actually carry. Hands per hour runs from about 52 at a full table to 209 heads-up, and it multiplies both your expected win and how fast the variance arrives.
Honest caveats: the formula is an approximation (a good one when the edge is small relative to the variance, which it always is in blackjack), it slightly overstates true risk, and the real numbers shift with rule variations, penetration and your spread — serious study ends at simulation software, not a napkin formula. Nothing here is betting advice; it's the applied probability behind why counting is a grind even when it works. If you want the skill and not just the math, the card counting trainer drills the count itself — with play money and zero risk of ruin.
Bankroll & risk of ruin FAQ
What is risk of ruin in blackjack?
Risk of ruin is the probability that ordinary losing streaks wipe out your entire bankroll before your edge has time to show up. Even a player with a genuine 1% advantage loses constantly hand to hand — the edge only surfaces across thousands of hands, and a bankroll that is too small for the bet size can easily go broke first. The classic formula computes that probability from three numbers: edge per hand, standard deviation per hand, and bankroll measured in betting units.
How big should a card counting bankroll be?
It depends on the risk you accept. With a ~1% edge and flat-bet variance, roughly 200 units holds long-run risk of ruin near 5%. But counters don't flat-bet — spreading bets raises the standard deviation per hand to 2 or 3 units, and at that variance the same 5% target needs on the order of 1,000 units. That is why the counting literature talks about 300–1,000 unit bankrolls, and why a popular rule of thumb calls for about 100 times your maximum bet.
What unit size should I use?
Work backwards from the bankroll rather than forwards from the bet you'd like to make: divide your bankroll by the number of units your target risk of ruin requires. A $10,000 bankroll that needs 500 units implies $20 units — not the $100 units that feel proportionate. If the resulting unit is below the table minimum you can find, the honest conclusion is that the bankroll is too small for that game, not that the math is too conservative.
Does this calculator apply if I don't count cards?
Yes, but the answer it gives is blunt: with zero or negative edge, long-run risk of ruin is 100% — every bankroll goes broke eventually, and no bankroll size or betting system changes that. That's not a flaw in the formula, it's the formula working. Basic strategy without counting faces roughly a 0.5% house edge, so the same math that sizes a counter's bankroll is the math that guarantees the house wins in the long run.