The single most common way card counters go broke isn’t getting caught — it’s betting too big for their bankroll and running into variance before their edge pays off. This calculator runs the math for your specific situation.
Blackjack Bankroll Calculator
Estimate your risk of ruin, Kelly-optimal bet size, and expected results as a card counter.
Your Situation
The Math Says
About these numbers
This calculator uses standard card-counting math. Variance is assumed at 1.32 per hand (standard deviation ≈ 1.15), which is the conventional figure for blackjack with Hi-Lo counting. Risk of ruin is approximated as e−2·(B/b)·(edge/variance) where B is your bankroll, b is your bet, and edge is your player advantage as a decimal.
Kelly-optimal bet is calculated as bankroll × (edge / variance). Full Kelly is mathematically maximum-growth but uncomfortably high variance in practice — most counters bet a fraction of Kelly. Half-Kelly is a common compromise.
Real-world results vary. The edge you actually realize depends on the rules of the game, your bet spread, penetration, counting accuracy, and playing deviations. A 1% edge is optimistic without a wide bet spread and good rules (S17, DAS, late surrender, 75%+ penetration).
What the numbers mean
Expected win per hour: On average, over a large number of hours, this is what you win. It’s not what you’ll win tonight. Single-session results are dominated by variance.
Hourly standard deviation: The scale of swings you should expect. If your expected hourly is $20 and your hourly SD is $280, it means a typical hour can land anywhere from losing $260 to winning $300 — roughly. That’s the range that will contain about two-thirds of your sessions.
Risk of ruin (RoR): The probability you lose your entire bankroll before you ever turn a sustained profit. This is the number that matters most. A 5% RoR means roughly one in 20 counters with your setup never makes it to profit.
Kelly-optimal bet: The bet size that maximizes long-term bankroll growth. Mathematically attractive, practically brutal — the variance of full Kelly betting is uncomfortable enough that most counters bet a fraction of it.
Half-Kelly: A common conservative choice that captures most of the growth rate with dramatically less variance.
Bankroll for target RoR: How much money you’d need, at this bet size, to achieve a given risk of ruin. If the calculator says you need $7,600 for 1% RoR and you have $3,000, that’s useful information.
How these numbers are computed
The calculator uses standard card-counting assumptions:
- Variance per hand: 1.32 (standard deviation ≈ 1.15 betting units). This is the conventional figure for blackjack with Hi-Lo counting.
- Risk of ruin formula: RoR ≈ exp(-2 · N · edge / variance), where N is bankroll-in-units. This is the exponential approximation widely used in counting literature.
- Kelly-optimal: bankroll × (edge / variance). Full Kelly for continuous outcomes.
What these numbers don’t capture
A few caveats worth understanding before you trust the output:
The edge you enter assumes accurate counting. If your counting accuracy is 90% (which is actually pretty good at casino speed), your realized edge is probably half of what a perfect counter would earn. Be realistic about your skill when you pick the edge input. For beginners, 0.3–0.5% is honest. For experienced counters with wide spreads and good rules, 0.8–1.2% is achievable. Above that is optimistic.
The bet size input is your weighted average. Counters don’t bet the same amount every hand — the whole point is to bet more at high counts and less at low counts. The “average bet” for the calculator is your weighted average across a session, not your maximum bet. If you bet $25 most of the time and $200 at the max, your weighted average is probably around $45, not $200.
Trip results aren’t session results. The session calculation assumes your bet size stays roughly constant. If you’re playing a real trip where your bankroll changes significantly, the dynamics are more complex — you’d ideally re-size your bets as bankroll grows or shrinks. The calculator gives you the static picture.
Ruin isn’t the only bad outcome. Even if you don’t go broke, you can have long, unpleasant downswings. A counter with a 1% edge and a 5% RoR will still have losing sessions, losing weeks, and occasionally losing months. That’s variance, not bad play. Bankroll discipline is what keeps you in the game long enough for the edge to matter.
Rough rules of thumb
- 200 units of bankroll at your average bet puts you at roughly 5% RoR with a 1% edge. This is a common benchmark.
- 300 units gets you to roughly 1% RoR with a 1% edge — a much safer number.
- If you’re playing a trip where you’ll only play a few hours, your trip bankroll needs to be at least 3× your hourly standard deviation — otherwise a normal bad session wipes you out.
- Half-Kelly bet sizing is almost always the right default. Full Kelly is theoretically optimal but emotionally exhausting.
For more context on why bankroll management matters, see our bankroll requirements article. For the counting skills the math assumes, start with our trainer.