- Maths reviewed by Josh Miller
- Tested by Diana Westfield
This blackjack bankroll calculator works out your risk of ruin: the chance a counting bankroll goes to zero before the edge shows up. With a 1% edge, a £25 average bet and the swings of a 1-8 spread (about 2.8 bets per hand), you make around £20 an hour. A £10,000 bankroll carries a 36% risk of ruin. To get that to 5% you need about £29,400. It’s free, and it simulates sessions as well as doing the formula.
Blackjack bankroll and risk of ruin
The formula is the same one gamblers have used since the 1960s: e−2 × EV × bankroll ÷ variance, per hand. What makes blackjack interesting is the variance. Flat betting has a standard deviation of about 1.15 bets a hand. Spread from 1 to 8 units and it jumps to 2.5 to 3, because your big bets land in the shoes where you also double and split more.
That’s why the same edge needs a much bigger bank once you spread. The spread is where the edge comes from, and where the swings come from too.
What a winning counter’s hour looks like
£20 expected, ±£626 for one standard deviation. You’ll be behind after 100 hours more than a third of the time. To be fairly sure your results reflect skill and not luck, you need about N0 = (2.8 ÷ 0.01)² = 78,400 hands. At 80 hands an hour that’s nearly a thousand hours of play.
| Edge (SD 2.8, £25 average bet) | Win per hour | Bank for 5% risk | N0 (hands) |
|---|---|---|---|
| 0.5% | £10 | about £58,700 | 313,600 |
| 1.0% | £20 | about £29,400 | 78,400 |
| 1.5% | £30 | about £19,600 | 34,800 |
Basic strategy players
Set the edge to −0.5% and the SD to 1.15. The CasinoCalcs calculator says ruin is certain, and in the long run it is: with a negative edge, keep playing for ever and the bankroll goes. What it can’t tell you is how long it’ll last. For that, the blackjack simulator or the slot bankroll calculator logic is closer to the question you’re asking.
Lowering the risk
Three levers. Bet smaller: halve the average bet and the bank needed halves. Use a stop-loss and move down after a bad run, which the formula ignores. Or improve the game: better penetration and rules raise the edge, and edge helps more than anything. The card counting calculator shows how much a given true count is worth, and the blackjack house edge calculator prices the rules.
Blackjack session tracker
Counters live and die by their records. Log each session with your buy-in, cash-out and hours, plus your average bet and hands if you want the result as a share of money bet. A basic-strategy player should drift towards about −0.5% over time; a counter with a real edge should see it creep above zero, slowly.
Everything stays in this browser. Export a CSV now and then so a cleared history doesn’t take your record with it.
Counting doesn’t make losing runs smaller. It makes them survivable, with the right bank. BeGambleAware.org is free and confidential.