Free tool

Bankroll and swings

A good play can still lose, and so can the next few. Your bankroll has to last through those losing runs for the edge to pay off. Enter what a typical play is worth and how much it swings, and see how likely your bankroll is to make it.

Your plays

Example numbers
What one play is worth on average (its expected value). The expected profit from the must-hit-by calculator is this number.
One standard deviation of a play's result: how far a typical play lands from the average. Jackpot plays swing a lot.
Money set aside for plays, apart from money you need.
How many plays like this you expect to make, say over the next few months (1 to 5,000).

The numbers filled in are an example, not a real machine. Put in your own.

Risk of ruin--

Chance of going broke

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Bankroll for 5% risk
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Bankroll for 1% risk
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Behind after 50 plays
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For a 90% chance to be ahead
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A bad stretch over 50 plays (1 in 10)
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Risk of ruin = e−2 × average × bankroll ÷ swing². It treats each play's result as bell-shaped. Real slot plays are lumpier, so read these as a guide, not a promise.

Chance of going broke at each bankroll

Show the numbers
Bankroll it takes at each level of risk
Risk of going brokeBankroll it takes

How to read it

  • Chance of going broke is the share of players starting with this bankroll who would lose all of it before their edge paid off, if they kept making plays just like this one with no end date. Under 5% is comfortable. Over 20% means an ordinary losing run will probably wipe you out.
  • Behind after a number of plays is how often a player with a real edge is still down after that many plays. Being down early is common even when every play is a good one, so it is not proof the edge is gone.
  • A bad stretch is the drop from a high point to a low point that one player in ten will hit within those plays. Make sure you can sit through it without quitting or reaching for money you need.

Risk falls fast as the bankroll grows: doubling the bankroll squares the risk, so 10% becomes 1%. Halving it does the reverse. If the number is too high, play smaller bets on the same kind of plays. That shrinks the average and the swing together, which has the same effect as a bigger bankroll.